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1
Schmitte, Till. "Bragg-MOKE and Vector-MOKE investigations magnetic reversal of patterned microstripes /." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=967231663.
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Ouahioune, Nedjma. "MOKE set-upto measure magnetic anisotropy : MOKE set-upto measure magnetic anisotropy." Thesis, Uppsala universitet, Materialfysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-414388.
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Jordan, Simon Mark. "The MOKE characterisation of magnetic multilayers." Thesis, University of York, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284135.
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Westphalen, Andreas. "Advanced MOKE investigations remagnetisation processes of microsized structures." Berlin dissertation.de, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=2935096&prov=M&dok_var=1&dok_ext=htm.
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Persson, Måns, and Filip Lindh. "Optimisation of measuring magneticproperties of micro-structuresusing the magneto-optic Kerr effect." Thesis, Uppsala universitet, Materialfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-306118.
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Magnetic storage means storage of data using magnetised medium and is widespreadover the world today, especially in hard disk drives. Using this kind of storagerequires knowledge about these materials. A way to study thin magnetic materials isto use MOKE(magneto optical Kerr effect). A Moke-system is a setup to measure thinmagnetic films by shooting a laser and analyze the reflected beam.The purpose of this report is to document and if possible improve a MOKE-system,named HOMER. This includes temperature regulation, filters, amplifiers, opticalchopper, Helmholtz coils and a laser. HOMER was documented and some changeswere made. The PID-parameters were set successfully. A low pass filter wasremoved, which decreased the noise. Using an optical chopper and lock in amplifierhowever did not decrease the noise. A labview program was written to demagnetizethe samples in a certain time which seemed to work properly. The hall probe in thesystem was successfully calibrated.
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Dufour, Pauline. "Moke microscope measurements ofmagnetic domains in micro-structuresof Fe80Zr10B10." Thesis, Uppsala universitet, Materialfysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-355746.
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Gester, Matthias. "Structural and magnetic properties of epitaxial Fe and Co films on GaAs substrates." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338052.
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Yu, Wei. "Time resolved Kerr microscopy of materials and devices for magnetic data storage applications." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/15365.
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Time resolved scanning Kerr microscopy (TRSKM) has been used to study a number of different magnetic systems. Firstly, partially built hard disk writer structures, with a multilayered yoke formed from 4 repeats of a NiFe(~1 nm)/CoFe(50 nm) bilayer, and with three coil windings underneath, were studied by TRSKM with unipolar driving pulses. Dynamic images of the in-plane magnetization suggest an underlying closure domain equilibrium state. This state is found to be modified by application of a bias magnetic field and also during pulse cycling, leading to different magnetization rotation and relaxation behaviour within the tip region. Studies of a further three yokes with the same stack structure, but with only one coil winding at different positions beneath the yoke, yielded dynamic images of “flux beaming” in a channel parallel to the driving field. The magnetic contrast was strongest when the active coil was located near the centre of the yoke, while relaxation after removal of the excitation was most complete when the active coil was located near the confluence region. These results confirm the need for a multi-turn coil to ensure effective flux propagation along the entire length of the yoke. Furthermore, a structure with a NiFe/CoFe/Ru/NiFe/CoFe synthetic antiferromagnetic (SAF) yoke was studied as a bipolar current pulse with 1MHz repetition rate was delivered to the coil. The component of magnetization parallel to the symmetry axis of the yoke was compared at the pole and above a coil winding in the centre of the yoke. The two responses are in phase as the pulse rises, but the pole piece lags the yoke as the pulse falls. The Kerr signal is smaller within the yoke than within the confluence region during pulse cycling. This suggests funneling of flux into the confluence region. Dynamic images acquired at different time delays showed that the relaxation is faster in the centre of the yoke than in the confluence region, perhaps due to the different magnetic anisotropy in these regions. Although the SAF yoke is designed to support a single domain to aid flux conduction, no obvious flux beaming was observed, suggesting the presence of a more complicated domain structure. The SAF yoke writer hence provides relatively poor flux conduction but good control of rise time compared to single layer and multi-layered yokes studied previously. Secondly, vortex dynamics within arrays of square ferromagnetic nano-elements have been studied using TRSKM with coherent microwave excitation. It is shown that TRSKM can be used to detect vortex gyration in square nanomagnets with a lateral size (250nm) that is smaller than the diameter (300nm) of the focused laser beam. In an array with large element separation and negligible dipolar interaction, TRSKM images acquired at a fixed point in the microwave cycle reveal differences in the phase of the dynamic response of individual nanomagnets. While some variation in phase can be attributed to dispersion in the size and shape of elements, the circulation and polarization of the vortex are also shown to influence the phase. In an array with element separation smaller than the optical spot size, strong magneto optical response was observed within small clusters of elements. Micromagnetic simulations performed for 2 x 2 arrays of elements show that a certain combination of circulation and polarization values is required to generate the observed magneto-optical contrast. Thirdly, polar TRSKM has been used to directly observe magnetostatically coupled transverse domain walls (TDWs) in a pair of closely spaced, curved nanowires (NWs). Kerr images of the precessional response revealed a minimum in the Kerr signal due to the TDW in the region of closest NW separation. When the TDWs were ejected from the NW pair, the minimum in the Kerr signal was no longer observed. By imaging this transition, the static decoupling field was estimated to lie between 38 and 48 Oe, in good agreement with a simple micromagnetic model. This work provides a novel technique by which DC and microwave assisted decoupling fields of TDWs may be explored in NW pairs of different width, separation, and curvature. Fourth, time resolved magneto-optical Kerr effect and phase modulated X-ray ferromagnetic resonance measurements have been performed on a CoO/Py bilayer for different temperatures, RF frequency, and CoO thickness. Kerr hysteresis loops did not show any evidence of exchange bias for temperatures between 200K and 330K for any thickness of CoO, but the coercivity was found to increase with increasing CoO thickness and decreasing temperature. Magneto-optical FMR and XFMR data showed some asymmetry with respect to the sign of the bias field, but the amplitude of the signals decreased rapidly with decreasing temperature. The results are consistent with the appearance of frustrated antiferromagnetic order within the CoO during field cooling.
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Seu, Keoki A. "Static and ultrafast MOKE studies of exchange -biased cobalt systems." W&M ScholarWorks, 2006. https://scholarworks.wm.edu/etd/1539623503.
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We have studied the exchange bias interaction in metal bilayers IrMn/Co and FeMn/Co using the static and ultrafast pump-probe Kerr effects. Experiments conducted on wedged Co samples show that the exchange bias interaction is sensitive to the buffer layers grown beneath it when the antiferromagnetic layer is FeMn. The exchange bias strength, as measured by the shift in the magnetic hysteresis loop, follows a 1/tFM dependence as reported in the literature. The time-domain pump-probe experiments reveal coherent magnetization oscillations, whose frequencies are comparable to those measured by frequency-domain FMR measurements, and they fit well to FMR equations for the frequency. We have also been able to use the pump beam to permanently alter the exchange bias interface which leads to the launching of oscillations along new geometries, particularly along the easy axis where magnetization is aligned with the applied field. This is explained qualitatively by showing that the pump has enough energy to overcome the energy barrier in the AF, allowing it to flip and provide a torque on the magnetization that launches oscillations.
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Зленко, Віталій Олександрович, Виталий Александрович Зленко, Vitalii Oleksandrovych Zlenko, Максим Геннадійович Демиденко, Максим Геннадьевич Демиденко, Maksym Hennadiiovych Demydenko, Сергій Іванович Проценко, Сергей Иванович Проценко, and Serhii Ivanovych Protsenko. "Synthesis and magneto-optical properties of Co nanoparticle arrays." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35380.
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In this paper described a technique for obtaining arrays of magnetic nanoparticles on amorphous Si3N4
substrates during annealing of thin Co films. Magneto-optical properties of the nanoparticle arrays were
studied using MOKE. It was shown the dependence of magneto-optical properties of nanoparticle arrays
from their morphology.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35380
11
Stångberg, Valgeborg Fredrik. "Element-Specific Magnetization Dynamics Using T-MOKE at the HELIOS Laboratory." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-297598.
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Magnetism is a familiar phenomenon, and is applied in a variety of devices, from simple ones, like compasses, to the more sophisticated magnetic hard disk drives. It is also known that the magnetization of a material can change, for example by heating or by exposure to an external magnetic field. The dynamics of transitions between different magnetizations, however, is largely unknown, particularly in complex materials. To further the understanding of such dynamics, this thesis presents an observational study of the dynamics of laser induced demagnetization of permalloy (Ni0.8Fe0.2). Dynamics were studied with element-specificity, i.e. Fe and Ni were studied simultaneously, but separately, rather than studying the overall material. The study was conducted at the HELIOS laboratory at Uppsala University, which features equipment for the study of magnetization dynamics. Important concepts like high-order harmonic generation (HHG) and the transverse magneto-optic Kerr effect (T-MOKE) are discussed. HHG is the laser induced generation of high energy photons, and T-MOKE relates the intensity of reflected light to the magnetization of the reflecting material. The study revealed a very short demagnetization time, and maximum demagnetization of both elements was achieved within 1 picosecond. An onset delay in the demagnetizations of Fe and Ni of about 25 femtoseconds was also observed. Both phenomena have been previously reported. The results further imply that the magnetizations diverge over a 10 picosecond time interval after the onset of demagnetization, which has not been previously reported. The apparent divergence may be due to an unknown transient setup-related issue. The short demagnetization times, as well as the onset delay could potentially contribute to the development of a more complete theory of magnetization dynamics.Magnetism är ett bekant fenomen, som utnyttjas i allt från enkla tillämpningar, som kompasser,till mer sofistikerade sådana, som hårddiskar. Det är också känt att magnetiseringen i ett material kan ändras, t.ex. genom upphettning eller genom att det utsätts för ett yttremagnetiskt fält. Dynamiken vid övergångar mellan olika magnetiseringstillstånd är dock ett relativt okänt ämne, i synnerhet när det kommer till komplexa material. För främjandet av en större förståelse inom ämnet, presenteras här en observationell studie av dynamiken för laserinducerad avmagnetisering av permalloy (Ni0.8Fe0.2). Dynamiken undersöktes med grundämnesspecificitet, d.v.s. Fe och Ni undersöktes samtidigt, men var för sig, snarare än att materialet undersöktes som helhet. Undersökningen gjordes vid HELIOS-laboratoriet vid Uppsala Universitet, som tillhandahåller utrustning för undersökning av magnetiseringsdynamik. Viktiga koncept diskuteras, såsom övertonsgenerering och den transversella magnetooptiska Kerr-effekten (T-MOKE). Övertonsgenerering innebär laserinducerad generering av högenergifotoner, och T-MOKE relaterar reflekterad intensitet till magnetiseringen i det reflekterande materialet. Undersökningen påvisade en mycket kort avmagnetiseringstid, och maximal avmagnetisering nåddes inom en pikosekund. En relativ tidsförskjutning mellan avmagnetiseringsförloppen för Fe och Ni om ungefär 25 femtosekunder observerades också. Båda fenomen har rapporterats tidigare. Resultatet visar även en divergens mellan magnetiseringsförloppen under ett tidsspann på 10 pikosekunder efter avmagnetiseringens början, vilket inte har rapporterats förr. Den skenbara divergensen kan bero på ett okänt, tillfälligt problem i uppställningen. Den korta avmagnetiseringstiden och den relativa tidsförskjutningen skulle kunna bidra till utvecklingen av en mer komplett teori för magnetiseringsdynamik.
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Fugattini, Silvio. "Studio mediante magnetometro moke di film sottili di manganite per applicazioni in spintronica." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8334/.
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In questo lavoro di tesi è stata studiata l'anisotropia magnetica di film sottili epitassiali di La0.7Sr0.3MnO3 (LSMO), cresciuti con la tecnica Channel Spark Ablation su substrati monocristallini di SrTiO3 (001).
L'interesse nei confronti di questi materiali nasce dal fatto che, grazie alla loro proprietà di half-metallicity, sono usati come iniettori di spin in dispositivi per applicazioni in spintronica, l'elettronica che considera elemento attivo per l'informazione non solo la carica elettrica ma anche lo spin dei portatori. Un tipico esempio di dispositivo spintronico è la valvola di spin (un dispositivo costituito da due film ferromagnetici metallici separati da uno strato conduttore o isolante) il cui stato resistivo dipende dall'orientazione relativa dei vettori magnetizzazione (parallela o antiparallela) degli strati ferromagnetici. E’ quindi di fondamentale importanza conoscere i meccanismi di magnetizzazione dei film che fungono da iniettori di spin.
Questa indagine è stata effettuata misurando cicli di isteresi magnetica grazie ad un magnetometro MOKE (magneto-optical Kerr effect). Le misure di campo coercitivo e della magnetizzazione di rimanenza al variare dell'orientazione del campo rispetto al campione, permettono di identificare l'anisotropia, cioè gli assi di facile e difficile magnetizzazione.
I risultati delle misure indicano una diversa anisotropia in funzione dello spessore del film: anisotropia biassiale (cioè con due assi facili di magnetizzazione) per film spessi 40 nm e uniassiale (un asse facile) per film spessi 20 nm. L'anisotropia biassiale viene associata allo strain che il substrato cristallino induce nel piano del film, mentre l'origine dell'uniassialità trova la giustificazione più probabile nella morfologia del substrato, in particolare nella presenza di terrazzamenti che potrebbero indurre una step-induced anisotropy. Il contributo di questi fattori di anisotropia alla magnetizzazione è stato studiato anche in temperatura.
13
Dias, André. "Development of a scanning MOKE system with a 10 T pulsed magnetic field source." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY099.
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Nous avons développé un système de mesure magnéto-optique à balayage basé sur l’Effet Kerr(MOKE). Le montage permet mesurer des cycles d'aimantation en balayant de larges surfaces (150 x 150 mm 2 ) sous un champ magnétique pulsé allant jusqu’à 10 T à température ambiante. Les champs magnétiques intenses sont produits par des bobines millimétriques (diamètre interne = 3 mm) connectées à un générateur de courant bipolaire pulsé. Nous avons pu démontrer que ce système présente un fort potentiel pour l'étude combinatoire de couches magnétiques dures. Pour cela, nous avons dressé grâce à notre système MOKE la carte 2D des courbes d’hystérèse pour des couches de SmCo et NdFeB élaborées par pulvérisation et présentant un gradient de composition et comparé avec des mesures de composition d'alliage (EDX) et l'analyse de la structure cristalline (XRD)The aim of this PhD project is to study diamagnetic levitation at the micro-scale in a quantitative fashion and to explore its use for the precise positioning and controlled movement of micro/nano-objects. Diamagnetic materials will be prepared with controlled shape and size (µm-mm range). Micro-magnets will also be developed to levitate the diamagnetic objects or to levitate above diamagnetic surfaces. To complement the study, a fully automated scanning MOKE system will be developed in order to characterize the quality of our samples fabricated using the triode sputtering machine and applying techniques called micro magnetic transfer and micro flux concentrators. First simple micro-robotic devices will be designed, and hopefully tested
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Patton, Heather M. A. "THE FABRICATION OF HEUSLER ALLOY THIN FILMS FROM MULTIPHASE TARGETS USING PULSED LASER DEPOSITION." Available to subscribers only, 2009. http://proquest.umi.com/pqdweb?did=1796120911&sid=4&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Baudot, Grégory. "Nano-structures magnétiques auto-organisées : le cas du cobalt sur les surfaces vicinales de l'or (111)." Paris 7, 2003. https://tel.archives-ouvertes.fr/tel-00004422.
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Bsatee, Mohammed N. "The Development of Experimental Setup for Various Magneto-Optical Studies." Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1438868631.
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Tanaka, Hiroki. "Development of MOKE Spectrometer for Magneto-optical Studies of Novel Magnetic Materials and Quantum Structures." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1226965026.
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Tan, Xiaojing. "Study of magnetic thin films and magnetic interfaces by linear MOKE and second harmonic generation." Diss., UC access only, 2009. http://proquest.umi.com/pqdweb?index=146&did=1907174011&SrchMode=1&sid=1&Fmt=7&retrieveGroup=0&VType=PQD&VInst=PROD&RQT=309&VName=PQD&TS=1270495163&clientId=48051.
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Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Includes bibliographical references (leaves 145-148). Issued in print and online. Available via ProQuest Digital Dissertations.
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Sheffield, Matthew E. "Developing New Techniques for Investigating Static and Dynamic Magnetic Degrees of Freedom." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu153304892098996.
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Benini, Mattia. "Investigations of ferromagnet-organic bilayers for application in spintronics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15788/.
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La spintronica è una branca dell’elettronica che sfrutta oltre alla carica, lo spin dell’elettrone per il trasporto dell'informazione. Il dispositivo spintronico modello, chiamato spin valve, è costituito da strati ferromagnetici disaccoppiati tra loro attraverso un materiale non magnetico di diversa natura. Più recentemente il campo della spintronica si è orientato verso l’uso di semiconduttori organici come materiali non magnetici dando origine alla cosiddetta “organic spintronics”. Dopo i primi successi di integrazione di materiali organici in dispositivi spintronici, sono emerse alcune peculiarità dei comportamenti magnetoresistivi che indicano come le molecole giochino un ruolo maggiore rispetto al mero trasporto di correnti spin-polarizzate. A questo concetto è stato associato al termine spinterface. Questo nuovo tipo di interfacce è di notevole interesse in molteplici campi oltre la spintronica, come l’optoelettronica o le memorie magnetiche.
In questo lavoro di tesi si sono studiate proprietà magnetiche di bistrati cobalto/fullerene e cobalto/gallio-quinolina, con l’obiettivo di verificare il ruolo del materiale organico nella definizione delle proprietà magnetiche dello strato di cobalto, con l’obiettivo di verificare la presenza di effetti di “spinterface”.
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Watarai, H. "Magneto-Optical Characterization of Binding Ability of Magnetic Nanoparticles in Solution." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42805.
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The magnetization profile of iron oxide magnetic nanoparticles (MNPs) and the binding ability of MNPs with metal ions in aqueous solutions were investigated by means of the magnetic linear dichroism (MLD) and the magneto-optical Kerr effect (MOKE) measurements. The ultra-visible MLD spectra of the non-modified and surface modified MNPs with -COOH showed a typical magnetization curve for a superparamagnetic
particles. Also, the MLD spectra were changed drastically by the addition of dysprosium(III) ion and showed that MLD spectra can be used for the evaluation of metal-MNPs binding ability. Furthermore, the magnetization of MNPs solution was measured sensitively by the transversal MOKE measurements, where a polarized beam was reflected at the interface of prism/solution of MNPs.
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Neal, Jeremy R. "The Magnetic Properties of Permalloy Antidot Arrays." Miami University / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=miami1060098522.
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Чешко, Ірина Володимирівна, Ирина Владимировна Чешко, Iryna Volodymyrivna Cheshko, Ірина Михайлівна Пазуха, Ирина Михайловна Пазуха, Iryna Mykhailivna Pazukha, Сергій Іванович Проценко, et al. "Magnetoresistive and Magnetooptical Properties Nanosize Film Systems Based on Fe and Au." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35237.
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The results of research magnetoresistive and magnetooptical properties of nanosize film systems based
on Fe and Au are presented. It was shown that the value of magnetoresistance and magnetooptical properties
depends on phase state of systems, concentration of Fe atoms and annealing temperature.
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Froemel, Paul. "Implementation of a T-MOKE setup for transient studies of magnetic materials at the HELIOS XUV photon sourc." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-224443.
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Pärnaste, Martin. "The Influence of Interlayer Exchange Coupling on Magnetic Ordering in Fe-based Heterostructures." Doctoral thesis, Uppsala universitet, Fysik III, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7885.
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Temperature dependent magnetization measurements were conducted on Fe-based heterostructures. A linear increase of the magnetic critical temperature with increasing Fe thickness was found for Fe/V superlattices with strong interlayer exchange coupling. For weakly coupled Fe/V superlattices anomalous values of the critical exponent β were attributed to differences in the effective interlayer exchange coupling in the surface region and in the interior of the superlattice stack. Hydrogen loading of a sample containing a thin Fe film, up to a maximum pressure of 4 mbar gave an increase of the magnetic critical temperature of ≈21 K. A sample with a double layer of Fe, exchange coupled over V, showed oscillations in the critical temperature when loaded to increasing pressure of hydrogen. The oscillations in the critical temperature indicate the presence of quasi-2D phases. Superlattices of Fe and V were investigated by x-ray magnetic circular dichroism. It was found that the orbital magnetic moment shows the same trend as the magnetic anisotropy energy with thickness of the Fe layers. A model which takes into account a varying strain and interface density successfully described the changes in the orbital magnetic moment. The magnetization was measured as a function of temperature for a series of magnetically δ-doped Pd samples. A thin film of Fe induced a magnetic moment in surrounding Pd layers, leading to a magnetic thickness one order of magnitude larger than the thickness of the Fe film. A crossover in the magnetic spatial dimensionality was found as the thickness of the Fe film increased from ≈0.4 monolayers to ≈1 monolayer. First principle calculations of the magnetization profile together with a spin wave quantum well model were used to explain the dimensionality crossover by an increase in the available thermal energy for population of perpendicular spin wave modes.
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Souza, Thatyara Freire de. "Multicamadas Ferromagn?ticas Nanom?tricas Peri?dicas e Quasiperi?dicas." Universidade Federal do Rio Grande do Norte, 2010. http://repositorio.ufrn.br:8080/jspui/handle/123456789/16569.
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Previous issue date: 2010-10-21Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
We present a study of nanostructured magnetic multilayer systems in order to syn- thesize and analyze the properties of periodic and quasiperiodic structures. This work evolved from the deployment and improvement of the sputtering technique in our labora- tories, through development of a methodology to synthesize single crystal ultrathin Fe (100) films, to the final goal of growing periodic and quasiperiodic Fe/Cr multilayers and investi- gating bilinear and biquadratic exchange coupling between ferromagnetic layer dependence for each generation. Initially we systematically studied the related effects between deposition parameters and the magnetic properties of ultrathin Fe films, grown by DC magnetron sput- tering on MgO(100) substrates. We modified deposition temperature and film thickness, in order to improve production and reproduction of nanostructured monocrystalline Fe films. For this set of samples we measured MOKE, FMR, AFM and XPS, with the aim of investi- gating their magnocrystalline and structural properties. From the magnetic viewpoint, the MOKE and FMR results showed an increase in magnetocrystalline anisotropy due to in- creased temperature. AFM measurements provided information about thickness and surface roughness, whereas XPS results were used to analyze film purity. The best set of parame- ters was used in the next stage: investigation of the structural effect on magnetic multilayer properties. In this stage multilayers composed of interspersed Fe and Cr films are deposited, following the Fibonacci periodic and quasiperiodic growth sequence on MgO (100) substrates. The behavior of MOKE and FMR curves exhibit bilinear and biquadratic exchange coupling between the ferromagnetic layers. By computationally adjusting magnetization curves, it was possible to determine the nature and intensity of the interaction between adjacent Fe layers. After finding the global minimum of magnetic energy, we used the equilibrium an- gles to obtain magnetization and magnetoresistance curves. The results observed over the course of this study demonstrate the efficiency and versatility of the sputtering technique in the synthesis of ultrathin films and high-quality multilayers. This allows the deposition of magnetic nanostructures with well-defined magnetization and magnetoresistance parameters and possible technological applications
Nesta tese apresentamos um estudo desenvolvido em sistemas magn?ticos de multica-madas nanoestruturadas, com o objetivo principal voltado a s?ntese e an?lise das propriedades de estruturas peri?dicas e quasiperi?dicas. Este trabalho evolui desde a implanta??o e o dom?nio da t?cnica de sputtering em nossos laborat?rios, passando pelo desenvolvimento de uma metodologia para a s?ntese de filmes nanom?tricos monocristalinos de Fe (100), at? o objetivo final de crescer multicamadas do tipo Fe/Cr peri?dicas e quasiperi?dicas e analisar o comportamento do acoplamento entre as camadas ferromagn?ticas de acordo com a gera??o da amostra. Primeiramente estudamos de maneira sistematica os efeitos relacionados entre os par?metros de deposi??o e as propriedades magn?ticas de filmes nanom?tricos de Fe, crescidos por DC sputtering em substrato de MgO (100). Variamos par?metros como a temperatura de deposi??o e a espessura dos filmes, com o prop?sito de dominar o processo de produ??o e reprodu??o de filmes nanoestruturados monocristalinos de Fe. Nesta s?rie de amostras foram realizadas medidas de MOKE, FMR, AFM e XPS, a fim de investigar suas propriedades magnetocristalinas e estruturais. Do ponto de vista magn?tico, os resultados de MOKE e FMR revelaram um crescimento da anisotropia magnetocristalina decorrente do aumento da temperatura. As medidas de AFM forneceram informa??es a respeito da espessura e rugosidade da superf?cie, enquanto que os resultados de XPS foram utilizados na an?lise da pureza da composi??o dos filmes. O melhor conjunto de par?metros foi utilizado na etapa seguinte, a investiga??o do efeito estrutural nas propriedades magn?ticas das multicamadas. Nesta etapa foram depositadas multicamadas compostas por filmes de Fe e Cr intercalados, seguindo seq??ncia de crescimento peri?dica e quasiperi?dica de Fibonacci, em substrato de MgO (100). O comportamento das curvas obtidas por MOKE e FMR e- videnciaram a presen?a do acoplamento de troca entre as camadas ferromagn?ticas. Atrav?s do ajuste computacional realizado para as curvas de magnetiza??o, foi poss?vel determinar a natureza e a intensidade da intera??o entre as camadas adjacentes de Fe. Ap?s minimizar numericamente a energia magn?tica total que descreve o comportamento do sistema, utiliza-se os ?ngulos de equil?brio para obter curvas de magnetiza??o e magnetoresist?ncia. O conjunto de resultados obtidos ao longo do desenvolvimento deste trabalho demonstram a efici?ncia e versatilidade da t?cnica de sputtering na s?ntese de filmes ultrafinos e multicamadas de alta qualidade. Permitindo inclusive a deposi??o de nanoestruturas magn?ticas que apresentaram patamares bem definidos de magnetiza??o e magnetoresist?ncia com possibilidade de aplica??o tecnol?gica
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Hernandez, Sarah Christine. "IInvestigation of Magnetostatics of Exchange-Coupled Nano-dots using the Magneto-optic Kerr Effect Technique." Miami University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=miami1249430747.
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Однодворець, Лариса Валентинівна, Лариса Валентиновна Однодворец, Larysa Valentynivna Odnodvorets, Олександр Валерійович Пилипенко, Александр Валериевич Пилипенко, Oleksandr Valeriiovych Pylypenko, Олена Петрівна Ткач, et al. "Electrophysical, Magnetoresistivity and Magneto-optical Properties of Multilayer Materials Based on Nanocrystalline and Amorphous Films." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35009.
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In work is presented to the results of complex investigate of phase formation, thermal resistivite, magnetoresistive
and magneto-optical properties of multilayers based Fe and Pd, Ag or Ge, which obtained by
sequential condensation of the layers with following thermal annealing. Investigation of phase formation
processes of thin film systems and established of correlation between this processes and above-mention
physical properties.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35009
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Tibaldi, Pier Silvio TIbaldi. "Flexible Time-Resolved Magneto-Optical Measurements." Thesis, Uppsala universitet, Materialfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-304296.
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We present a time-resolved Kerr microscope, capable of measuring the magnetization dynamics of samples grown on transparent, double-side-polished substrates.The magnetization is excited by a current pulse, using a coplanar waveguide placed beneath the samples. The Kerr rotation is detected with the stroboscopic pump-probe technique, using a probing laser, synchronized with the current pulse.We report benchmark measurements of the time-resolved Kerr instrument for magnetization dynamics in thin permalloy and FePd films. The experimental results for ferromagnetic resonance peaks have been compared with the values predicted by Kittel.Vi presenterar ett tidsupplöst Kerr-mikroskop, kapabel till att mäta magnetiseringsdynamiken hos magnetiska prov tillverkade på transparenta, dubbelsdigt polerade substrat. Magnetiseringen exiteras med en strömpuls via en koplanär vågguide placerad under provet. Kerr-rotationen detekteras med hjälp av en stroboskopisk ”pump-probe” teknik som använder en ”probing” laser synchroniserad med strömpulsen. Vi rapporterar prestandatest av det tidsupplösta kerr-instrumentet för magnetiseringsdynamiken i tunna permalloy - och FePd - filmer. De experimentella resultaten för de ferromagnetiska resonans-peakarna har jämförts med beräknade värden från Kittel.
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Zygridou, Smaragda. "Fabrication and characterisation of L10 ordered FePt thin films and bit patterned media." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/fabrication-and-characterisation-of-l10-ordered-fept-thin-films-and-bit-patterned-media(838fa936-fad2-422a-a1dc-ab852f77b6a6).html.
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Highly ordered magnetic materials with high perpendicular magnetic anisotropy (PMA), such as the L10 ordered FePt, and new recording technologies, such as bit patterned media (BPM), have been proposed as solutions to the media trilemma problem and provide promising strategies towards future high-density magnetic data storage media. L10 ordered FePt thin films can provide the necessary high PMA. However, the ordering of this material perpendicular to the plane of the films remains challenging since high-temperature and time-consuming processes are required. In this work, a remote plasma sputtering system has been used for the investigation of FePt thin films in order to understand if the greater control of process parameters offered by this system can lead to enhanced ordering in L10 FePt thin films at low temperatures compared with conventional dc magnetron approaches. More specifically, the effect of the different substrate temperatures and the target bias voltages on the ordering, the microstructure and the magnetic properties of FePt thin films was investigated. Highly ordered FePt thin films were successfully fabricated after post-annealing processes and were patterned into arrays of FePt islands. This patterning process was carried out with e-beam lithography and ion milling. Initial MFM measurements of these islands showed their single-domain structure for all the island sizes, which indicated the high PMA of the FePt. Magnetometry measurements were also carried out with a novel polar magneto-optical Kerr effect (MOKE) system which was designed and built during this project. This system has unique capabilities which are: a) the application of uniform magnetic field up to 2 Tesla, b) the rotation of the field to an arbitrary angle and c) the use of lasers of four different wavelengths. The combination of these abilities enabled measurements on ordered FePt thin films and patterned media which can pave the way for further highly sensitive measurements on magnetic thin films and nanostructures.
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Hernandez, Sarah Christine. "Investigation of magnetostatics of exchange-coupled nano-dots using the magneto-optic Kerr effect technique." Oxford, Ohio : Miami University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1249430747.
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Flajšman, Lukáš. "Vektorová Kerrova magnetometrie." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-232044.
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Increased complexity of novel magnetic materials in the last decade has placed high demands on the manufacturing process as well as on the characterization. One of the possibilities for characterization of magnetic samples is to exploit the magneto-optical effects. The presented work uses the magneto-optical Kerr effect as a major characterization technique to probe the magnetic properties of samples. We have developed a mathematical model describing the effect of the magnetization on the polarized light and present an apparatus capable of measuring the response given by the light-matter interaction. The experimental results show the performance of the apparatus on the various magnetic systems including meta-stable iron layers, Stoner-Wohlfarth particles and magnetic vortices. The scanning vectorial Kerr magnetometer allowed us to probe the vector of magnetization with diffraction limited resolution below 500 nm.
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Lee, Min-Sang [Verfasser], Hartmut [Gutachter] Zabel, and Daniel [Gutachter] Hägele. "Femtosekundenlaser-MOKE-Aufbau für räumlich und zeitlich aufgelöste Untersuchungen von Ummagnetisierungsprozessen und ultraschneller Magnetisierungsdynamik / Min-Sang Lee ; Gutachter: Hartmut Zabel, Daniel Hägele ; Fakultät für Physik und Astronomie." Bochum : Ruhr-Universität Bochum, 2015. http://d-nb.info/1236813340/34.
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Ahlberg, Martina. "Critical Phenomena and Exchange Coupling in Magnetic Heterostructures." Doctoral thesis, Uppsala universitet, Materialfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-168310.
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The continuous phase transition in thin magnetic films and superlattices has been studied using the magneto-optical Kerr effect (MOKE) and polarized neutron scattering (PNR). It has been shown that the critical behavior of amorphous thin films belonging to the 2D XY universality class can be described within the same theory as crystalline sample. This means that quenched disorder only serves as a marginal perturbation in systems with this symmetry. The connection between interlayer exchange coupling and the observed critical behavior in Fe/V superlattices was explored. The results prove that the origin of unusually high values of the exponent β can be traced to a position dependence of the magnetization at elevated temperatures. The magnetization of the outermost layers within the superlattice shows a more pronounced decrease at lower temperatures, compared to the inner layers, which in turn have a more abrupt decrease in the vicinity of the critical temperature. This translates to a high exponent, especially when the layers are probed by a technique where more weight is given to the layers close to the surface, e.g.MOKE. The interlayer exchange coupling as a function of spacer thickness and temperature was also studied in its own right. The data was compared to the literature, and a dependence on the thickness of the magnetic layers was concluded. The phase transition in amorphous FeZr/CoZr multilayers, where the magnetization emanates from ferromagnetic proximity effects, was investigated. Even though the determined exponents of the zero-field magnetization, the susceptibility and the critical isotherm did not correspond to any universality class, scaling plots displayed an excellent data collapse. Samples consisting of Fe δ-layers (0.3-1.4 monolayers) embedded in Pd were studied using element-specific resonant x-ray magnetic scattering. The magnetization of the two constituents showed distinctly different temperature dependences.
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CHINNI, Federico. "Hysteretic magnetic behavior of AuCo nanocomposite systems." Doctoral thesis, Università degli studi di Ferrara, 2018. http://hdl.handle.net/11392/2487888.
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Nowadays, the search for innovative nanocomposite systems consisting of at least two different magnetic phases is attracting remarkable attention. Indeed, the intimate mixing of the different phases at the nano scale level may give rise to new materials showing unique properties. In particular, a fine tuning of their overall magnetic anisotropy may be obtained and, accordingly, of their magnetic hysteretic properties.
In this framework, this thesis is dedicated to an in-depth study of the magnetic properties of AuCo nanostructures in form of both continuous films and Nano Holes Array (NHA) systems. The studied structures have been grown by magnetron sputtering co-deposition technique; method, which working far from the thermodynamic equilibrium, allows the alloying of Au and Co and the production of a bimetallic compound can be achieved to a good extent. Our samples mainly consist of a structurally disordered ferromagnetic alloy in which segregated Co nanoparticles are dispersed and the two phases are finely intermixed. The aim of this research is mainly focused on the magnetism of these AuCo nanocomposite structures in function of both the concentration ratio between the two metals and the thickness. In addition, the study highlights how the nanostructuring process affects the overall magnetic behavior. The magnetic properties of the studied AuCo nanostructures have been investigated from both an experimental point of view and a micromagnetic point of view.
Our magnetic analyses emphasize that the investigated systems must be treated as fully-fledged composite structures and the obtained results enlarge the knowledge on nanocomposite materials in the prespective to control their overall magnetic anisotropy and, hence, the magnetization reversal process.Oggigiorno, la ricerca di sistemi nanocompositi costituiti da almeno due fasi magnetiche sta suscitando una sempre maggiore attenzione. In effetti, l’intima miscelazione di due o più fasi magnetiche a livello nanometrico può dare origine a materiali che mostrano proprietà uniche. In particolare, è possibile raggiungere un accurato controllo della anisotropia complessiva del sistema e, di conseguenza, delle sue caratteristiche isteretiche. In questo contesto, questa tesi è dedicata ad un approfondito studio delle proprietà magnetiche di nano- strutture oro-cobalto (AuCo) sia in forma di film continui che di matrici periodiche nanostrutturate (Nano Holes Arrays). Le strutture in esame sono state cresciute grazie alla tecnica del co-sputtering; metodo che, lavorando lontano dalla condizione di equilibrio termodinamico, consente di ottenere una lega di Au e Co e la produzione di un composto bimetallico può essere raggiunta in buona misura. I campioni prodotti consistono principalmente di una lega ferromagnetica strutturalmente disordinata in cui sono disperse nanoparticelle di Co e le due fasi sono finemente mescolate. Lo scopo di questa ricerca è principalmente focalizzato sull’evoluzione delle proprietà magnetiche sia in funzione del rapporto di concentrazione tra i due metalli che dello spessore. Inoltre, lo studio evidenzia come il processo di nanostrutturazione influisca sul comportamento magnetico generale. La caratterizzione magnetica è stata condotta sia da un punto di vista sperimentale che da un punto di vista micromagnetico. I nostri studi sottolineano come i sistemi investigati debbano essere considerati struttute magnetiche nanocomposite a tutti gli effetti ed i risultati ottenuti ampliano la conoscenza su questa tipologia di mate- riali nella prospettiva di controllare la loro anisotropia magnetica e, quindi, il processo di inversione della magnetizzazione.
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Markó, Daniel. "Magnetostatics and Dynamics of Ion Irradiated NiFe/Ta Multilayer Films Studied by Vector Network Analyzer Ferromagnetic Resonance." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-64289.
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In the present work, the implications of ion irradiation on the magnetostatic and dynamic properties of soft magnetic Py/Ta (Py = Permalloy: Ni80Fe20) single and multilayer films have been investigated with the main objective of finding a way to determine their saturation magnetization. Both polar magneto-optical Kerr effect (MOKE) and vector network analyzer ferromagnetic resonance (VNA-FMR) measurements have proven to be suitable methods to determine µ0MS, circumventing the problem of the unknown effective magnetic volume that causes conventional techniques such as SQUID or VSM to fail. Provided there is no perpendicular anisotropy contribution in the samples, the saturation magnetization can be determined even in the case of strong interfacial mixing due to an inherently high number of Py/Ta interfaces and/or ion irradiation with high fluences. Another integral part of this work has been to construct a VNA-FMR spectrometer capable of performing both azimuthal and polar angle-dependent measurements using a magnet strong enough to saturate samples containing iron. Starting from scratch, this comprised numerous steps such as developing a suitable coplanar waveguide design, and writing the control, evaluation, and fitting software. With both increasing ion fluence and number of Py/Ta interfaces, a decrease of saturation magnetization has been observed. In the case of the 10×Py samples, an immediate decrease of µ0MS already sets in at small ion fluences. However, for the 1×Py and 5×Py samples, the saturation magnetization remains constant up to a certain ion fluence, but then starts to rapidly decrease. Ne ion irradiation causes a mixing and broadening of the interfaces. Thus, the Py/Ta stacks undergo a transition from being polycrystalline to amorphous at a critical fluence depending on the number of interfaces. The saturation magnetization is found to vanish at a Ta concentration of about 10–15 at.% in the Py layers. The samples possess a small uniaxial anisotropy, which remains virtually unaffected by the ion fluence, but slightly reduces with an increasing number of Py/Ta interfaces. In addition to magnetostatics, the dynamic properties of the samples have been investigated as well. The Gilbert damping parameter α increases with both increasing number of Py/Ta interfaces and higher ion fluences, with the former having a stronger influence. The inhomogeneous linewidth broadening ΔB0 increases as well with increasing number of Py/Ta interfaces, but slightly decreases for higher ion fluencesIn dieser Dissertation ist der Einfluss von Ionenbestrahlung auf die magnetostatischen und dynamischen Eigenschaften von weichmagnetischen Py/Ta-Einzel- und Multilagen (Py = Permalloy: Ni80Fe20) untersucht worden, wobei das Hauptziel gewesen ist, eine Methode zur Bestimmung der Sättigungsmagnetisierung zu finden. Sowohl polare magneto-optische Kerr-Effektmessungen (MOKE) als auch ferromagnetische Resonanzmessungen mittels eines Vektornetzwerkanalysators (VNA-FMR) haben sich als geeignet erwiesen, um µ0MS zu bestimmen, wobei das Problem des unbekannten effektiven magnetischen Volumens umgangen wird, welches bei der Verwendung von Techniken wie SQUID oder VSM auftreten würde. Unter der Voraussetzung, dass die Proben keinen senkrechten magnetischen Anisotropiebeitrag besitzen, kann die Sättigungsmagnetisierung selbst im Fall starker Grenzflächendurchmischung infolge einer großen Anzahl an Py/Ta-Grenzflächen und/oder Ionenbestrahlung mit hohen Fluenzen bestimmt werden. Ein weiterer wesentlicher Bestandteil dieser Arbeit ist die Konstruktion eines VNA-FMR-Spektrometers gewesen, welches vollautomatisiert ist, polare und azimutale Winkelabhängigkeiten messen kann und einen Magneten besitzt, der Proben, die Eisen beinhalten, sättigen kann. Von Grund auf beginnend umfasste dies zahlreiche Schritte wie z. B. die Entwicklung eines geeigneten koplanaren Wellenleiterdesigns sowie das Schreiben von Steuerungs-, Auswertungs- und Fitprogrammen. Mit steigender Fluenz und Zahl an Py/Ta-Grenzflächen ist eine Abnahme der Sättigungsmagnetisierung beobachtet worden. Im Fall der 10×Py-Proben findet diese bereits bei kleinen Fluenzen statt. Im Gegensatz dazu bleibt µ0MS der 1×Py- und 5×Py-Proben bis zu einer bestimmten Fluenz konstant, bevor sie sich dann umso schneller verringert. Die Bestrahlung mit Ne-Ionen verursacht eine Durchmischung und Verbreiterung der Grenzflächen. Infolgedessen erfahren die Py/Ta-Proben bei einer kritischen Fluenz, die von der Zahl der Grenzflächen abhängig ist, einen Phasenübergang von polykristallin zu amorph. Die Sättigungsmagnetisierung verschwindet ab einer Ta-Konzentration von etwa 10–15 Atom-% in den Py-Schichten. Die Proben besitzen eine kleine uniaxiale Anisotropie, die praktisch unbeeinflusst von der Fluenz ist, sich jedoch mit steigender Zahl an Py/Ta-Grenzflächen leicht verringert. Neben den statischen sind auch die dynamischen magnetischen Eigenschaften der Proben untersucht worden. Der Gilbert-Dämpfungsparameter α erhöht sich sowohl mit steigender Zahl an Py/Ta-Grenzflächen als auch mit höheren Fluenzen, wobei Erstere einen größeren Einfluss hat. Die inhomogene Linienverbreiterung ΔB0 nimmt ebenfalls mit steigender Zahl an Py/Ta-Grenzflächen zu, verringert sich jedoch bei größeren Fluenzen leicht
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Pincelli, T. "PROBING ELECTRON CORRELATION DYNAMICS: A MULTI-TECHNIQUE STUDY APPLIED TO THE HALF-METALLIC OXIDE LA1-XSRXMNO3." Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/543731.
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This thesis completes my work as doctoral student of the Scuola di Dottorato in Fisica, Astrofisica e Fisica Applicata at the Università degli Studi di Milano that has been carried out, starting in November 2014, mostly at the Laboratorio TASC of IOM-CNR in the premises of the Elettra - Sincrotrone Trieste and FERMI@Elettra infrastructures, in the framework of the NFFA and APE-beamline facilites, as well as by accessing international large scale infrastructures and laboratories.
The activity has addressed the development of experimental methodologies and novel instrumentation oriented to the study of the dynamical properties of highly correlated materials after high energy excitation. The science programme has been carried out by exploiting ultrafast femtosecond probes from the optical regime (Ti-Sa lasers, fibre laser oscillators) to the extreme UV-soft X rays at FERMI, to the picosecond hard X-rays from the SPring-8 and Diamond synchrotron radiation source. The sample synthesis of correlated oxides and its characterization has been performed within the NFFA facility and APE-group collaboration in Trieste as well as the design and construction of the all new laser High Harmonic Generation beam line NFFA-SPRINT and its end station for time resolved vectorial electron spin polarimetry.
This report concentrates on the main scientific concern of my work that has been the relaxation of external perturbations in a correlated electron material both in the time and space domain.
I have employed Photoelectron Spectroscopy (PES) mostly in the Hard X-ray regime (HAXPES), pushing the boundaries of its application to achieve a coherent perspective. The material I have mainly focused on is La0.67Sr0.33MnO3 (LSMO), of high interest for spintronics. This system is prototypical, yielding the highest simplicity in the class of transition metal oxides.
In the spatial investigation, I have controlled with high precision the PES probing depth and I have observed the evolution of one spectral feature. I have identified it as probe of electronic hybridization and long-range ordering. I have studied LSMO films of 40 nm in three substrate-induced strain states (1% tensile in-plane, relaxed, 1% compressive in-plane) and a 18 nm film of (Ga,Mn)As (GMA), a well-studied diluted magnetic semiconductor. I have found that the electronic properties to be modified at significant distances from the surface, 4 nm for LSMO and 1.2 nm for GMA, while strain had no detectable effects.
In the temporal study, I have employed HAXPES in pump-probe mode (TR-HAXPES) to observe the evolution of the electronic structure after intense optical excitation. A detailed dynamical characterization with optical techniques has allowed me to identify the characteristic time of the collapse of long-range magnetic order to be significantly longer than the one of elemental transition metals. I have ascribed this effect to the half-metallic character of LSMO. With TR-HAXPES I have observed that the whole electronic band-structure evolution is bottlenecked by the slow response of the magnetization, proceeding on hundreds of picoseconds timescales.
Finally, I have described the techniques and the instrumentation that can be used to push these investigations to shorter spatial and temporal scales. This has been realized in the form of the NFFA-SPRINT laboratory, a facility open to users, which I participated in designing and developing.
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Will, Iain Gordon. "Development of a UHV MBE growth facility with in-situ MOKE and strain-dependent magnetometry and its application to ultra-thin Co and Fe films grown on GaAs(100) and InAs/GaAs(100) substrates." Thesis, University of York, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542820.
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Ball, David Klaus. "From 2D CoCrPt:SiO2 films with perpendicular magnetic anisotropy to 3D nanocones — A step towards bit patterned media —." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-113029.
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Due to the ever-increasing worldwide consumption of memory for digital information, new technologies for higher capacity and faster data storage systems have been the focus of research and development. A step towards achieving higher data storage densities or magnetic recording media is the concept of bit patterned media, where the magnetic recording layer is divided up into magnetically isolated bit units. This approach is one of the most promising technologies for increasing data storage densities and could be implemented by nanostructuring the wafer. Therefore, the fabrication of the appropriate nanostructures on a small scale and then be able to manufacture these structures on an industrial scale is one of the problems where science and industry are working on a solution. In addition, the answer to the open question about the influence that patterning on the nano length scale has on the magnetic properties is of great interest. The main goal of this thesis is to answer the open question, which magnetic properties can be tailored by a modification of the surface texture on the nanometre length scale. For this purpose the following properties: anisotropy, remanence, coercivity, switching field distribution, saturation magnetisation, Gilbert damping, and inhomogeneous linebroadening were compared between planar two dimensional thin ferromagnetic films and three dimensional magnetic structures. In addition, the influences of the tailored morphology on the intergranular or the exchange coupling between the structures, which is called interdot exchange coupling, was investigated. For the ferromagnetic thin films, the focus of the investigations was on the granular CoCrPt:SiO2 and [Co/Pd] layer, which currently are the state-of-the-art material for magnetic data storage media. These materials are characterised by their high coercivity and high perpendicular anisotropy, which has a low spatial distribution in the preferred direction of magnetisation. In this work the pre-structured GaSb(001) substrate with self-assembled periodic nanocone structures at the surface are used. The preparation by ion beam erosion of these structures is simple, fast, and highly reproducible and therefore this method is particularly beneficial for fundamental research. To compare the 2D thin films with the 3D magnetic structures, besides the pre-structured specimen, planar samples were also fabricated. The first sample series prepared was coated by Py. Due to the fact that the magnetic properties of this material are well-known, it was also possible to do some OOMMF simulations in addition to the VNA-FMR and MOKE measurements. Afterwards two planar samples with CoCrPt and CoCrPt:SiO2 were prepared. The planar CoCrPt:SiO2 samples were Co+ ion implanted to study the influence of such irradiation on the intergranular and interdot exchange coupling, switching field distribution, and in particular on the spin dynamics. Moreover, both samples were measured by TRMOKE in order to obtain information about the spin dynamics. Subsequently, the perpendicular storage media materials CoCrPt:SiO2 and [Co/Pd] were deposited on a prestructured GaSb(001) nanocone substrate surface. These sample series were measured by MOKE, SQUID, and vector-VSM. The measurements demonstrate the influence of the periodicity and height of the nanocones on the intergranular and interdot exchange coupling. They also show the reorientation of the magnetisation with respect to the curvature of the substrate template and furthermore, the morphology-induced influences on the magnetic domains. From the comparison between the results for the planar and the pre-structured samples, a decrease of the interdot exchange coupling was observed, which scales together with the periodicity of the nanocone pattern. In addition, it was shown that for all samples with thin magnetic films on nanocones,the magnetisation aligns along the curvature of the underlying nanocone structure. For Py on nanocones, planar granular CoCrPt:SiO2, and planar granular CoCrPt, measurements by VNA-FMR and TRMOKE could be carried out, which yielded information about the spin dynamics. The results obtained for both of the planar sample are comparable to values from the literature for the Gilbert damping. The results for the Py samples showed that the commonly used 2D model resonance condition is, in case of a 3D magnetic structure, no longer valid due to the alignment of the magnetisation along the underlying substrate structure and therefore an new model has to be derivedAufgrund des weltweiten, immer weiter steigenden Bedarfs an Speicherplatz von digitalen Information, sind neue Technologien für größere und schnellere Speichermedien im Fokus von Forschung und Entwicklung. Ein Schritt hin zu einer höheren Speicherdichte in der magnetischen Datenspeicherung ist dabei das sogenannte Konzept der ”Bit patterned media”, das definierte Informationseinheiten auf regelmäßig angeordneten Nanostrukturen beschreibt. Dieser Ansatz ist einer der derzeit vielversprechendsten Optionen die Speicherdichte zu erhöhen. Dabei ist die Herstellung der benötigten Nanostrukturen und deren Skalierung hin zu makroskopischen Dimensionen eines der Probleme an deren Lösung die Wissenschaft und Industrie derzeit arbeitet. Desweiteren ist die Antwort auf die noch offene Frage nach der Beeinflussung der nanoskaligen Strukturen auf die magnetischen Eigenschaften von großem Interesse. Das Hauptziel in dieser Arbeit ist es, einen Beitrag zur Beantwortung der Frage, welche magnetischen Eigenschaften sich durch eine Veränderung der Oberflächenstruktur im Nanometerbereich beeinflussen lassen, zu leisten. Hierzu wurden die folgenden Eigenschaften, wie zum Beispiel die Anisotropie, Remanenz,Koerzitivität, Schaltfeldverteilung, Sättigungsmagnetisierung, Gilbertdämpfung und inhomogene Linienverbreiterung von planaren zweidimensionalen dünnen ferromagnetische Schichten mit denen von dreidimensionalen magnetischen Strukturen verglichen. Zusätzlich wurde der Einfluss der angegpassten Morphologie auf die intergranularen- beziehungsweise auf die zwischen den Strukturen wirkende (interdot) Austauschkopplung untersucht. Der Hauptaugenmerk bei den ferromagnetisch dünnen Schichten lag dabei auf den granularen CoCrPt:SiO2 und [Co/Pd] Filmen, die heutzutage ein Standardmaterial für die magnetischen Speichermedien darstellen. Diese Materialien zeichnen sich durch eine hohe Koerzivität und senkrechte Anisotropie, mit geringer räumlicher Verteilung der Vorzugsrichtung der Magnetisierung, aus. Die hier vorgestellten vorstrukturierten GaSb(001) Substrate mit selbstordnenden periodischen Nanokegeln auf der Oberfläche, sind mittels Ionenstrahlerosion einfach, schnell und sehr gut reproduzierbar herzustellen. Deshalb ist diese Methode besonders für die Grundlagenforschung von Vorteil. Um einen Vergleich zwischen 2D Filmen und 3D Strukturen ziehen zu können, wurden neben den vorstrukturierten Substraten auch planare Proben beschichtet. Eine erste Versuchsreihe wurde mit einem dünnen Py Film präpariert. Da dessen magnetische Eigenschaften wohlbekannt sind, konnten neben den Untersuchungen mit VNA-FMR und MOKE auch einige OOMF Simulationen erstellt werden. Danach wurden zwei Proben mit planarem CoCrPt beziehungsweise CoCrPt:SiO2 untersucht. Bei den planaren CoCrPt:SiO2 Proben wurden außerdem noch Co+ Ionen implantiert, um deren Auswirkungen auf die intergranulare Austauschkopplung, Schaltfeldverteilung und besonders auf die Spindynamik zu bestimmen. Bei beiden Probensystemen konnte zusätzlich die Spindynamik mittels zeitaufgelöstem MOKE gemessen werden. Im Anschluss wurden die beiden senkrechten Speichermedien CoCrPt:SiO2 and [Co/Pd] auf Substraten mit Nanokegeln vorstrukturierten GaSb(001) Oberflächen abgeschieden. Diese Proben wurden mit MFM, MOKE, SQUID und Vektor-VSM vermessen. Aus den Messungen konnnten dann die Einflüsse auf die intergranulare- beziehungsweise interdot Austauschkopplung in Abhängigkeit von der Periodizität und Höhe der Nanokegel bestimmt werden, sowie die Umorientierung der Magnetisierung bezüglich der Substratkrümmung und den Morphologie induzierten Einfluss auf die magnetischen Domänen. Anhand der Vergleiche zwischen den Messungen der planaren und den vorstrukturierten Proben konnte eine Verringerung der Austauschkopplung zwischen den Strukturen gezeigt werden, die mit der Nanokegelstrukturperiodizität skaliert. Außerdem wurde in allen dünnen magnetischen Filmen auf Nanokegeln gezeigt, dass die Magnetisierung sich in Abhängigkeit der darunterliegenden Struktur ausrichtet. Bei den Py auf Nanokegeln, den planaren CoCrPt und dem planaren CoCrPt:SiO2 Proben konnten außerdem mit VNA-FMR und TRMOKE Informationen bezüglich der Spindynamik gemessen werden. Die erzielten Ergebnisse, der beiden planaren Proben, sind vergleichbar mit denen, aus der Literatur bekannten Werten, für die Gilbertdämpfung. Darüber hinaus wurde durch die Messungen an den Py Proben gezeigt, dass die Theorie, des bisher genutzten 2D Modells, nicht mehr gültig ist, da sich die Magnetisierung entlang der Substratstruktur ausrichtet, und deshalb ein neues Model aufgestellt werden muss
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Ball, David Klaus. "From 2D CoCrPt:SiO2 films with perpendicular magnetic anisotropy to 3D nanocones — A step towards bit patterned media —." Doctoral thesis, Helmholtz-Zentrum Dresden-Rossendorf, 2012. https://tud.qucosa.de/id/qucosa%3A26882.
Full textAbstract:
Due to the ever-increasing worldwide consumption of memory for digital information, new technologies for higher capacity and faster data storage systems have been the focus of research and development. A step towards achieving higher data storage densities or magnetic recording media is the concept of bit patterned media, where the magnetic recording layer is divided up into magnetically isolated bit units. This approach is one of the most promising technologies for increasing data storage densities and could be implemented by nanostructuring the wafer. Therefore, the fabrication of the appropriate nanostructures on a small scale and then be able to manufacture these structures on an industrial scale is one of the problems where science and industry are working on a solution. In addition, the answer to the open question about the influence that patterning on the nano length scale has on the magnetic properties is of great interest.
The main goal of this thesis is to answer the open question, which magnetic properties can be tailored by a modification of the surface texture on the nanometre length scale. For this purpose the following properties: anisotropy, remanence, coercivity, switching field distribution, saturation magnetisation, Gilbert damping, and inhomogeneous linebroadening were compared between planar two dimensional thin ferromagnetic films and three dimensional magnetic structures. In addition, the influences of the tailored morphology on the intergranular or the exchange coupling between the structures, which is called interdot exchange coupling, was investigated. For the ferromagnetic thin films, the focus of the investigations was on the granular CoCrPt:SiO2 and [Co/Pd] layer, which currently are the state-of-the-art material for magnetic data storage media. These materials are characterised by their high coercivity and high perpendicular anisotropy, which has a low spatial distribution in the preferred direction of magnetisation.
In this work the pre-structured GaSb(001) substrate with self-assembled periodic nanocone structures at the surface are used. The preparation by ion beam erosion of these structures is simple, fast, and highly reproducible and therefore this method is particularly beneficial for fundamental research. To compare the 2D thin films with the 3D magnetic structures, besides the pre-structured specimen, planar samples were also fabricated. The first sample series prepared was coated by Py. Due to the fact that the magnetic properties of this material are well-known, it was also possible to do some OOMMF simulations in addition to the VNA-FMR and MOKE measurements.
Afterwards two planar samples with CoCrPt and CoCrPt:SiO2 were prepared. The planar CoCrPt:SiO2 samples were Co+ ion implanted to study the influence of such irradiation on the intergranular and interdot exchange coupling, switching field distribution, and in particular on the spin dynamics. Moreover, both samples were measured by TRMOKE in order to obtain information about the spin dynamics.
Subsequently, the perpendicular storage media materials CoCrPt:SiO2 and [Co/Pd] were deposited on a prestructured GaSb(001) nanocone substrate surface. These sample series were measured by MOKE, SQUID, and vector-VSM. The measurements demonstrate the influence of the periodicity and height of the nanocones on the intergranular and interdot exchange coupling. They also show the reorientation of the magnetisation with respect to the curvature of the substrate template and furthermore, the morphology-induced influences on the magnetic domains.
From the comparison between the results for the planar and the pre-structured samples, a decrease of the interdot exchange coupling was observed, which scales together with the periodicity of the nanocone pattern. In addition, it was shown that for all samples with thin magnetic films on nanocones,the magnetisation aligns along the curvature of the underlying nanocone structure. For Py on nanocones, planar granular CoCrPt:SiO2, and planar granular CoCrPt, measurements by VNA-FMR and TRMOKE could be carried out, which yielded information about the spin dynamics. The results obtained for both of the planar sample are comparable to values from the literature for the Gilbert damping. The results for the Py samples showed that the commonly used 2D model resonance condition is, in case of a 3D magnetic structure, no longer valid due to the alignment of the magnetisation along the underlying substrate structure and therefore an new model has to be derived.Aufgrund des weltweiten, immer weiter steigenden Bedarfs an Speicherplatz von digitalen Information, sind neue Technologien für größere und schnellere Speichermedien im Fokus von Forschung und Entwicklung. Ein Schritt hin zu einer höheren Speicherdichte in der magnetischen Datenspeicherung ist dabei das sogenannte Konzept der ”Bit patterned media”, das definierte Informationseinheiten auf regelmäßig angeordneten Nanostrukturen beschreibt. Dieser Ansatz ist einer der derzeit vielversprechendsten Optionen die Speicherdichte zu erhöhen. Dabei ist die Herstellung der benötigten Nanostrukturen und deren Skalierung hin zu makroskopischen Dimensionen eines der Probleme an deren Lösung die Wissenschaft und Industrie derzeit arbeitet. Desweiteren ist die Antwort auf die noch offene Frage nach der Beeinflussung der nanoskaligen Strukturen auf die magnetischen Eigenschaften von großem Interesse. Das Hauptziel in dieser Arbeit ist es, einen Beitrag zur Beantwortung der Frage, welche magnetischen Eigenschaften sich durch eine Veränderung der Oberflächenstruktur im Nanometerbereich beeinflussen lassen, zu leisten. Hierzu wurden die folgenden Eigenschaften, wie zum Beispiel die Anisotropie, Remanenz,Koerzitivität, Schaltfeldverteilung, Sättigungsmagnetisierung, Gilbertdämpfung und inhomogene Linienverbreiterung von planaren zweidimensionalen dünnen ferromagnetische Schichten mit denen von dreidimensionalen magnetischen Strukturen verglichen. Zusätzlich wurde der Einfluss der angegpassten Morphologie auf die intergranularen- beziehungsweise auf die zwischen den Strukturen wirkende (interdot) Austauschkopplung untersucht. Der Hauptaugenmerk bei den ferromagnetisch dünnen Schichten lag dabei auf den granularen CoCrPt:SiO2 und [Co/Pd] Filmen, die heutzutage ein Standardmaterial für die magnetischen Speichermedien darstellen. Diese Materialien zeichnen sich durch eine hohe Koerzivität und senkrechte Anisotropie, mit geringer räumlicher Verteilung der Vorzugsrichtung der Magnetisierung, aus. Die hier vorgestellten vorstrukturierten GaSb(001) Substrate mit selbstordnenden periodischen Nanokegeln auf der Oberfläche, sind mittels Ionenstrahlerosion einfach, schnell und sehr gut reproduzierbar herzustellen. Deshalb ist diese Methode besonders für die Grundlagenforschung von Vorteil. Um einen Vergleich zwischen 2D Filmen und 3D Strukturen ziehen zu können, wurden neben den vorstrukturierten Substraten auch planare Proben beschichtet. Eine erste Versuchsreihe wurde mit einem dünnen Py Film präpariert. Da dessen magnetische Eigenschaften wohlbekannt sind, konnten neben den Untersuchungen mit VNA-FMR und MOKE auch einige OOMF Simulationen erstellt werden. Danach wurden zwei Proben mit planarem CoCrPt beziehungsweise CoCrPt:SiO2 untersucht. Bei den planaren CoCrPt:SiO2 Proben wurden außerdem noch Co+ Ionen implantiert, um deren Auswirkungen auf die intergranulare Austauschkopplung, Schaltfeldverteilung und besonders auf die Spindynamik zu bestimmen. Bei beiden Probensystemen konnte zusätzlich die Spindynamik mittels zeitaufgelöstem MOKE gemessen werden. Im Anschluss wurden die beiden senkrechten Speichermedien CoCrPt:SiO2 and [Co/Pd] auf Substraten mit Nanokegeln vorstrukturierten GaSb(001) Oberflächen abgeschieden. Diese Proben wurden mit MFM, MOKE, SQUID und Vektor-VSM vermessen. Aus den Messungen konnnten dann die Einflüsse auf die intergranulare- beziehungsweise interdot Austauschkopplung in Abhängigkeit von der Periodizität und Höhe der Nanokegel bestimmt werden, sowie die Umorientierung der Magnetisierung bezüglich der Substratkrümmung und den Morphologie induzierten Einfluss auf die magnetischen Domänen. Anhand der Vergleiche zwischen den Messungen der planaren und den vorstrukturierten Proben konnte eine Verringerung der Austauschkopplung zwischen den Strukturen gezeigt werden, die mit der Nanokegelstrukturperiodizität skaliert. Außerdem wurde in allen dünnen magnetischen Filmen auf Nanokegeln gezeigt, dass die Magnetisierung sich in Abhängigkeit der darunterliegenden Struktur ausrichtet. Bei den Py auf Nanokegeln, den planaren CoCrPt und dem planaren CoCrPt:SiO2 Proben konnten außerdem mit VNA-FMR und TRMOKE Informationen bezüglich der Spindynamik gemessen werden. Die erzielten Ergebnisse, der beiden planaren Proben, sind vergleichbar mit denen, aus der Literatur bekannten Werten, für die Gilbertdämpfung. Darüber hinaus wurde durch die Messungen an den Py Proben gezeigt, dass die Theorie, des bisher genutzten 2D Modells, nicht mehr gültig ist, da sich die Magnetisierung entlang der Substratstruktur ausrichtet, und deshalb ein neues Model aufgestellt werden muss.
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Webb, Justin. "Physical activity behaviour change : supporting cancer survivors to move more." Thesis, University of Surrey, 2018. http://epubs.surrey.ac.uk/850020/.
Full textAbstract:
This thesis is presented in five chapters. Chapter one offers a review of the literature, divided into six sections. The first section of this chapter provides an understanding of cancer as a disease and a public health concern, including detail on its incidence and prevalence, the biology of cancer and its treatment. The second section of this chapter reviews the literature on physical activity and cancer across the cancer continuum, from prevention of cancer, through cancer treatment, living with or beyond cancer, advanced cancer, and detail on physical activity and cancer mortality and recurrence. The third section of this chapter discusses the determinants of physical activity in cancer survivors, framed within behavioural theories and models to support the identification of intervention opportunities. The identified intervention opportunities are covered in the fourth section. The fifth section of this chapter presents the scope and relevance of the research included in this thesis. The sixth section provides a summary of chapter one. Chapter two presents the first study included within this thesis, a service evaluation investigating the reach, adoption, and impact of a training intervention to influence UK healthcare professionals to give very brief advice on physical activity to cancer survivors. This study also includes an assessment of the predictive value of the behavioural theory upon which the intervention is based, the COM-B model of behaviour (Michie, van Stralen, & West, 2011). Chapter two includes four sections covering an introduction, the method, results, and discussion. Chapter three presents the second study within this thesis. The second study is a randomised waiting list control trial to investigate the impacts of a remote-print based intervention supported by Internet-based tools on the physical activity, self-efficacy, and health-related quality of life (HRQOL) of cancer survivors. The randomised waiting list control trial also includes a cost-consequence analysis. Chapter four presents the third study of this thesis, a process evaluation of the remote-print based intervention supported by Internet-based tools. This process evaluation aimed to contextualise use and perceived usefulness of the intervention, supporting the identification of what works and for whom. Chapter five then closes this thesis with a discussion on the theoretical and practical contributions of the body of research as a whole. This final chapter also includes discussion on how the interventions under assessment influence the identified determinants of physical activity in cancer survivors, and identification of future research possibilities.
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Besbas, Jean. "Influence de la densité de trous sur la dynamique des charges et de l'aimantation du (Ga, Mn)As en couche." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00798208.
Full textAbstract:
Ce travail étudie le rôle de la densité de trous à l'équilibre sur la dynamique des charges et de la norme de l'aimantation de (Ga,Mn)As pour des densités de manganèse et d'impuretés fixées indépendamment. Des expériences " pompe-sonde " mettent en relation les dynamiques de réflectivité et d'angle de rotation Kerr. Deux relaxations sont mises en évidence. La première traduit un échauffement variable du gaz de trous entre 1ps et 100ps. La seconde traduit une diffusion-recombinaison des charges entre 100ps et 1500ps et évolue en fonction du rapport entre extension spatiale d'états d'impuretés, piégeant les électrons photo générés, et vitesse de Fermi. Pour compléter l'approche, une étude numérique de l'état fondamental des échantillons par la théorie de la fonctionnelle de la densité relie aimantation, température et densité de trous. Elle interprète la dynamique de la norme de l'aimantation à partir d'un diagramme de phase statique correspondant aux données publiées pour (Ga,Mn)As, qui est fonction de la température et de la densité de trous. Cette dynamique se ramène à celle de la réflectivité. Ceci permet de préciser les contributions de la norme et de l'orientation de l'aimantation dans le signal dynamique de rotation Kerr.
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Макуха, Зінаїда Миколаївна, Зинаида Николаевна Макуха, and Zinaida Mykolaivna Makukha. "Магнітодеформаційний ефект у плівкових матеріалах на основі феромагнітних і немагнітних металів." Thesis, Сумський державний університет, 2016. http://essuir.sumdu.edu.ua/handle/123456789/44626.
Full textAbstract:
Дисертацію присвячено комплексному дослідженню структурно-фазового стану, тензорезистивних і магнітодеформаційних властивостей в коефіцієнті тензочутливості та МОКЕ плівок на основі феромагнітних (Co, Fe) і немагнітних (Cu, Ag, Au, Pt) металів.
Установлено, що в магнітному полі спостерігається тенденція як до зростання, так і до спадання КТ в залежності від інтервалу деформації та типу досліджуваної плівки, в порівнянні з КТ при деформації за відсутності магнітного поля. Для одношарових плівок Со, здеформованих в області пластичності, КТ зростає на 25 %, а в області пружності - зменшується на 22 %. Двошарові плівкові системи Сo/Cu (Δεl = (0 - 0,4) %) та Co/Ag (Δεl = (0 - 2) %) характеризуються додатнім магнітодеформаційним ефектом.
Проведено дослідження магнітодеформаційного ефекту в МОКЕ. Встановлено, що деформація зразків призводить до зміни коерцитивності та кута повороту Керра. Зокрема, в поперечній геометрії вимірювання коерцитивна сила зростає у плівках Co/Au, та зменшується у плівках Со, Co/Cu. Fe/Pt
Запропоновано феноменологічну модель магнітодеформаційного ефекту в опорі для двошарових плівкових систем, яка дозволила розрахувати величину тензометричної характеристики.Диссертация посвящена комплексному исследованию структурно-фазового состояния, тензорезистивных и магнитодеформационных свойств в коэффициенте тензочувствительности и МОКЭ пленок на основе ферромагнитних (Сo, Fe) и немагнитных (Cu, Ag, Au, Pt) металлов. Установлено, что в магнитном поле наблюдается тенденция, как к возрастанию, так и к уменьшению КТ в зависимости от интервала деформации образцов и типа исследованной пленки, по сравнению с КТ при деформации при отсутствии магнитного поля. Для однослойных пленок Со, сдеформированных в области пластичности величина КТ возрастает на 25%, а в области упругости – уменьшается на 22%. Среднее значение магнитного коэффициента тензочувствительности в упругом интервале деформации = -7,4 Тл-1, а в пластическом - = 8,3 Тл-1 . Двухслойные пленочные системы Co/Cu (Δεl = (0 - 0,4) %) и Co/Ag (Δεl = (0 - 2) %) характеризуются положительным магнитодеформационным эффектом. Магнитодеформационные свойства в двухслойных пленках проявляются лучше, чем в однослойных, о чем можно судить из величины среднего значения МККТ, которая для системы Co/Cu равна 12 Тл-1, а для системы Co/Ag – 13,5 Тл-1. Кроме того, следует отметить, что в области пластичности с ростом толщины образцов наблюдается увеличение значения коэффициента тензочувствительности в процессе продольной деформации, что связано з усилением зернограничного рассеивания электронов и увеличением чувствительности к деформации. Проведены исследования магнитодеформационного эффекта в МОКЭ. Установлено, что деформация образцов приводит к изменению коэрцитивной силы и кута поворота Керра. В частности, в поперечной геометрии измерения коэрцитивная сила увеличивается для пленок Co/Au, и уменьшается для пленок Co, Co/Cu, Fe/Pt. Деформация образцов приводит к уменьшению угла поворота Керра, что объясняется уменьшением (дроблением) доменов в процессе приложения растягивающей деформации. Предложено феноменологическую модель магнитодеформационного эффекта в коэффициенте тензочувствительности для двухслойных пленочных систем, в рамках которой в общем виде проанализирована зависимость коэффициента тензочувствительности от величины магнитного поля. Произведен расчёт тензометрической характеристики, по величине которой можно судить о влиянии на удельное сопротивление одновременно двух факторов: деформации и магнитного. Были исследованы однослойные пленки и двухслойные пленочные системы типа «бипластина» или твердый раствор. Установлено, что основную роль играет общеая толщина пленочной системы, а не толщина отдельных слоев системы или концентрация атомов компонент.
The thesis is devoted to complex research of phase and structural state, strain and magnetostrain properties in strain coefficient and MOKE of films based on ferromagnetic (Co, Fe) and nonmagnetic (Cu, Ag, Au, Pt) metals. It was found, that in magnetic field the tendency to increase or decrease strain coefficient is observed as compared with strain coefficient measured in conditions of a magnetic field absence. It is depend on strain interval and the type of studing film. For single-layer films the strain coefficient increases to 25 % in the plastic range and decreases to 22 % in the elastic range. Two-layers films system Co/Cu (Δεl = (0 - 0,4) %) and Co/Ag (Δεl = (0 - 2) %) are characterized by a positive magnetostrain effect. The research of magnetostrain effect in MOKE was carried out. It was found, that the deformation of the samples causes a change in coercivity and Kerr rotation angle. In particular, in transverse geometry measurement the coercive force is increasing in the films Co/Au. The coercive force is decreasing in the films Co, Co/Cu and Fe/Pt. A phenomenological model magnetostrain effect in support for bilayer film systems that allowed to calculate the value of gauge characteristics.
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Fang, Lei. "Exploring spin in novel materials and systems." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1299611695.
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Burkert, Till. "Materials for Magnetic Recording Applications." Doctoral thesis, Uppsala University, Department of Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5800.
Full textAbstract:
In the first part of this work, the influence of hydrogen on the structural and magnetic properties of Fe/V(001) superlattices was studied. The local structure of the vanadium-hydride layers was determined by extended x-ray absorption fine structure (EXAFS) measurements. The magnetic ordering in a weakly coupled Fe/V(001) superlattice was investigated using the magneto-optical Kerr effect (MOKE). The interlayer exchange coupling is weakened upon alloying with hydrogen and a phase with short-range magnetic order was observed.
The second part is concerned with first-principles calculations of magnetic materials, with a focus on magnetic recording applications. The uniaxial magnetic anisotropy energy (MAE) of Fe, Co, and Ni was calculated for tetragonal and trigonal structures. Based on an analysis of the electronic states of tetragonal Fe and Co at the center of the Brillouin zone, tetragonal Fe-Co alloys were proposed as a material that combines a large uniaxial MAE with a large saturation magnetization. This was confirmed by experimental studies on (Fe,Co)/Pt superlattices. The large uniaxial MAE of L10 FePt is caused by the large spin-orbit interaction on the Pt sites in connection with a strong hybridization between Fe and Pt. Furthermore, it was shown that the uniaxial MAE can be increased by alloying the Fe sublattice with Mn. The combination of the high-moment rare-earth (RE) metals with the high-TC 3d transition metals in RE/Cr/Fe multilayers (RE = Gd, Tb, Dy) gives rise to a strong ferromagnetic effective exchange interaction between the Fe layers and the RE layer. The MAE of hcp Gd was found to have two principal contributions, namely the dipole interaction of the large localized 4f spins and the band electron magnetic anisotropy due to the spin-orbit interaction. The peculiar temperature dependence of the easy axis of magnetization was reproduced on a qualitative level.
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Bergeard, Nicolas. "Matériaux magnétiques pour l'étude de la dynamique de l'aimantation." Phd thesis, Paris 11, 2010. http://www.theses.fr/2010PA112271.
Full textAbstract:
Les alliages entre terres rares et métaux de transition CoGd possèdent des propriétés magnétiques uniques, qui en font des systèmes intéressants pour l'étude de la dynamique ultrarapide de l'aimantation ainsi que pour tester les mécanismes du transfert de spin. Pour expliquer la grande diversité des propriétés magnétiques observées dans ces alliages, une caractérisation fine des propriétés structurales est indispensable. Pour cela, j'ai développé une chambre de dépôt en ultra vide pour produire des couches minces d'alliage par coévaporation. Par absorption (EXAFS) et spectroscopie de photoélectrons (XPS), j'ai pu montrer la nature amorphe des alliages et la ségrégation d'une monocouche de gadolinium en surface. Par effet Kerr magnéto-optique et dichroïsme magnétique en absorption (XMCD), j'ai montré que les films présentent une anisotropie uni axiale dans le plan et, avec la composition ad-hoc, une paroi de compensation. J'ai étudié l'évolution thermique de l'aimantation des sous réseaux de Co et Gd, reproduite par des simulations issues d'un modèle de champ moyen. Les films ultra minces Pt/Co(5Å)/Pt présentent une anisotropie perpendiculaire au plan de la couche. Lorsque cette anisotropie et l'anisotropie dipolaire, qui ramène l'aimantation dans le plan de la couche, sont du même ordre de grandeur, une transition de réorientation de spin (SRT) se produit, associée au passage de l'aimantation hors du plan vers le plan. Dans Pt/Co(5Å)/Pt, j'ai étudié ce mécanisme de réorientation de l'aimantation ainsi que le régime de fluctuations lentes associé, lorsque l'anisotropie est pilotée finement par irradiation ioniqueRare earth transition metal alloys display unusual magnetic properties, which make them interesting systems to study ultrafast magnetization dynamic and to test mechanisms underlying spin torque. Diversity of magnetic properties observed in such alloys is bound to the lack of fine knowledge about their structural properties. I developed an ultra high vacuum chamber for deposition of thin alloys layers. Using absorption (EXAFS) and photoelectron spectroscopy (XPS), I put in evidence the amorphous structure of the alloys and the presence of a monolayer of Gd segregated at the surface. Using magneto-optical Kerr effect (MOKE) and magnetic dichroism (XMCD), I showed the uniaxial in-plane anisotropy of the films, exhibiting a compensation wall at the ad-hoc composition. I investigated the thermal evolution of the magnetization of the Co and Gd sub lattices, accounted by simulations performed from a mean field model. Ultrathin Pt/Co(5Å)/Pt films display an easy axis for magnetization anisotropy perpendicular to layer surface. When this anisotropy and the dipolar one, which drives the magnetization towards the plane, are of the same order of magnitude, a transition from perpendicular to planar anisotropy, so called spin reorientation transition (SRT), occurs. During my PhD, I studied the mechanism underlying such reorientation of magnetization and the slow fluctuations regime associated, whereas the anisotropy is finely tuned by ion irradiation
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Bui, Lynn. "10/60: Make Gravity Visible : A social movement to challenge our society to move more." Thesis, Umeå universitet, Institutionen Designhögskolan, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-74463.
Full textAbstract:
Gravity plays a vital role in our everyday lives. It provides the development of our muscle mass which fuels our brain’s advancement and our ability to complete daily tasks. Yet we often take for granted the things we do not see. From hunting and gathering, chasing after prey, migrating from one place to the next, to growing and harvesting crops to long hours laboring away, we have felt gravity through millions of years in time. Along with the rise of technology, we are witnessing the fall of our physical selves. Our lives have become busier, more stressful and our days behind a screen much longer. Within the past 30 years, gravity has been intercepted by the chair and the ratio of moving to sitting has been reversed. Instead of feeling this force within our legs and lower limbs, it has now been deferred to our fingers, buttocks and backs. We spend the bulk of our days in a seated position, often behind a screen. Sitting has become such a norm that daily exercise at the gym is no longer enough to offset all the negative things done to our bodies in a sedentary posture. We were programmed to move, but we’ve hacked our brains to think otherwise. Prolonged sitting is a serious issue that should not be overlooked. The challenge is to change a habit that we’ve acquired from an early age. The numbers are staggering, over 1.5 billion people worldwide are obese.(WHO. int, 2013) 5.3 million die each year from heart related diseases and diabetes as indirect result of the chair, .3 million more than smoking. (Thelancet.com, 2012) It is time to break the norm, adjust our perceptions, expectations and stop living in extremes and move towards moderation. It’s time to stand up and make gravity visible. 10/60: Make Gravity Visible is a social movement to challenge our society to move more, reminding people to be up and moving 10 minutes for every 60 minutes. The goal is to challenge society to integrate movement within the home, work and societal environments through the support and influence of communal behaviour. 10/60 is facilitated by a website and a smartphone application. The website provides ideas shared by the community to help inspire movement into people’s lives. The app tracks a person’s daily physical activity levels and sends a reminder when he/she has been sitting for too long. How much a person moves is reflected by an avatar’s physical state as well as graphical data by the time of day. Challenges can be submitted within the inner circle of friends to encourage more movement. The initial strategy around this topic was through the intersections of four subjects: human evolution, philosophy, behavioral psychology, and physiology. This concept was developed based on findings from foundational research, expert interviews, user tests, experiments and behavioral observations - in particular social influences and the underlying principle that motivation is different for everyone. Awareness alone does not generate action. Motivating people to move more is beyond an individual problem - sitting is a societal and cultural issue and unless that is addressed, no long term changes can be sustained. This project aims to inspire people to leverage their communities and integrate more physical activity in the home, work and societal environments. Societal and cultural norms will not change unless we change together.
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Zhao, Can. "Mode-of-action of PAF26 and the discovery of more active and stable cyclic PAF26 derivatives." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/23637.
Full textAbstract:
The significance of fungal infections has been grossly underestimated. Only a few drugs are clinically available to treat life-threatening fungal infections, and resistance against these drugs is rising. Antifungal peptides (AFPs) are being actively explored as novel pharmaceuticals. PAF26 is a de novo designed hexapeptide possessing N-terminal cationic and C-terminal hydrophobic regions. Previously the roles of each of these motifs in the antifungal mode-of-action of PAF26 have indicated that it involves three stages: interaction with the plasma membrane, internalisation, and cell killing. The overall aim of my project was to obtain further insights into its mode-of-action and develop more active antifungal derivatives of PAF26. Three experimental fungal systems were used in this study: the model Neurospora crassa, the human pathogen Aspergillus fumigatus and the plant/human pathogen Fusarium oxysporum. The first objective of the study was to evaluate the impact of different fluorescent labels on the intracellular localisation and antifungal properties of PAF26. For this purpose a library of PAF26 labelled with 13 different fluorophores was synthesised. This library contained PAF26 conjugates of broad chemical and spectral diversity. These fluorescent PAF26 conjugates were analysed by live-cell imaging and tested for their antifungal activities. The different fluorescent labels were found to have significant impacts both on intracellular localisation and antifungal activities. TMR, carboxyfluorescein, NBD and DMN were found to be the best labels for live-cell imaging because they had the least influence on the intracellular localisation and antifungal activity of PAF26. The second objective was to identify target proteins of PAF26 in N. crassa cells. A large number of proteins were identified as binding to PAF26 from a protein pull-down and mass spectroscopy analysis using TMR- and fluorescein-labelled PAF26. One of these proteins was the highly abundant plasma membrane ATPase PMA-1. An in-silico analysis showed that PMA-1 is likely to be a major target protein of PAF26. The final objective was to develop novel antifungals based on PAF26 with improved activities and stability. Novel cyclic derivatives of PAF26 were designed in-silico against PMA-1. These peptides were synthesised and tested against N. crassa, A. fumigatus and F. oxysporum and were found to have higher activities (at the sub-micromolar level) and greater stability than the linear PAF26. Overall this study has provided novel mechanistic insights into the mode-of-action of PAF26 and discovered novel highly active antifungal peptides with clinical potential as therapeutics.
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Bowles, Angela. "Student Engagement and Satisfaction in the move to Blended and Online Mode Learning in Higher Education." Thesis, Griffith University, 2021. http://hdl.handle.net/10072/409171.
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This study sought to advance understanding of student perceptions around their engagement in the move towards blended and online mode learning in higher education. Therefore, the research aimed to explore the extent to which different demographic groups of students have engaged in blended and online methods within a cross-section of courses within a higher education context. More specifically, the study endeavored to investigate specific student preferences around the move from traditional face-to-face to more blended and online learning environments. Furthermore, the research aimed to gather student perceptions of internet use in their learning to consider how to more effectively use blended and online modes to aid in student transition and engagement whilst driving satisfaction.
The project adopted a mixed method design of both quantitative and qualitative research to explore the extent to which students feel engaged and satisfied when adopting blended and online learning techniques within a variety of courses in the business school of a large Australian university. Initially, study 1 focused on a quantitative approach collecting data from a mix of 767 undergraduate students segmented across different groups. The main established scale items proposed were adapted from Krause and Coates (2008) around key areas of student transition, academic, peer, student-staff, intellectual, online and beyond class engagement. The results from the surveys aimed to suggest that student levels of engagement and satisfaction differ across the use of traditional face to face versus blended and online modes. Findings from this research looked to identify that despite the high daily use of internet among students this is not necessarily their first preference for learning as they value traditional modes.
Additionally, study 2 used semi-structured interviews conducted with 50 full-time and part-time students from across various years within their degrees in a randomly selected sample that self-nominated from study 1. The research highlighted that students are influenced by the ability to interact with their lecturers and tutors as well as their peers to gain the necessary support they feel impact on their success. The outcomes of the study acknowledged that students value the ability to ask questions, be involved in group work as well as the wider university community, whilst also being able to access learning online. Despite these preferences that propose that students still value face to face mode, the interview results also suggested that students value the convenience, accessibility, and flexibility of blended and online modes. However, it was evident that institutions need to offer a variety of mode preferences to suit the mix of students needs in the current higher education market.
Ultimately, the study looked to consider student preferences towards the move to more blended and online learning in higher education. Whilst having explored the interplay among students, academics and the university to determine student learning transformation in different modes. Consequently, the purpose of the project was to gain a better understanding of the key strategy’s universities can adopt to manage their students more effectively and drive engagement in a blended mode, mixing face-to-face and online learning environments. This research has both theoretical and practical implications by informing institutions of student preferences around adopting blended and online modes in order create better practice, which remain under-researched in the marketing and business education literature. Subsequently, the discussion in this study endeavoured to investigate student learning preferences around the move to blended and online learning in higher education and the impact their overall engagement and satisfaction.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Dept of Marketing
Griffith Business School
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Шабельник, Юрій Михайлович, Юрий Михайлович Шабельник, and Yurii Mykhailovych Shabelnyk. "Фізичні властивості плівкових гранульованих сплавів на основі магнітних і благородних металів." Thesis, Вид-во СумДУ, 2014. http://essuir.sumdu.edu.ua/handle/123456789/38926.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата фізико-
математичних наук за спеціальністю 01.04.07 – фізика твердого тіла. –
Сумський державний університет, Суми, 2015.
Дисертацію присвячено комплексному дослідженню структурно-фазового
стану, електрофізичних та магніторезистивних властивостей плівкових
гранульованих сплавів і твердих розчинів на основі Co або Fe та Ag або Au. У
роботі визначені оптимальні умови формування плівкових сплавів і досліджені
процеси фазоутворення в них під час відпалювання.
Удосконалена методика отримання плівкових зразків методом
пошарової конденсації з подальшою термообробкою до температури
відпалювання 700–900 К.
Досліджені тензорезистивні властивості т. р. з елементами гранульованого
стану плівок, осаджених на металеві підкладки.
Визначені оптимальні загальні концентрації магнітних компонент
(с = 40–60 ат. %) у плівкових зразках, що забезпечують утворення термічно
стабільних, із максимальною величиною магнітоопору т. р. з можливим
утворенням гранульованого стану Со або Fe. Максимальні значення МО
спостерігаються в термовідпалених до Тв = 900 К зразках при поперечній
геометрії на основі Со та Ag (Co(5)/Ag(20)/Co(5)/П – МО = 1,5–1,8 %,
сСо = 58 ат. %), а при сСо = 70 ат. % МО = 0,4–0,5 %. Цей факт можна пояснити
додатковими процесами розсіювання електронів провідності на межах гранул.
Установлена кореляція між структурно-фазовим станом та термо-, тензо- і
магніторезистивними властивостями плівкових гранульованих сплавів.
Запропонована та апробована теоретична напівфеноменологічна модель
КТ для плівкових гранульованих сплавів.Диссертация на соискание ученой степени кандидата физико- математических наук по специальности 01.04.07 – физика твердого тела. – Сумский государственный университет, Сумы, 2015. Диссертация посвящена комплексному исследованию структурно- фазового состояния, электрофизических и магниторезистивных свойств пленочных гранулированных сплавов и твердых растворов на основе Co или Fe и Ag или Au. В работе определены оптимальные условия формирования пленочных сплавов. Кроме того, исследованы процессы фазообразования в образцах при термоотжиге. Усовершенствованная методика получения пленочных образцов методом послойной конденсации с последующей термообработкой до температуры отжига 700–900 К дала возможность получать термичностабильные структуры. Так, образцы, полученные одновременной конденсацией, были температурно нестабильны, что проявлялось при отжиге увеличением кристаллитов т. р. и, соответственно, уменьшением величины магнитосопротивления. Исследованы тензорезистивные свойства пленочных образцов, осажденных на металлические подложки, в которых при термоотжиге формируется т. р. с элементами гранулированного состояния. Для этого были использованы металлические подложки с нанесенным специальным шаром диэлектрика «полиимид». В таких образцах наблюдается рост коэффициента тензочувствительности (КТ) примерно в 2 раза относительно однослойной пленки металла. Увеличение КТ можно объяснить образованием в структуре образца гранул Co или Fe. На зависимостях lм от l для пленочной системы Ag(45)/Co(36)/П наблюдается эффект аномального увеличения коэффициента тензочувствительности от деформации. Максимум на зависимости мгновенного КТ соответствует границе перехода упругая / пластическая деформация. Определены оптимальные общие концентрации магнитных компонент (с = 40–60 ат. %) в пленочных образцах, обеспечивающих образование термически стабильных, с максимальной величиной магнитосопротивления (МС) т. р. с возможным образованием гранулированного состояния Со или Fe. Так, максимальные значения МС наблюдаются в термоотоженных до Тот = 900 К образцах при поперечной геометрии на основе Со и Ag (Co(5)/Ag(20)/Co(5)/П – МС = 1,5–1,8 %, сСо = 58 ат. %), а при сСо = 70 ат. % МС = 0,4–0,5 %. Данный факт можно объяснить дополнительными процессами рассеяния электронов проводимости на границе гранул. Таким образом, интерфейсное рассеяние способствует увеличению величины МС. Максимальное значение SB будет наблюдаться в пленочных образцах с максимальным значением МО и минимальным значением поля насыщения. Если говорить о температуре отжига, то при 700 и 900 К чувствительность имеет минимальное значение и существенно возрастает (в 2–3 раза) при Тот = 800 К. Установлена корреляция между структурно-фазовым состоянием, термо-, тензо- и магниторезистивными свойствами пленочных гранулированных сплавов. Определено, что для пленочных структур, в которых при термоотжиге образовался т. р. наблюдается рост ТКС, КТ и МС. Предложена и апробирована теоретическая полуфеноменологическая модель КТ для пленочных гранулированных сплавов. Результаты, рассчитанные по теоретической модели для ТКС с точностью до 12 %, согласуются с экспериментальными.
Thesis for a Doctor of Philosophy degree (Ph. D.) in Physics and Mathematics on speciality 01.04.07 – Solid State Physics. – Sumy State University, Sumy, 2015. The thesis is devoted to comprehensive investigation of phase structural state, electrophysical and magnetoresistive properties of granular alloys and solid solution based on Co or Fe and Ag or Au. This paper contains the study of optimal conditions for formation of the granular alloys that provide the least imperfection of the samples. Phase formation processes in such systems during annealing were investigated. Method for obtaining of the film samples by condensation with subsequent heat treatment to 700–900 K temperature annealing is improved. Tensoresistive properties of the s.s. with elements of the granular state deposited on metallic substrates are investigation. Optimal general concentration of the magnetic components (с = 40–60 at. %) in thin samples that provide thermally stable and the greatest value of magnetoresistance of the s.s. with the possible formation of the granular state of Co or Fe are determined. The correlation between phase structural, thermo-, tenso- and magnetoresistance properties of granular alloys based on Co or Fe and Ag or Au was found. Theoretical semiphenomenological model of strong coefficient of the granular alloys are proposed and tested.