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1
Roos, Andreas. "Growth and characterization of advanced layered thin film structures : Amorphous SmCo thin film alloys." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-177674.
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This report describes the growth and characterization of thin amorphous samarium-cobalt alloy films. The samarium-cobalt alloy was grown by DC magnetron sputtering in the presence of an external magnetic field parallel to the thin film. The external magnetic field induces a uniaxial in-plane magnetic anisotropy in the samarium-cobalt alloy. The thin films were characterized with x-ray scattering, and the magnetic anisotropy was characterized with the magneto optic Kerr effect. The measurements showed a uniaxial in-plane magnetic anisotropy in the samarium-cobalt alloy films. It is not clear how amorphous the samples really are, but there are indications of crystalline and amorphous areas in the alloys.
2
ROMERO, SERGIO A. "Producao e caracterizacao de filmes finos de SmCo." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10915.
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3
Subba, Rao Karavadi. "Microstructure and Texture of Yttrium-Nickel-Borocarbide and Samarium-Cobalt Thin Films." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1153317232040-33715.
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The goal of this thesis is to study the microstrucutre and texture of Yttrium-Nickel- Borocarbide and Samarium-Cobalt thin film heterostructures prepared by Pulsed Laser Deposition and to establish structure-property relations for these materials in order to improve their properties and design new structures. Coincidence site lattice epitaxy was explored in most of these heterostructures (substrate, buffer and film) and studied in detail for each case. Epitaxial thin films of the superconducting borocarbide compound YNi2B2C were grown on single crystal MgO (100) substrates without and with Y2O3 buffer layer using pulsed laser deposition (PLD). In both cases YNi2B2C grows with [001] normal to the substrate. However, the in-plane texture depends on the starting condition. For samples without buffer layer, oxygen from the substrate diffuses into the film and forms an Y2O3 reaction layer at the interface. As a consequence, a deficiency of Y is generated giving rise to the formation of secondary phases. On the other hand, using an artificial Y2O3 buffer layer secondary phases are suppressed. The texture of the Y2O3 layers determines the texture of the YNi2B2C film. The superconducting properties of the borocarbide films are discussed with respect to texture and phase purity. To prevent the formation of an impurity phase at the interface, it was the aim of this preliminary investigation to study YNi2B2C films deposited onto single crystal MgO (100) substrates with an Ir buffer layer. The Ir buffer layer shows a strong cube-on-cube texture onto MgO(100) and also prevents the formation of an Y2O3 interlayer. However, during deposition of YNi2B2C the buffer layer disappears by Ir diffusion into the borocarbide film. The YNi2B2C film exhibits a c-axis texture consisting of four components. As a consequence of these effects, the superconducting transition Tc90 equals up to 13K, but with a transition width of 4K. In the second part of this work, hard magnetic Sm-Co/Cr films were epitaxially grown on MgO(100) and (110) substrates. They were characterized by X-ray pole figure measurements and transmission electron microscopy. For films deposited on MgO(100) at 700ºC, orientations are found with the c-axis aligned in-plane and out-of-plane. By lowering the deposition temperature to 370ºC, the out-of-plane orientations disappeared. Further lowering to 350ºC leads to the formation of amorphous regions in the SmCo5 film. For films grown on MgO(110) the Cr buffer deposition temperature plays an important role. When deposited at 700°C Cr(211) and (100) growth is observed leading to two different types of SmCo5 in-plane orientations. By lowering the Cr-buffer deposition temperature to 300ºC only one buffer and one SmCo5 orientation exists: Cr(-211)[0-11] and SmCo5(10-10)[0001]. The exact orientation relationships between substrate, buffer and films are explained and their correlation with magnetic properties are discussed.
4
Oates, Colin John. "Magnetic studies of cobalt based granular thin films." Thesis, University of St Andrews, 2002. http://hdl.handle.net/10023/12928.
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The magnetic recording media used for hard disks in laptops and PC's is constantly being improved, leading to rapid increases in data rate and storage density. However, by the year 2010, it is predicted that the superparamagnetic limit will be reached, which is potentially insufficient for data storage. At the beginning of this century, CoCr -based alloys are used in longitudinal media since cobalt has a high magnetocrystalline anisotropy. In this thesis, the static and dynamic properties of longitudinal recording thin films were investigated in order to explain and correlate their magnetic characteristics to their recording properties. The samples in question were test samples and some were in commercial use. Magnetic techniques such as high field ferromagnetic resonance and torque magnetometry were used to determine accurately the crystalline anisotropy field. High field ferromagnetic resonance is an ideal tool to determine the crystalline anisotropy, magnetisation, Lande g-factor and the gyromagnetic damping factor. In contrast to previous work, there are no FMR simulations and so all the relevant parameters were determined directly from measurement. Ideally, there should be no exchange interactions between the neighbouring cobalt grains; however, interactions between the grains within the CoCr-alloy recording layer exist. Previous work on the measurements of interactions in recording media involves measuring the sample's magnetisation. In this thesis, an alternative novel method involves torque magnetometry. Another technique that was used in this thesis is small angle neutron scattering, which aims to determine the size of the magnetic grains and compare that with the physical size determined from TEM, by Seagate. There is an extended section on CoxAg1-x granular thin films, which involves determining the sample's g-factor, effective anisotropy, grain size, exchange constant and comparing the FMR lineshapes at 9.5 and 92GHz.
5
Wiedmann, Michael Helmut. "Magnetic and structural properties of ultra-thin cobalt films." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186876.
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In situ polar Kerr effect measurements have been used to study the magnetic anisotropy of Au(111)/Co/X, Pd(111)/Co/X, Cu(111)/Co/X, and Pd(100)/Co/X sandwiches, where X is the nonmagnetic metal Ag, Au, Cu, Ir, and Pd or the insulator MgO. The films were grown by molecular beam epitaxy (MBE). For the metals, we found that the magnitude of the Co/X perpendicular interface anisotropy is strongly peaked at ∼1 atomic layer (1.5-2.5 Å) coverage. To investigate structural influences on the anisotropy, we have used reflection high energy diffraction (RHEED) and low energy electron diffraction (LEED) to measure changes resulting from overlayer coverage. Analysis of digitized RHEED images captured every ∼1 Å during metal overlayer coverage shows no abrupt change of the in-plane lattice constant. We have also investigated the out-of-plane lattice spacing as a function of nonmagnetic metal coverage by measuring LEED I-V curves along the (0,0) rod. In the case of Cu, where the LEED behavior is nearly kinematic, we see no evidence of any abrupt structural changes at ∼1 atomic layer coverage. These results suggest the observed peak in magnetic anisotropy is not structural in origin. The influence of an insulating overlayer, MgO, on the perpendicular magnetic properties was also investigated.
6
Joyce, David Edward. "The structure of cobalt based multilayer thin films." Thesis, University of Salford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300769.
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Van, Leeuwen Robert Alan. "Structural and magnetic properties of cobalt/palladium superlattices, ultra-thin cobalt films and manganese antimony alloys." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186431.
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Structural, magnetic, and magneto-optical properties of Co/Pd and Co/Pd/Cu superlattices, ultra-thin Co films and MnSb alloys have been studied. The superlattices and Co films were grown by molecular beam epitaxy (MBE) while the MnSb alloy films were made by sputtering techniques. Several x-ray diffraction techniques were used to analyze the physical structure of the superlattices and alloys. Magnetometry techniques were used to determine some of the room temperature and temperature dependent magnetic properties of the films. In situ and ex situ measurements of the magneto-optical properties of the ultra-thin Co films and alloys also were made.
8
Gana, Usman Muhammadu. "A magnetic and structural study of CoCr-Pt,Ta alloy thin films." Thesis, University of Salford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281613.
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Taylor, Anthony Park 1963. "Terbium iron cobalt diffusion barrier studies." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276931.
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Thin films (5nm ± 2nm thick) of ZrO2, Al2O3, TiO2, Sm, Gd, Zr, Ni, and Pt were deposited onto TbFeCo films (100nm ± 20nm thick) on silicon and graphite substrates and analyzed with XPS as prospective candidates for TbFeCo diffusion barriers. Metals were chosen primarily according to electronegativity. Samples were typically heated to 272°C in UHV for 20 hours to enhance diffusion. Experiments with the metals were performed in a more consistent manner than with the oxides. The Sm, Gd, and Zr were reactively oxidized during the deposition. The Sm/Sm-oxide and Gd/Gd-oxide appeared to be favorable candidates for TbFeCo diffusion barriers. TbFeCo was not detected near the surface before or after heating the samples to 272°C for 20 hours and depth profiles indicated oxygen contamination decreased steadily as the barrier/TbFeCo interface was approached. For the other materials examined, either the oxides were reduced (at least partially) during heating to 272°C (381°C for Al₂O₃) or diffusion of TbFeCo was detected after heating, indicating that they would not be favorable candidates for TbFeCo diffusion barriers.
10
Amiri-Hezaveh, A. "Photelectron spectroscopy of ultra-thin epitaxial f.c.c. magnetic films of iron and cobalt." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233668.
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Deng, Yuanyuan, and 邓远源. "Magnetic circular dichroism and Hall measurement of cobalt-doped zinc oxide thin films." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B50434494.
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The observation of ferromagnetism of (Ga,Mn)As by Ohno in 1998 has inspired great interest in diluted magnetic semiconductors (DMS). DMS’s features combining ferromagnetism and semiconducting make them of great potential for conceptual spintronic devices, which is a promising field of research for the emerging electronics. The practical application of DMS requires a Curie temperature well above room temperature and an intrinsic ferromagnetism. There are several types of DMS materials. The typical ones are transition-metal (TM) doped GaAs, GaN and ZnO. The TM-doped ZnO has drawn particular attention due to the observation of room temperature ferromagnetism in this system including cobalt-doped ZnO.But the origin of ferromagnetic TM-doped ZnO is still unknown after a decade’s theoretical and experimental effort on this material.
In this thesis, we do the magnetic circular dichroism(MCD) and Hall measurement of high quality Cobalt-doped ZnO thin films grown by molecular beam epitaxy (MBE). Room temperature ferromagnetism is observed in these samples. Combining the data from MCD and Hall measurement, we attribute the room temperature ferromagnetism in this system to the impurity band of the doped Cobalt cations.<br>published_or_final_version<br>Physics<br>Master<br>Master of Philosophy
12
Cooke, Michael D. "Magnetostrictive properties of polycrystalline iron cobalt films." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340249.
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Nallan, Himamshu, Thong Ngo, Agham Posadas, Alexander Demkov, and John Ekerdt. "Area Selective Deposition of Ultrathin Magnetic Cobalt Films via Atomic Layer Deposition." Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-207142.
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The work investigates the selective deposition of cobalt oxide via atomic layer deposition. Methoxysilanes chlorosilane and poly(trimethylsilylstyrene) self-assembled monolayers are utilized to prevent wetting of water and cobalt bis(N-tert butyl, N'-ethylpropionamidinate) from the substrate, thereby controlling nucleation on the substrate and providing a pathway to enable selective deposition of cobalt oxide. Sr and Al are deposited atop the oxide films to scavenge oxygen and yield carbon-free cobalt metal films. Thermal reduction of the oxide layer in the presence of CO and H 2 was also investigated as an alternative. Finally, we demonstrate control over the tunability of the coercivity of the resultant films by controlling the reduction conditions.
14
Yi, Jae-Young. "Microstructure and magnetic properties of Co-(CoO, CoNiO2̳, NiO) and Cox̳Ni1̳-̳x̳-CoO nanocomposite thin films /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p3000403.
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Chioncel, Mariana F. "Cobalt thin films produced by conventional and photo-assisted metal-organic chemical vapour deposition." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327638.
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Sharma, Shalini [Verfasser], Lambert [Akademischer Betreuer] Alff, and Oliver [Akademischer Betreuer] Gutfleisch. "Structural and magnetic properties of epitaxial rare-earth cobalt thin films / Shalini Sharma ; Lambert Alff, Oliver Gutfleisch." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2020. http://d-nb.info/1211726215/34.
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Deacon, Liam Matthew. "Structural, electronic and magnetic studies of polar zinc oxide surfaces and their interfaces with ultra-thin cobalt films." Thesis, University of Reading, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625440.
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Zinc oxide (ZnO) has a desirable combination of opto-electronic properties that, when combined with magnetic transition metal dopants such as cobalt, place it at the forefront of next generation materials to harness both electron charge and spin in the field now known as spintronics. In this thesis the polar (0001) surfaces of ZnO single crystals are revisited and used as a basis for the growth of ultrathin cobalt films before subsequent processing in an effort to produce a CoZnO dilute magnetic semiconductor. A method using Zn sublimation partial pressures is given that provides reliable preparation of clean ZnO(0001) surfaces and comparisons between these two surface terminations are made on the basis of LEED, STM, UPS and XPS arguments.
18
Butterfield, Martin Thomas. "Surface structure of ultrathin metal films deposited on copper single crystals." Thesis, Loughborough University, 2000. https://dspace.lboro.ac.uk/2134/33132.
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Ultrathin films of Cobalt, Iron and Manganese have been thennally evaporated onto an fcc Copper (111) single crystal substrate and investigated using a variety of surface structural teclmiques. The small lattice mismatch between these metals and the Cu (111) substrate make them an ideal candidate for the study of the phenomena of pseudomorphic film growth. This is important for the understanding of the close relationship between film structure and magnetic properties. Growing films with the structure of their substrate rather than their bulk phase may provide an opportunity to grow materials with novel physical and magnetic properties, and hence new technological applications. Both Cobalt and Iron have been found to initially maintain a registry with the fee Cu (111) surface in a manner consistent with pseudomorphic growth. This growth is complicated by island rather than layer-by-layer growth in the initials stages of the film. In both cases a change in the structure of the film seems to occur at a point where the coalescence of islands in the film may be expected to occur. When the film does change structure they do not form a perfect over-layer with the structure of their bulk counterpart. The films do contain a number of features representative of the bulk phase but also contain considerable disorder and possibly remnants of fcc (111) structure. The order present in these films can be greatly improved by annealing. Manganese appears to grow with an fee Mn (111) lattice spacing and there is no sign of a change in structure in films of up to 4.61 ML thick. The gradual deposition and annealing of a film to 300°C, with a total deposition time the same as that for a 1 ML thick film, causes a surface reconstruction to occur that is apparent in a R30° (√3×√3) LEED pattern. This is attributed to the formation of a surface alloy, which is also supported by the local expansion of the Cu lattice in the (111) direction.
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Mackay, Kevin George Hamilton. "Fabrication and characterisation of high moment thin films for inductive write heads." Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314178.
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Mukherjee, Devajyoti. "Growth and Characterization of Epitaxial Thin Films and Multiferroic Heterostructures of Ferromagnetic and Ferroelectric Materials." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3622.
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Multiferroic materials exhibit unique properties such as simultaneous existence of
two or more of coupled ferroic order parameters (ferromagnetism, ferroelectricity,
ferroelasticity or their anti-ferroic counterparts) in a single material. Recent years have
seen a huge research interest in multiferroic materials for their potential application as
high density non-volatile memory devices. However, the scarcity of these materials in
single phase and the weak coupling of their ferroic components have directed the
research towards multiferroic heterostructures. These systems operate by coupling the
magnetic and electric properties of two materials, generally a ferromagnetic material and
a ferroelectric material via strain. In this work, horizontal heterostructures of composite
multiferroic materials were grown and characterized using pulsed laser ablation technique.
Alternate magnetic and ferroelectric layers of cobalt ferrite and lead zirconium titanate,
respectively, were fabricated and the coupling effect was studied by X-ray stress analysis.
It was observed that the interfacial stress played an important role in the coupling effect
between the phases. Doped zinc oxide (ZnO) heterostructures were also studied where
the ferromagnetic phase was a layer of manganese doped ZnO and the ferroelectric phase
was a layer of vanadium doped ZnO. For the first time, a clear evidence of possible room
temperature magneto-elastic coupling was observed in these heterostructures. This work
provides new insight into the stress mediated coupling mechanisms in composite
multiferroics.
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Liakakos, Nikolaos. "Organometallic approach to the growth of metallic magnetic nanoparticles in solution and on substrates." Thesis, Toulouse, INSA, 2013. http://www.theses.fr/2013ISAT0026/document.
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Cette thèse concerne une nouvelle méthode chimique de croissance par germes qui peut produire des assemblés de nanostructures métalliques epitaxiées sur des surfaces macroscopiques cristallines qui agissent comme germes. Cette approche permet d’obtenir des assemblés bien organisées en échelle centimétrique de nanofils métalliques de Co, qui sontmonocristallins, monodisperses de diamètres inferieurs à 10nm et qui ont une orientation perpendiculaire. Ils ont une anisotropie magnétique perpendiculaire et sont intéressantes pour des applications d’enregistrement magnétique à très haute densité. L’extension de cette méthode au fer donne des films nanostructurés de fer. L’orientation des nanostructures sur le support solide dépend de l’orientation cristallographique du substrat, alors que leur morphologie est dictée par la composition de la solution. Cet objectif a été atteint grâce à des études parallèles sur le mécanisme de croissance de nano-cristaux de cobalt en solution qui ont révélées une influence inattendue de la procédure de préparation de la solution mère sur la morphologie des nanocristaux. En plus,l’utilisation des germes nanoscopiques pour la croissance de Co et de Fe a rendu des nanofils longs de Co et des altères de Co-Fe et elle a contribué à la définition et l’amélioration des conditions expérimentales pour la croissance par germes de Co et de Fe sur les substrats solides<br>This thesis concerns a new wet chemical seeded growth method that can produce arrays of metal nanostructures epitaxially grown on crystalline macroscopic surfaces which act as seeds. This approach produces wafer-scale organized 2D hexagonal arrays of perpendicularly oriented, monodisperse and monocrystalline metallic Co nanowires with diameters below 10 nm which exhibit perpendicular magnetic anisotropy and are interesting for applications in ultra high density magnetic recording. Extension of this approach to iron gives rise to nanostructured iron films. The orientation of the nanostructures on the solid substrate depends on the substrate crystallographic orientation, whereas their morphology is dictated by the solution composition. This objective was attained through parallel studies on the growth mechanism of cobalt nano-crystals in solution which revealed an unexpected influence of the stock solution preparation procedure on the nanocrystal morphology. In addition, the use of nanoscopicseeds for the overgrowth of cobalt and iron gave rise to long Co nanowires and Co-Fe dumbbells and contributed to the definition and the improvement of the experimental conditions for the seeded growth of Co and Fe on the solid substrates
22
Rouabhi, Mokhtar. "Mécanismes d'aimantation et dynamique des parois dans des films minces magnétiques amorphes de CoNbZr." Rouen, 1993. http://www.theses.fr/1993ROUES034.
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Dans ce travail, nous avons mené une étude sur la dynamique des mécanismes d'aimantation dans des films minces métalliques magnétiques doux pour tenter une approche différente d'un sujet jusqu'alors réservé aux matériaux isolants massifs. Les couches minces amorphes du composé standard de CoNbZr, que nous avons élaborées par pulvérisation R. F. , sont typiques d'une anisotropie planaire uniaxiale. Nous avons obtenu nos résultats en champs faibles et en champs forts respectivement à l'aide de dispositifs de mesure originaux que nous avons conçus et réalisés : spectre haute fréquence de la perméabilité initiale (jusqu'a 500 MHz) et cycles d'hystérésis (jusqu'à 100 kHz). En champs faibles et pour une direction d'excitation parallèle à l'axe de facile aimantation, nous avons montré que les parois ne contribuent pas aux mécanismes d'aimantation réversibles et qu'elles peuvent être considérées totalement bloquées. Pour expliquer ces observations, nous avons développé une modélisation théorique dans laquelle les parois sont accrochées aux surfaces du film. Ce modèle a été confirmé par nos résultats en champs forts: outre la mise en évidence d'un champ critique de décrochage inversement proportionnel à l'épaisseur du film, nous avons montré que l'ensemble des paramètres des boucles d'hystérésis suivent les lois prévues. D'autre part, la mesure des cycles d'hystérésis à fréquence variable a mis en évidence un net effet de la fréquence dès une centaine de Hz. L'apparition progressive d'effets dissipatifs associés à des courants de Foucault n'exclut pas la contribution éventuelle de phénomènes dissipatifs dus à la relaxation des parois
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Wuchner, Sip Sibylle. "Etude des processus d'aimantation de tri-couches magnétiques à base d'alliages amorphes de terres rares et de cobalt." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10070.
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Nous avons prepare des couches minces amorphes a base d'alliages de terres rares, d'yttrium ou de zirconium et de cobalt par trois types differents de pulverisation cathodique (triode, magnetron toroidal, face-a-face). Les proprietes structurales, chimiques (retrodiffusion de particules chargees, spectrometrie de masses d'ions secondaires, rayons x, microscopie electronique), magnetiques (magnetometre, neutrons), et magneto-optiques (effets kerr) de ces materiaux ont ete caracterises en details. Avec ces materiaux de base, nous avons prepare des tri-couches aux interfaces tres propres permettant d'etudier le couplage magnetique entre couches. Les systemes sandwich fabriques sont typiquement y-co/gd-co/y-co et sm-co/x-co/sm-co' (x=gd, zr, tb). Les trois couches constitutives sont couplees magnetiquement par les interactions d'echange entre moments de cobalt a travers tout l'echantillon. Ce couplage associe aux proprietes specifiques de l'alliage considere (moment magnetique, anisotropie, coercitivite) conduisent a des configurations ferrimagnetiques ou ferromagnetiques de l'aimantation des couches voisines et donnent lieu a des processus d'aimantation originaux. Pour des systemes constitues de couches externes dures de coercitivites differentes et d'une couche centrale douce (sm-co/x-co/sm-co', x=gd, zr), l'influence de l'epaisseur et de la nature du materiau de la couche centrale sur le couplage et les processus d'aimantation ont ete etudies quantitativement. Un etat avec une seule paroi de bloch etendue dans la couche centrale est stabilise. Pour caracteriser cette paroi nous avons effectue des mesures d'aimantation, de reflectometrie de neutrons polarises et des mesures de susceptibilite a haute frequence. Des simulations numeriques a l'aide d'un programme developpe au cours de ce travail pour decrire les processus d'aimantation dans les systemes sandwich rendent particulierement bien compte des courbes d'aimantation experimentales de ces systemes modeles
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SÁ, Luciano Vaz de. "Magnetostricção e Anisotropia Magnética de filmes de Cobalto em substratos de vidro e silício." Universidade Federal de Goiás, 2011. http://repositorio.bc.ufg.br/tede/handle/tde/806.
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Previous issue date: 2011-09-09<br>The Ferromagnetic Resonance technique is used to study the magnetostriction and the magnetic anisotropy of cobalt thin films grown on glass and silicon substrates. The effective values of the magnetostriction and magnetic anisotropy constants obtained do not agree with known values in the literature, but show the viability of the experimental method used [with the film glued to a
cantilever beam under stress] to study the magnetostriction of magnetic thin
films.<br>Este trabalho tem como objetivo estudar a magnetostricção e a
anisotropia magnética de filmes finos de cobalto usando a técnica de Ressonância Ferromagnética. As amostras investigadas foram produzidas pela técnica de magnetron sputtering, depositadas sobre substratos de vidro e silício, com espessuras variando na faixa de 10 a 20 nm. Os valores efetivos obtidos para as constantes de magnetostricção e de anisotropia magnética de
volume e de superfície diferem de valores conhecidos na literatura, mas comprovam a viabilidade do procedimento experimental aplicado [com o filme fixo sobre uma haste cantilever sujeita a stress] para investigar a magnetostricção de filmes finos magnéticos.
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Lenertz, Marc. "Propriétés structurales et magnétiques de cobaltites de types CoV2O6 à structure unidimensionnelle avec un intérêt potentiel pour la spintronique." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-01063444.
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Le but de ce travail de thèse est de réaliser des vannes de spin " naturelles " constituées d'un matériau unique. Le matériau en question doit contenir une alternance de feuillets magnétiques et non magnétiques et présenter différents états magnétiques. Ce système modèle ne présenterait alors ni d'inter diffusion ni de rugosité aux interfaces magnétiques/non-magnétiques et pourrait constituer un système modèle pour les études des phénomènes de transport dépendant de spin. Le CoV2O6 est un oxyde polymorphe de basse dimensionnalité. Les deux phases (α et γ) présentent chacune plusieurs plateaux d'aimantation induits par un champ magnétique. Le premier objectif est de comprendre la structure cristalline et magnétique de ce composé, ce qui a été réalisé par des mesures d'aimantation, de diffraction des rayons X et de neutrons sur des poudres et monocristaux. Les résultats de la phase α sont appuyés par des calculs ab initio. Le second objectif est de déposer ce matériau en couche mince afin d'analyser ses propriétés de transport. Des films épitaxiés de γ CoV2O6 ont été obtenus sur TiO2(100) et TiO2/Pt(111) par ablation laser. Le dépôt sur l'électrode de Pt montre la présence de six variants entrainant l'observation de plateaux d'aimantation supplémentaires.
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Rueff, Jean-Pascal. "Dichroisme circulaire magnétique des rayons X dans les systèmes terre rare - métal de transition : une nouvelle approche pour l'étude des propriétés magnétiques." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10034.
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Le dichroisme circulaire magnetique des rayons x (xmcd) est la difference des sections efficaces d'absorption des materiaux ferro- ou ferrimagnetiques, pour les deux polarisations circulaires de la lumiere. Le xmcd est selectif de l'espece chimique et de l'etat final sonde, par choix du seuil d'absorption. Notre etude porte sur les systemes terre rare - metal de transition, elabores au laboratoire l. Neel. Les poudres la(ni#xco#1#-#x)#5 et tb(ni#xco#1#-#x)#5 et les films amorphes gd-ni-co, ont ete etudies par xmcd, aux seuils l#2#,#3 de la terre rare. Dans ces composes, la variation de l'amplitude du dichroisme avec la teneur en co, peut se decrire dans un unique modele phenomenologique prenant en compte la polarisation de la bande 5d par l'hybridation 3d-5d et la dependance en spin de la partie radiale des elements de matrice dipolaires, due a l'echange 4f-5d. Les signaux geants, observes dans gd-ni-co, resultent de l'anisotropie magnetique, perpendiculaire au plan du film. Le xmcd aux seuils m#4#,#5 des terres rares et l#2#,#3 des metaux de transition, dans les monocristaux de hoco#2 et tbni#5 et dans les films minces amorphes er-fe, a permis l'etude en champ et en temperature du magnetisme 4f et 3d. Dans er-fe, nous avons mis en evidence une transition induite sous champ vers une structure magnetique cantee, prevue dans les modeles theoriques des systemes sperimagnetiques, autour du point de compensation. Les mesures sur les monocristaux ont confirme la sensibilite du dichroisme, detecte en rendement total d'electrons, a l'etat de surface des echantillons. Enfin, les calculs de diffusion multiple, realises au seuil k du co dans les composes r-co, ont montre que le signal de xmcd est correle au couplage spin-orbite dans la bande 5d de la terre rare, via l'hybridation 4p(co)-5d(r)
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Bordel, Catherine. "Etude de la modification par nitruration des propriétés magnétiques des alliages amorphes TbFe et TbFeCo." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10174.
Full textAbstract:
Nous avons elabore par pulverisation cathodique des couches minces amorphes de tbfe et tbfeco nitrurees, dans le but d'etudier le role de l'azote sur les proprietes magnetiques de ces alliages. Des experiences de spectroscopie d'absorption x mettent en evidence l'existence d'un ordre structural local dans les echantillons tbfe(co), que nous considerons comme l'origine de l'anisotropie magnetique perpendiculaire presente dans ces alliages. Les mesures magnetiques macroscopiques montrent une modification tres importante des proprietes magnetiques, notamment une forte reduction de la temperature de compensation et de l'aimantation a saturation de ces materiaux en fonction de leur concentration en azote. L'utilisation de sondes magnetiques chimiquement selectives, telles que le dichroisme circulaire magnetique de rayons x et la spectroscopie mossbauer, permet d'analyser le role de l'azote sur chacun des deux sous-reseaux magnetiques. Ces experiences montrent que l'insertion d'azote provoque essentiellement une modification du sous-reseau de tb, qui consiste en un desalignement croissant des moments magnetiques de tb par rapport a la direction de l'aimantation resultante lorsque la concentration en azote augmente. Un calcul de champ moyen permet de confirmer que ces changements resultent de l'affaiblissement des interactions d'echange tb-fe sous l'effet de la nitruration. Nous avons par ailleurs effectue des experiences de relaxation magnetique qui suggerent que le processus de renversement de l'aimantation de nos alliages tbfe(co) est domine par la propagation de parois de domaines magnetiques. Nous avons enfin complete ce travail par la simulation numerique de courbes d'aimantation a temperature nulle d'un systeme tbfe, qui constitue un premier pas vers l'etude du comportement magnetique de bicouches tbfe-tbfen couplees par echange.
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Vermeulen, Jean-Luc. "Elaboration par pulvérisation ionique et caractérisation de couches minces ferromagnétiques à forte perméabilité." Grenoble 1, 1993. http://www.theses.fr/1993GRE10071.
Full textAbstract:
Dans le cadre des applications employant des materiaux ferromagnetiques aux hyperfrequences, nous avons etudie les proprietes magnetiques et electriques de couches minces ferromagnetiques metalliques et dielectriques deposees par pulverisation ionique. Le premier volet de ce memoire se rapporte a l'installation de depot. Des parametres cles tels que l'orientation de la cible et la temperature du substrat font l'objet d'une analyse approfondie. Cette etude a permis ainsi d'aboutir a l'obtention de couches denses de qualite maitrisee. Sur la base de ces preliminaires, des films minces microcristallises de co-fe-si-b ont ete elabores et caracterises. L'analyse des proprietes magnetiques statiques et dynamiques en fonction des conditions experimentales montre qu'elles sont particulierement sensibles aux deux parametres: temperature de depot et bombardement ionique. Leur controle a permis ainsi de realiser des couches presentant a la fois des permeabilites elevees a basse frequence et de fortes pertes a des frequences plus hautes. En dernier lieu, l'accent est mis sur la realisation et l'etude de couches resistives de b-n et de fe-b-n. Nous montrons qu'il est possible d'obtenir, grace a un bombardement simultane d'ions azote de la couche en croissance, des depots nitrures de concentration en azote variable dans l'intervalle 0-50 pour cent. Concernant les depots de fe-b-n, une forte dependance des caracteristiques electromagnetiques vis-a-vis de la composition a ete observee. Selon la concentration de fer, les proprietes du compose evoluent d'un caractere fortement ferromagnetique et conducteur, a un comportement tres resistif mais a faible induction a saturation
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Balu, R. "Investigations On The Influence Of Process Parameters On The Deposition Of Samarium Cobalt (SmCo) Permanent Magnetic Thin Films For Microsystems Applications." Thesis, 2005. http://hdl.handle.net/2005/1068.
Full textAbstract:
The research in permanent magnet thin films focuses on the search of new materials and methods to increase the prevalent data storage limit. In the recent past the work towards the application of these films to micro systems have also gained momentum. Materials like samarium cobalt with better magnetic properties and temperature stability are considered to be suitable in this regard. The essential requirement in miniaturization of these films is to deposit them on silicon substrates that can alleviate the micro fabrication process. In this work, an effort has been made to deposit SmCo films with better magnetic properties on silicon substrates.
In the deposition of SmCo, the composition of the deposited films and the structural evolution are found to play an important role in determining the magnetic properties. Proper control over these parameters is essential in controlling the magnetic properties of the deposited films. SmCo being a two component material the composition of the films is dependent on the nature of the source and the transport of the material species from source to substrate. On the other hand, structural evolution is dependent on the energetical considerations between the SmCo lattice and substrate lattice. This most often is dominated by the lattice match between the condensing lattice and the substrate lattice. As such Si does not provide good lattice match to SmCo lattice. Hence suitable underlayers are essential in the deposition of these films. Materials like W, Cu, Mo and Cr were used as underlayers. Out of all these Cr is found to provide good lattice match and adhesion to SmCo lattice.
Sputtering being the common deposition tool, SmCo could be sputtered either from the elemental targets of Sm and Co or from the compound target of SmCo5. Sputtering of elemental targets of Sm and Co provides the flexibility of varying the composition whereas sputtering from the SmCo alloy target provides to flexibility of controlling the structural evolution by different process parameters. In this work two different techniques namely Facing Target Sputtering (FTS) and Ion Beam Sputter Deposition (IBSD) were followed in depositing SmCo films.
In FTS technique, SmCo films were directly deposited on silicon substrates by simultaneous sputtering of samarium and cobalt targets facing each other. This sputtering geometry enabled to achieve films with a wide composition range of 55 – 95 at. % of cobalt in single deposition. The resulting composition variation and material property variation were investigated in terms of process parameters like pressure, temperature, SubstrateTarget Distance (STD) and InterTarget Distance (ITD). The composition distribution of the films was found to be dependent on the thermalisation distances and the mean free path available during the transport. To explain the process and the composition variation, a simulation model based on Monte Carlo method has been employed. The simulated composition variation trends were in good agreement with that of the experimental observations.
IBSD, known for its controlled deposition, was employed to deposit both Cr (as an underlayer) and SmCo films. Cr with close epitaxial match with SmCo induces structural evolution in deposited films. The initial growth conditions were found to play a dominant role in the structural evolution of these Cr films. Hence, initial growth conditions were modified by means of oblique incidence and preferential orientation of (200) plane was obtained. With three different angles of incidence, three different surface orientations of Cr films were achieved. These films were then used as structural templates in the deposition of SmCo films. The influence of parameters like composition, impurities, film thickness, beam energy, ion flux, annealing, angles of incidence and underlayer properties on the structural and magnetic properties of SmCo was studied. The structural evolution of SmCo has been found to depend on the structural orientation of Cr underlayers. This followed the structural relation of SmCo(100)||Cr(110)||Si(100) and SmCo(110)||Cr(100)||Si(100). A mixed surface plane orientation was observed in the case of mixed orientation Cr template. The magnetic coercivities were found to increase from 50 Oe to 5000 Oe with the change in the structure of the deposited films.
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Rao, Karavadi Subba [Verfasser]. "Microstructure and texture of yttrium nickel borocarbide and samarium cobalt thin films / by Karavadi Subba Rao." 2006. http://d-nb.info/981353495/34.
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Sharma, Shalini. "Structural and magnetic properties of epitaxial rare-earth cobalt thin films." Phd thesis, 2020. https://tuprints.ulb.tu-darmstadt.de/11812/1/Thesis_ULB_Sharma.pdf.
Full textAbstract:
With the ever increasing demand for beyond-state-of-the magnets, which could also serve in extreme conditions, it is crucial to reduce the dependence on the critical rare-earths and explore new materials or material designs. The cobalt rich compositions of the rare-earth (R) cobalt intermetallic systems offer the combined advantages of a strong magnetocrystalline anisotropy and a high saturation magnetization, well above room temperature. This work focuses on investigating thin films of R-Co intermetallics as model systems for designing the materials at the nanoscale, understanding the magnetic hardness mechanisms and developing more sustainable magnetic systems.
The technique of molecular beam epitaxy (MBE) is utilized to investigate the thin film phase diagrams of lesser critical (Y and Sm), and abundant (Ce) rare-earth cobalt based systems. The growth window of buffer-free (00l) oriented R2Co17 and RCo5 thin films onto (001)-Al2O3 substrate are explored. With the manipulation of individual atomic beams, MBE enables a fine tuning of the stoichiometry, whereby it was possible to stabilize not only the individual phases of Y2Co17 and YCo5 but also a nanocomposite of these phases. The Y2Co17 film has an easy-plane anisotropy matching well to bulk single crystal while the YCo5 film exhibits a perpendicular anisotropy. As a result of exchange coupling of the Y2Co17 phase to the YCo5 phase, the nanocomposite films also shows perpendicular anisotropy. The outcome of a uniaxial anisotropy induced in an easy-plane material of Y2Co17, and hence, the resulting coercivity, shows a potential way of broadening the class of materials useful for permanent magnets.
Furthermore, we were able to fabricate CeCo5 thin films with a saturation magnetization of 500 emu/cm3, a perpendicular anisotropy of 0.44 MJ/m3 and coercivity of 2.74 kOe, which are the highest reported so far for the thin films. An extremely large perpendicular anisotropy of 1.67 MJ/m3 is achieved SmCo5 thin film without the use of any buffer layers. The atomic scale resolution of the film revealed that the SmCo5 phase grows perfectly c-axis oriented on the (001)-Al2O3 substrate, however, with possible traces of the Sm2Co17. The result of a perpendicular anisotropy obtained in single layer of RCo5 phase make them interesting for magnetic recording and spintronic applications.
In view of tuning the magnetocrystalline anisotropy of a compound by strain introduced by chemical substitution, thin films of yttrium substituted cerium (Y,Ce)Co5 intermetallics are investigated. We observed that the structural and magnetic properties of (Y1−xCex)Co5 films show a non-linear dependence on Ce content, x which is supposedly due to a varying chemical valence the Ce ion. The absolute values vary, but a similar trend in the lattice parameters and magnetization is also observed in the bulk single crystals.
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"Preparation and characterization of granular magnetic cobalt silver thin film." 2000. http://library.cuhk.edu.hk/record=b5890295.
Full textAbstract:
by Chiah Man Fat.<br>Thesis submitted in: September 1999.<br>Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.<br>Includes bibliographical references (leaves 94-97).<br>Abstracts in English and Chinese.<br>Acknowledgements --- p.2<br>Abstract --- p.3<br>Table of Contents --- p.5<br>List of Figures --- p.7<br>List of Tables --- p.13<br>Chapter Chapter 1 --- Introduction --- p.14<br>Chapter 1.1. --- Overview --- p.14<br>Chapter 1.2. --- Giant Magnetoresistance (GMR) --- p.15<br>Chapter 1.3. --- Application of GMR Materials --- p.20<br>Chapter 1.4. --- Preparation Methods --- p.22<br>Chapter 1.5. --- This Thesis --- p.23<br>Chapter Chapter 2 --- Sample Preparation and Experimental Methods --- p.24<br>Chapter 2.1. --- MEVVA Ion Source Implanter --- p.24<br>Chapter 2.2. --- The Pulsed Filtered Cathodic Arc Co-deposition System --- p.26<br>Chapter 2.3. --- Sample Preparation --- p.29<br>Chapter 2.3.1 --- Implantation Condition --- p.29<br>Chapter 2.3.2 --- Co-deposition Conditions --- p.31<br>Chapter 2.4. --- Characterization methods --- p.32<br>Chapter 2.4.1 --- Magnetoresistance Measurement --- p.32<br>Chapter 2.4.2 --- Atomic Force Microscopy and Magnetic Force Microscopy --- p.34<br>Chapter 2.4.3 --- Rutherford Backscattering Spectroscopy (RBS) --- p.37<br>Chapter 2.4.4 --- SQUID Magnetometer --- p.38<br>Chapter Chapter 3 --- Characterization of Implanted Samples --- p.39<br>Chapter 3.1. --- Introduction --- p.39<br>Chapter 3.2. --- Results and Discussion --- p.39<br>Chapter 3.2.1 --- Ag Film Thickness Dependence --- p.39<br>Chapter 3.2.2 --- Dose Dependence --- p.44<br>Chapter 3.2.3 --- Extraction Voltage Dependence --- p.46<br>Chapter 3.2.4 --- Annealing Temperature Dependence --- p.49<br>Chapter 3.2.5 --- Thicker Layer Formation --- p.56<br>Chapter 3.2.6 --- AFM and MFM Measurements --- p.58<br>Chapter 3.3. --- Summary --- p.64<br>Chapter Chapter 4 --- Characterization of Co-deposited Samples --- p.65<br>Chapter 4.1. --- Introduction --- p.65<br>Chapter 4.2. --- Results and discussion --- p.65<br>Chapter 4.2.1 --- RBS Measurement --- p.65<br>Chapter 4.2.2 --- Magnetoresistance Measurement --- p.66<br>Chapter 4.2.3 --- AFM Measurement --- p.69<br>Chapter 4.2.4 --- MFM Measurement --- p.76<br>Chapter 4.3. --- Summary --- p.84<br>Chapter Chapter 5 --- Conclusion --- p.85<br>Chapter 5.1. --- Main Results of This Work --- p.85<br>Chapter 5.2. --- Suggestions on Future Works --- p.87<br>Appendix --- p.89<br>Reference --- p.94<br>Publications --- p.97
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Chen, Mei-Ting, and 陳美婷. "Microstructure and Magnetic Properties of Nano Cobalt Thin Films after Ar Ion Beam Bombardment." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/64825330615217380650.
Full textAbstract:
碩士<br>國立中興大學<br>材料科學與工程學系所<br>102<br>In this study, dual ion beam sputtering system is adopted to prepare the Aluminum / Cobalt films on silicon. The microstructure and magnetic properties of the Al/Co films through ion beam bombardment for ten minutes have been studied.
In this experiment, X-ray diffraction analysis is used to confirm the lattice structure; Transmission electron microscopy (TEM) analysis is used to observe microstructure,including grain size, composition and structure and film thickness. The vibrating sample magnetometer (VSM) is used to measure the magnetic properties of thin films.
Results shows that Al / Co films are polycrystalline, Co layer is a hexagonal close-packed (HCP) structure with a lattice constant of a = 4.5 Å, c = 4.11 Å; CoO layer is a FCC structure, lattice constant of a = 4.26 Å; Co3O4 is also a face-centered cubic structure with a lattice constant of a = 8.07 Å. Grain size of the cobalt thin film is estimated to be about 16 ~ 17nm.
The magnetic measurements are made from room temperature (298K) and low temperature (180K),and Al / Co thin film plane is parallel to the applied magnetic field of 12 kOe. The results
Show that is the coercive force at low temperature is about 50 Oe, the exchange bias field is about 5 Oe; room temperature, the coercive force is about 105 Oe, exchange bias field is about 3 Oe. At both the room temperature or 180K , the Al / Co film has no significant coercive force and the exchange bias.
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Chen, Fu-Han, and 陳復漢. "Microstructure and Magnetic Properties of Nano Cobalt Thin Films after Ar/O2 Ion Beam Bombardment." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/p26mq5.
Full textAbstract:
碩士<br>國立中興大學<br>材料科學與工程學系所<br>102<br>The bilayer films of Al/Co on SiO2 substrate was prepared by dual ion-beam deposition technique. The structural and magnetic properties of the films were studied by Grazing Incident X-Ray Diffraction (GIXD), Transmission Electron Microscopy (TEM) and Vibrating Sample Magnetometer (VSM), respectively.
XRD results showed that Co layer consisted of HCP structure with a＝2.50 Å, c＝4.06 Å. Cobalt oxides appeared two compounds：one is CoO layer consisted of FCC structure with a＝4.25 Å and the other is Co3O4 consisted of spinel structure with a＝8.08 Å. TEM results showed that the grain size of polycrystalline films range from 4 to 8 nm and the average is about 6 nm. The thickness of Co and Al film layer is about 50 nm and 13 nm individually, but the AFM cobalt oxides is not obvious by TEM.
Magnetic properties at room temperature (298 K) and field-cooled to 180 K with large applied magnetic field (12 kOe) along the parallel the film surface, both have been measured. Al/CoO/Co film exhibits very tiny exchange bias field (Hex～1.5 Oe) but higher coercivity (Hc～107 Oe) at room temperature (298 K). By field-cooled to 180K, the temperature below the antiferromagnetic Neel temperature (CoO TN～293 K), a slightly increased exchange bias field (Hex~ 2 Oe) and reduced coercivity (Hc～76 Oe) were observed. It may be caused by a invisible AFM layer, internal defects by way of atom diffusion originated from ion beam bombardment.
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"Oxygen Nanodistributions in Cobalt-Iron Electrodeposited Thin Films: Some Effect on Magnetic Properties- High Resolution Analytical Electron Microscopy." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.14893.
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abstract: Soft magnetic alloys play a significant role for magnetic recording applications and highly sensitivity magnetic field sensors. In order to sustain the magnetic areal density growth, development of new synthesis techniques and materials is necessary. In this work, the effect of oxygen incorporation during electrodeposition of CoFe alloys on magnetic properties, magnetoresistance and structural properties has been studied. Understanding the magnetic properties often required knowledge of oxygen distribution and structural properties of the grown films. Transmission electron microscopy (TEM) was a powerful tool in this study to correlate the oxygen-distribution nanostructure to the magnetic properties of deposited films. Off-axis electron holography in TEM was used to measure magnetic domain wall width in the deposited films. Elemental depth profiles of Fe, Co, O were investigated by secondary ion mass spectroscopy (SIMS). Magnetic properties have been determined by superconducting quantum interference device (SQUID) measurements. Oxygen content in the CoFe deposited films was controlled by electrolyte composition. Films were deposited on Si 100 substrates and on other substrates such as Cu and Al. However, a good film quality was achieved on Si substrate. Electron energy loss and x-ray spectroscopies showed that the low oxygen films contained intragranular Fe2+ oxide (FeO) particles and that the high oxygen films contained intergranular Fe3+ (Fe2O3) along grain boundaries. The films with oxide present at the grain boundary had significantly increased coercivity, magnetoresistance and reduced saturation magnetization relative to the lower oxygen content films with intragranular oxide. The differences in magnetic properties between low oxygen and high oxygen concentration films were attributed to stronger mobile domain wall interactions with the grain boundary oxide layers. The very high magnetoresistance values were achieved for magnetic devices with nanocontact dimension < 100 nm and oxide incorporation in this nanoconfined geometry. The content of oxide phase in nanocontact was controlled by concentration of the Fe3+ ions in the electrodeposition solution. Magnetic device integrity was improved by varying amount of additive into plating solution. These results indicated that electrodeposited CoFe nanocontact is a novel class of materials with large application for magnetic field sensors.<br>Dissertation/Thesis<br>Ph.D. Materials Science and Engineering 2012
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Menniti, Matteo. "Tailoring the magnetic anisotropy in amorphous FeZr-based thin films on flexible and solid substrates." Thesis, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-369153.
Full textAbstract:
In this thesis the magnetic properties of novel amorphous magnetic materials grown on a flexible substrate of polyethylene naphthalate and a silicon wafer have been analyzed and characterized. The analyzed films are two films of amorphous Cobalt-Iron-Zirconium(Co36Fe53Zr11 & Co37Fe55Zr8) grown on the flexible substrate and two films of amorphous (Fe89Zr11) doped with boron (B). The B is implanted in a lattice of rings with inner diameter of 10 μm and outer diameter of 20 μm and with the distance between the center of the rings of either 50 μm or 25 μm. The composition in the doped region is Fe80Zr10B10. Various magneto-optical Kerr effect(MOKE) magnetometers are used to measure hysteresis loops of the samples and a superconducting quantum interference device (SQUID) is used to find the volume magnetization of the flexible samples. To measure the anisotropy in the flexible films a series of sample holders has been developed to measure various amount of stress using the same sample in magneto-optical magnetometers. The stress induced uniaxial anisotropy is found by measuring hysteresis loops of the flexible samples while bending them with different curvatures. The induced anisotropy is related to the magnetostriction and the magnetostriction constants is estimated for the two flexible samples by assuming values for Young’s modulus and Poisson’s ratio. The estimated values for the magnetostriction constant are found to vary with the amount of Zr and to be in the correct order of magnitude for magnetic films. The implanted B rings with the short distance of 25 μm between the center showed to have some interaction between the rings. This conclusion is drawn after analyzing first order reversal curves of the samples and looking at the domains under a MOKE-microscope. At very low temperatures the (unimplanted) FeZr matrix is ferromagnetic and seem to have an anti-ferromagnetic coupling with the B rings. At room temperature the rings are still ferromagnetic and they couple to each other.
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Rodewald, Jari Michael. "Advancement of growth and characteristics of ultrathin ferrite films." Doctoral thesis, 2021. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-202102124037.
Full textAbstract:
Within this thesis, (ultra)thin NiFe2O4 (NFO) and CoFe2O4 (CFO) films are prepared via reactive
molecular beam epitaxy (RMBE) on MgO(001) and SrTiO3(001) substrates and are characterized
in terms of their structural, electronic, and magnetic properties. In a first step, the structural properties of ultrathin off-stoichiometric NixFe(3-x)O4 films (0<x<1.5) deposited via RMBE on MgO(001) are investigated in
situ during film deposition by means of synchrotron radiation-based x-ray diffraction (XRD) and ex situ after film growth by high energy surface x-ray diffraction (HESXRD). In the second major step of this work, a
more extensive study on the dependence of the cationic ratio in NixFe(3-x)O4 thin films (0<x<2.07)
grown on MgO(001) is conducted. The film surface structure and chemical composition is characterized in situ by low energy electron diffraction (LEED) and laboratory-based soft x-ray photoelectron spectroscopy (XPS), respectively. Film thicknesses are determined via analysis of x-ray reflectivity (XRR) data, while the
film structure is analyzed by XRD measurements. Further, chemical properties and the electronic
structure of the NFO films with focus on the cationic valencies of Ni and Fe cations with varying
x is investigated by means of (angle-resolved) hard x-ray photoelectron spectroscopy [(AR-)HAXPES]. Complementary x-ray absorption spectroscopy (XAS) and x-ray magnetic circular
dichroism (XMCD) investigations are conducted to obtain information on the cationic site
occupancies and on the element-specific magnetic moments. The latter are compared to magnetic
properties characterized via superconducting quantum interference device (SQUID) magnetometry. In a third step, the type of substrate is changed to SrTiO3(001) to investigate the influence of a larger strain applied by the substrate to NFO films with varying thicknesses. Structural characterization at the surfaces and in the films is conducted by means of LEED, XRR, and (grazing incidence) XRD, whereas XPS and HAXPES provide information on the chemical composition and electronic structure in the near-surface region and in deeper subsurface layers, respectively. Magnetic properties are characterized by SQUID magnetometry. In a fourth step, an alternative pathway for the formation of ferrite thin films is demonstrated exemplarily for CoFe2O4 films on SrTiO3(001), which are formed by interdiffusion of Fe3O4/CoO bilayers. The interdiffusion process was monitored via XRR, soft XPS and AR-HAXPES to determine the bilayer/film structure, stoichiometry, and chemical properties. Analysis of complementary XAS measurements provides additional information on the occupancies of Fe and Co cations during interdiffusion. Final SQUID magnetometry measurements are performed to gain information on the
magnetic properties before and after complete interdiffusion. Overall, within this thesis, it was demonstrated that NFO and CFO thin films can be prepared in high structural quality with sharp interfaces and surfaces, which is crucial for the applicability in the fields of spintronics and spincaloritronics.
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Roy, Debangsu. "Exchange Spring Behaviour in Magnetic Oxides." Thesis, 2012. http://hdl.handle.net/2005/3172.
Full textAbstract:
When a permanent magnet is considered for an application, the quantity that quantifies the usability of that material is the magnetic energy product (BH)max. In today’s world, rare earth transition metal permanent magnets like Nd-Fe-B, Sm-Co possesses the maximum magnetic energy product. But still for the industrial application, the ferrite permanent magnets are the primary choice over these rare transition metal magnets. Thus, in the present context, the magnetic energy product of the low cost ferrite system makes it unsuitable for the high magnetic energy application. In this regard, exchange spring magnets which combine the magnetization of the soft phase and coercivity of the hard magnetic phases become important in enhancing the magnetic energy product of the system. In this thesis, the exchange spring behaviour is reported for the first time in hard/soft oxide nanocomposites by microstructural tailoring of hard Barium Ferrite and soft Nickel Zinc Ferrite particles. We have analyzed the magnetization reversal and its correlation with the coercivity mechanism in the Ni0.8Zn0.2Fe2O4/BaFe12O19 exchange spring systems. Using this exchange spring concept, we could enhance the magnetic energy product in Iron Oxide/ Barium Calcium Ferrite nanocomposites compared to the bare hard ferrite by ~13%. The presence of the exchange interaction in this nanocomposite is confirmed by the Henkel plot. Moreover, a detailed Reitveld study, magnetization loop and corresponding variation of the magnetic energy product, Henkel plot analysis and First Order Reversal Curve analysis are performed on nanocomposites of hard Strontium Ferrite and soft Cobalt Ferrite. We have proved the exchange spring behaviour in this composite. In addition, we could successfully tailor the magnetization behaviour of the soft Cobalt Ferrite- hard Strontium Ferrite nanocomposite from non exchange spring behaviour to exchange spring behaviour, by tuning the size of the soft Cobalt Ferrite in the Cobalt Ferrite/Strontium Ferrite nanocomposite. The relative strength of the interaction governing the magnetization process in the composites has been studied using Henkel plot and First Order Reversal Curve method. The FORC method has been utilized to understand the magnetization reversal behaviour as well as the extent of the irreversible magnetization present in both the nanocomposites, having smaller and larger particle size of the Cobalt Ferrite. It has been found that for the all the studied composites, the pinning is the dominant process for magnetization reversal. The detailed structural analysis using thin film XRD, angle dependent magnetic hysteresis and remanent coercivity measurement, coercivity mechanism by micromagnetic analysis and First Order Reversal Curve analysis are performed for thin films of Strontium Ferrite which are grown on c-plane alumina using Pulsed Laser Deposition (PLD) at two different oxygen partial pressures. The magnetic easy directions of both the films lie in the out of plane direction where as the in plane direction corresponds to the magnetic hard direction. Depending on the oxygen partial pressure during deposition, the magnetization reversal changes from S-W type reversal to Kondorsky kind of reversal. Thus, the growth parameter for the Strontium Ferrite single layer which will be used further as a hard layer for realizing oxide exchange spring in oxide multilayer, is optimized. The details of the magnetic and structural properties are analyzed for Nickel Zinc Ferrite thin film grown on (100) MgAl2O4. We have obtained an epitaxial growth of Nickel Zinc Ferrite by tuning the growth parameters of PLD deposition. The ferromagnetic resonance and the angle dependent hysteresis loop suggest that, the magnetic easy direction for the soft Nickel Zinc Ferrite lie in the film plane whereas the out of plane direction is the magnetic hard direction. Using the growth condition of respective Nickel Zinc Ferrite and Strontium Ferrite, we have realized the exchange spring behaviour for the first time in the trilayer structure of SrFe12O19 (20 nm)/Ni0.8Zn0.2Fe2O4(20 nm)/ SrFe12O19 (20 nm) grown on c-plane alumina (Al2O3) using PLD. The FORC distribution for this trilayer structure shows the single switching behaviour, corresponding to the exchange spring behaviour. The reversible ridge measurement shows that the reversible and the irreversible part of the magnetizations are not coupled with each other.