Dissertations / Theses on the topic 'In situ magneto-optic Kerr effect'

A phenomenological theory of magneto-optic Kerr effect (MOKE) is presented to illustrate the connection between the magnetization and the polarization of light reflection in an isotropic medium. An apparatus measuring the MOKE of magnetic medium was designed and constructed. The surface magneto-optic Kerr effect (SMOKE) of a magnetic multilayer is a measurement of the average magnetization of several layers within the penetration depth of the light.
SMOKE measurements on a series of sputtered $ rm Ni sb{80}Co sb{20}15 A$/CU$(t sb{Cu}),$ where $t sb{Cu}$ is the thickness of Cu spacer layer, multilayers confirms that the coupling strength in these multilayers oscillates from antiferromagnetic (AF) coupling to ferromagnetic coupling as a function of Cu spacer layer thickness. Low-angle x-ray diffraction and SMOKE measurements on a series of AF-coupled $ rm (Ni sb{80}Co sb{20}15 A$/Cu20A) $ times$ N multilayers with bilayer numbers N ranging from 8 to 100 shows that cumulative interface roughness increases with increasing N, as do the saturation field and coercivity. This is possibly due to the out-of-plane anisotropy associated with cumulative interface roughness in multilayers.
An AF-coupled $ rm (Ni sb{70}Co sb{30}15 A$/Cu20A) $ times$ 10 was continually annealed up to 400$ sp circ$C in several steps, and the magnetic behaviour of the sample was evaluated as a function of annealing temperatures. $ rm (Ni sb{70}Co sb{30}15 A$/CU20A/Ni$ rm sb{70}Co sb{30} A$/CU20A) $ times$ 5 multilayer was used for investigating the AF coupling between magnetic layers of unequal thicknesses. Finally, an AF-coupled $ rm (Ni sb{70}Co sb{30}15 A$/Cu20A/Ni$ rm sb{70}Co sb{30}15 A$/Cu35A) $ times$ 5 multilayer was sputtered and used to study the magnetization of an AF-coupled multilayer with two different coupling strengthes.

This thesis is divided into three main sections that deal with optical and magnetic thin films properties and their measurements techniques. Principles of the spectroscopic reflectometry and measurements of optical properties are described in the first part. Results of imaging reflectometry are most important. This technique is based on in situ monitoring of optical properties of SiO2 thin films during etching over the area cca 10 × 13 mm2. In next section magnetic properties of thin films and new apparatus built on the Institute of Physical Engineering of BUT are shown. Magnetic properties were observed by longitudinal magneto-optical Kerr effect. The construction of the device is based on a light beam with rectilinear polarization reflected from magnetic material with turned polarization. For investigation of local magnetic properties of microstructures a microscope objective focusing laser beam on the sample is used. The last part of the thesis is aimed on improving of a spin valve structure Co/Cu/NiFe. This work was done within the frame of the Erasmus project in Laboratoire Louis Néel in Grenoble. The goal was to achieve the value of GMR (Giant Magnetoresistance) as high as possible by changing of deposition parameters. This value describes the rate of resistances in different mutual directions of magnetization in trilayers.

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.

For the past 50 years, the magnetic storage industry has been the ultimate provider, covering the ever-expanding needs of digital mass storage. Up to now, scaling to smaller dimensions has been the core approach for achieving higher areal densities in conventional media. However, recent studies have shown that further miniaturisation is physically bound by superparamagnetic effects. Bit patterned media (BPM) is one of the most promising solutions for extending the areal densities beyond 1Tbit/in². The ability to magnetically characterise novel BPM is a key requirement for its future commercialisation. The work presented in this thesis describes the investigation of the Magneto-Optic Kerr Effect (MOKE) and the Anomalous Hall Effect (AHE) techniques, used in the characterisation of BPM samples. These samples were produced as part of this work using a customised subtractive fabrication process. Continuous thin magnetic films with Ptseed(10nm)/[Co(0.4nm)/Pt(1nm)]x15 composition and perpendicular anisotropy, were deposited using electron-beam (e-beam) evaporation, and subsequently patterned into magnetic nano-islands through means of e-beam lithography and Ar⁺ ion milling. In terms of the MOKE technique, a fully customised polar MOKE system has been developed and successfully used to observe the hysteretic behaviour of magnetic nano-island arrays with varying dimensions. An expected reduction in the MOKE signal due to pattering has been observed, as well as an additional signal reduction due to the scattering effect arising from the non-vertical sidewalls of the dome-shaped islands. In the case of islands with improved shape profile, the magnetic reversal of BPM arrays with islands sizes down to 35nm has been successfully detected, demonstrating a sensitivity of approximately 6x10⁻¹³emu for the MOKE system. In terms of the AHE technique, Au Hall crosses were deposited on top of the BPM arrays that had been previously characterised by MOKE, allowing the direct comparison and cross-verification of the results obtained by the two techniques. A revised Hall cross design, where the Hall crosses were generated by direct patterning of the Pt seed layer, has provided a significant improvement in AHE signal. This has allowed the detection of the magnetic reversal of individual sub-50nm magnetic islands, demonstrating a sensitivity of approximately 6.6x10⁻¹⁵emu for the AHE technique. The spatial sensitivity of these Hall cross structures has been experimentally determined, indicating a decrease in sensitivity with increasing distance from the cross centre and with decreasing island diameter. In conclusion, the sensitivity profile of Hall cross structures must be taken into account for the accurate interpretation of BPM characterisation results obtained by the AHE technique. Finally, some suggestions are outlined with regard to the future improvement of the developed characterisation techniques and the further continuation of the work presented in this thesis.

The effect of optical coatings on the longitudinal magneto-optic Kerr effect response from 10 nm thin films of permalloy (Ni84Fe16) has been studied. Enhancement of the magneto-optic Kerr effect signal contrast of a factor 1.76 has been observed for P- polarized incident light on a trilayer configuration of aluminium, magnesium fluoride, and permalloy. A quadrilayer structure where the trilayer is overcoated with zinc sulphide enhances the signal contrast by a factor 4.05 for P-polarized light. The enhancement is also observed for S-polarized light, and is shown to be reproducible using nickel as the magnetic material and gold instead of aluminium.The experimental data are compared to a simplified theoretical model where the electric field components are calculated using a 4 x 4 matrix algorithm. The model is found to be inadequate in predicting the longitudinal magneto-optic Kerr effect response from complex multilayer structures. This is believed to be due to a simplification in the model disregarding the phase factors of the different components reflected off the multilayered samples.

We present the development of a far-field magneto-optical Kerr effect microscope. An inverted optical microscope was constructed to accommodate Kerr imaging and atomic force microscopy. In Kerr microscopy, magnetic structure is investigated by measuring the polarization rotation of light reflected from a sample in the presence of a magnetic field. Atomic force microscopy makes use of a probe which is scanned over a sample surface to map the topography. The design was created virtually in SolidWorks, a three-dimensional computer-aided drafting environment, to ensure compatibility and function of the various components, both commercial and custom-machined, required for the operation of this instrument. The various aspects of the microscope are controlled by custom circuitry and a field programmable gate array data acquisition card at the direction of the control code written in National Instrument LabVIEW. The microscope has proven effective for both Kerr and atomic force microscopy. Kerr images are presented which reveal the bit structure of magneto-optical disks, as are atomic force micrographs of an AFM calibration grid. Also discussed is the future direction of this project, which entails improving the resolution of the instrument beyond the diffraction limit through near-field optical techniques. Preliminary work on fiber probe designs is presented along with probe fabrication work and the system modifications necessary to utilize such probes.

Cette these presente une etude experimentale, par mesure magneto-optique in-situ, des proprietes magnetiques des structures a base de films ferromagnetiques f(co, fe) deposes sur un substrat d'au(111) et recouverts par un metal de couverture m(au, cu ou v). L'etude de la structure cristallographique, par diffraction des electrons rapides sous incidence rasante et par diffraction des rayons x, des films de v deposes sur un substrat de co(0001) a permis d'identifier une structure cubique centree (cc) du v avec un axe de texture 110 perpendiculaire au plan des couches. Nous avons mis en evidence dans l'evolution de la rotation kerr polaire a saturation #k une variation quasi-lineaire en fonction de l'epaisseur de co, avec une contribution independante de t#c#o. Nous avons montre dans ce cas que cette contribution est liee a la formation des interfaces m/co avec m(au, v), de la meme facon que les comportements transitoires de #k aux faibles epaisseurs de couverture m. Par ailleurs nous avons montre que le modele magneto-optique decrit parfaitement les tendances generales des effets magneto-optiques dans nos echantillons. Nous avons observe des oscillations nettes de #k dans les systemes m(au,cu)/co/au(111) en fonction des epaisseurs d'au ou de cu de couverture. Nous avons propose de les expliquer en termes d'interferences quantiques dependant du spin des electrons de conduction dans la couche paramagnetique de couverture. De la meme maniere, le champ coercitif de films de co(0001) recouverts par du cu oscille quand l'epaisseur de cu augmente. Ce comportement est lie a des oscillations de l'anisotropie perpendiculaire de ces echantillons dues aux d'etats de puits quantique. Enfin, nous avons montre que le couplage intercouche dans au/co/au/co/au(111) presente un comportement oscillant clair en fonction de l'epaisseur de la couche de couverture d'or, avec la meme periode (5 pa) que les oscillations du couplage en fonction de l'epaisseur intercalaire. Ce comportement est observe aussi bien dans le cas du couplage ferromagnetique que antiferromagnetique, dependant de l'epaisseur intercalaire d'or.

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.

Ce travail porte sur l’exaltation de l’effet magnéto-optique (MO) Kerr transverse induite par des «résonances extraordinaires» dans un réseau d’or périodique 1D déposé sur un oxyde de grenat magnéto-optique. La structure complète incluant le réseau métallique 1D a été conçue, simulée numériquement, dimensionnée, fabriquée puis caractérisée. Un algorithme de type RCWA (Rigorous Coupled Wave Algorithm) adapté au calcul parallèle a été développé et utilisé d’une part pour l’étude théorique des modes résonants dans les réseaux magnétoplasmoniques et d’autre part pour l’analyse des données de mesures optiques et magnéto-optiques d’ellipsométrie à base de matrices de Mueller. L’impact sur la réflectivité angulo-spectrale du couplage entre les modes Fabry-Pérot des fentes du réseau et les plasmons de surface à l’interface entre l’or et la couche de grenat MO est ainsi étudié, en utilisant les paramètres optiques et magnéto-optiques réels des matériaux. Pour cela, les caractéristiques optiques du substrat en sGGG (grenat de gallium et gadolinium dopé CaMgZr) et du matériau Bi:GIG (grenat de fer et de gadolinium substitué bismuth) sont au préalable déterminés dans la gamme spectrale 0,73 – 6,42 eV (193 nm-1,7 μm) par ellipsométrie à base de matrices de Mueller. Puis de même la dispersion des composantes magnéto-optiques du tenseur diélectrique est obtenue en appliquant un champ magnétique externe dans le plan, en configuration longitudinale ou transverse. Ces données mesurées sont alors utilisées dans les simulations. Il est ainsi démontré numériquement que grâce à l’interaction des résonances de surface et de cavité dans le réseau 1D l’effet Kerr transverse peut être exalté, éteint ou même de signe inversé, et cela sans renverser ou modifier l’aimantation de la couche magnéto-optique. Pour confirmer les résultats théoriques, une série d’échantillons comportant des réseaux de fentes différentes a été fabriquée par lithographie électronique et procédé de lift-off. Afin de reproduire les données des matrices de Mueller mesurées, les modèles ont été adaptés et optimisés pour tenir compte des imperfections des structures réelles. Les mesures expérimentales confirment l’exaltation de l’effet Kerr magnéto-optique transverse due aux effets magnéto-plasmoniques et prouvent la validité des modèles
This work studies the enhancement of the transverse magneto-optical Kerr effect by exploiting extraordinary resonances occurring in 1D periodic grating. The 1D periodic gold grating structure was designed, described, numerically simulated, and fabricated. A rigorous Coupled Wave Algorithm (RCWA) developed for parallel computing is used for the theoretical study of resonant modes in magnetoplasmonic gratings and for analysis of optical and magneto-optical data measured by Mueller matrix ellipsometry. The impact of coupling between Fabry-Perot modes inside grating air-gaps and surface plasmon mode at the interface between gold and MO garnet layer is studied via spectra of specular reflectivity and for the various angles of incidence. In a first step, the optical functions of the (CaMgZr)-doped gallium-gadolinium garnet (sGGG) substrate and the Bi-substituted gadolinium iron garnet (Bi:GIG) are obtained in the spectral range from 0.73 eV to 6.42 eV (wavelength range 193 nm – 1.7 μm). Subsequently, the spectra of the magneto-optical tensor components are obtained by applying an external in-plane magnetic field in longitudinal and transverse geometry. The obtained functions are then used for numerical simulations demonstrating that by hybridization of surface and cavity resonances in this 1D plasmonic grating, the transverse Kerr effect can be further enhanced, extinguished or even switched in sign and that without inverting or modifying the film's magnetization. To confirm theoretical results a set of samples, gratings with a different width of an air-gap, was fabricated using electron beam lithography and liftoff technique. To be able to reproduce Mueller matrix data from the samples, the models describing realistic structures were further developed and optimized. Experimental measurements of real structures confirm transverse MO effect enhancement using magnetoplasmonic effects and prove applicability of numerical models

Les dispositifs photoniques magnéto-optiques (MO) sont l’objet d’une attention particulière pour leur capacité à améliorer la sensibilité des biocapteurs ou leur sensibilité au champ magnétique. Les effets MO, pouvant se manifester par une rotation de polarisation ou une modification d'intensité de la lumière sous champ magnétique, sont cependant plutôt faibles lors d’interactions simples (réflexion ou transmission) avec les films magnétiques classiques. Le dispositif proposé dans le cadre de ce travail permet d’exalter les effets MO. C’est une structure diélectrique planaire simple formée par un réseau 1D de résine photosensible (PR) déposé à la surface d’un film MO lui-même déposé sur un substrat de verre. Selon les conditions de couplage imposées par le réseau, des modes guidés (TE et TM) sont excités dans le film MO par la lumière incidente, augmentant ainsi l'interaction lumière-matière. Un tel couplage produit ainsi une résonance étroite qui se traduit par un creux (pic) dans le spectre de la transmittance (réflectance). Le film MO est un composite formé par des nanoparticules magnétiques (CoFe2 04) insérés dans une matrice de silice par un procédé sol-gel. Ce composite nano-structurable peut être facilement déposé sur des substrats classiques à faible température de recuit (90°C), ce qui n'est pas le cas de la plupart des matériaux MO utilisés dans les plates-formes d’optiques intégrées. Des exaltations importantes des différents effets de rotation de polarisation (Faraday et Kerr longitudinal) ont été atteintes par les mesures et les simulations grâce à cette structure résonnante toute diélectrique. Les principaux résultats de ce travail concernent cependant l'effet Kerr MO transverse (TMOKE). Cet effet induit un décalage spectral non réciproque de la résonance de transmittance (réflectance) lors de l'inversion de l'aimantation, résultant en une modulation d'intensité. Des valeurs de TMOKE atteignant 9,5% et 18,5% ont été mesurées respectivement en transmission avec T = 80%, et en réflexion avec R = 5%. Ces valeurs très significatives de TMOKE sont principalement dues au facteur de qualité élevé des résonances de transmittance (réflectance) du mode TM. La valeur de TMOKE pour un film MO sans réseau étant d'environ 0,01%, une exaltation de trois ordres de grandeur a ainsi été obtenue grâce à la structure fabriquée. Les valeurs mesurées de TMOKE sont bien positionnées par rapport à la littérature où, à notre connaissance, des valeurs maximales de 1,5% et 15% ont été démontrées expérimentalement par des structures respectivement diélectriques et magnéto-plasmoniques. De plus, des effets magnétiques réciproques inattendus ont été démontrés expérimentalement. Enfin, la structure proposée est un dispositif à faible coût, qui peut être fabriqué sur des substrats à grande échelle, est capable d'exalter tous les effets MO. Cela en fait une structure à fort potentiel pour des applications comme le contrôle non destructif, les capteurs de champ magnétique et même les biocapteurs
Magneto-optical (MO) photonic devices are currently highly desirable because of their ability to improve the sensitivity of biosensors or their sensitivity to the magnetic field. However, MO effects being rather small through classical magnetic films, it is relevant to find ways to enhance such effects which can manifest as light polarization rotation or intensity modification under magnetic field. The proposed device in this work to enhance MO effects is an all-dielectric planar structure formed by a 1D photoresist (PR) grating deposited on top of a MO film itself deposited on a glass substrate. Under coupling conditions through the grating, guided-modes (TE and TM) with narrow resonances are excited in the MO film by the incident light, increasing hence the light-matter interaction. Such coupling results as a dip (peak) in the transmittance (reflectance) spectrum. The MO film is a composite formed by magnetic nanoparticles (CoFe2 04) embedded in a silica matrix and obtained through sol-gel process. This nano-structurable composite can be easily deposited on common substrates with low annealing temperature (90°C), which is not the case of the most MO materials used within integrated optics platforms. Large enhancements of the different non-reciprocal polarization rotation effects (such as Faraday and longitudinal MO Kerr) were achieved experimentally and numerically through the all-dielectric resonant structure. The main results of this work concern the transverse MO Kerr effect (TMOKE). This effect induces a non-reciprocal spectral shift of the transmittance (reflectance) resonance upon magnetization reversal, resulting in an intensity modulation effect. TMOKE values up to 9.5% and 18.5% were measured respectively in transmission with T = 80% and in reflection with R = 5%. These large TMOKE values are mainly due to the high quality factor of TM transmittance (reflectance) resonances. The TMOKE signal for a single MO film is around 0.01%, hence an enhancement with three orders of magnitude was achieved through the fabricated structure. The reached measured TMOKE values are highly competitive with the literature where, to our knowledge, maximum values of 1.5% and 15% were experimentally demonstrated respectively through all-dielectric and magneto-plasmonic structures. Moreover, unexpected reciprocal magnetic effects were experimentally evidenced. Finally, the proposed all-dielectric structure is a low-cost device, which can be fabricated on large scale substrate, and able to enhance all the MO effects. Hence, it is a promising structure for non-destructive testing, magnetic field sensing and even biosensing

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.

碩士
國立師範大學
物理研究所
83
The surface magneto-optic Kerr effect (SMOKE) is a new probe for studying surface magnetism of ultrathin films. SMOKE is a potent- ial technique, because SMOKE can measure hysteresis curves of mo- nolayer-range magnetic films. Thus I established a SMOKE measure- ment system in the air. I tested Kerr effect of Ni(100) crystal and finished the measurement of hysteresis curves. Determining the best parameter of the measurement was also done. These provi- de for the preparation of SMOKE measurement system in ultrahigh vacuum. For fitting the UHV condition, the strength of the applied magne- tic field is inverse proportional to the gap between the magnetic poles of the electromagnet. Setting the analyzer angle to 0.3-0.7 degree will give the best signal-to-background ratio in our system. The longitudinal Kerr signal is more pronounced when the incident angle is large, at least 55 degree. However, the polar Kerr signal has opposite result. SMOKE hysteresis loops of longitudinal Kerr effect and polar Kerr effect of Ni(100) crystal are both very narrow. The behaviors of these hysteresis curve show low remanence, low coercive force and low hysteresis loss. For exploring the relationship between magnetization and structures, we intend to find the symmetry of the Ni(100) crystal by longitudinal Kerr effect. The result indicates that Kerr effect can show fourfold rotation symmtery of the Ni(100) crystal. And the easy axes of magnetization of the Ni(100) plane is along the direction of the nearest-neighor atom. The second easy axes of magnetization of the Ni(100) plane is along the direction of the second neighbor atom. The third axes of magnetization of the Ni(100) plane is along the direction of the third neighbor atom.

碩士
國立清華大學
物理系
100
This work takes advantage of Magneto-optical Kerr Effect (MOKE) to study the magnetic properties of 50-nm-thick disks grown on the /Si (100) wafer. The diameters of disks were roughly from 100 m to 650 m, which were fabricated by means of e-beam lithography, sputtering deposition and lift-off process. Our results show that the changes of magnetization direction on disks during sweep of magnetic field conform to the previous results of researches that the magnetization component perpendicular to outer magnetic field does not exist and our disks have the characteristic of vortex state, but coercivity seems to have no direct relationship with size of disks. They are all between about 15 Oe and 40 Oe. In addition, signals of hysteresis loops from our MOKE system change linearly with the area of disks.

碩士
國立清華大學
光電工程研究所
105
In this thesis, a high-sensitivity biosensor is demonstrated by exploiting surface plasma(SP) enhanced transverse magneto-optical Kerr effect(TMOKE). The size of the device is 32×22 mm2 with the prism, microfluidic system and ferromagnetic plasmonic grating integrated on a single chip with the ability to deliver and detect bio-agents systematically. The SP grating made on an optimized composite Au/Fe/Au layer exhibits a very dispersive Kerr Parameter variation near the surface plasmon resonance wavelength. After the fabricating process, we characterized the magneto optical effect of the composite ferromagnetic grating and the capabilities for detecting bio-molecules. The maximum of measured Kerr signal is about 0.04 with convert factor of 0.087 nm-1. Through this integrated system, we have demonstrated the detection of sucrose solution in low concentrations. The calculated resolution for bulk solution is about 10-6 RIU, corresponding to a minimal concentration of 0.007 %(wt). Moreover, a preliminary experimental result on studying avidin biotin interaction was also shown. The sensitivity of avidin detection in PBS solution is about 31 nM, which is limited by the fluctuation of flowing media during measurement. The whole system is potential to accomplish a compact, noncontact optical detection scheme.

碩士
國立臺灣大學
物理學研究所
87
The Magneto-Optic Kerr Effect (MOKE) has been widely used on measurements of magnetic properties of thin films. By measurements of the hysteresis loop we could decide the Curie temperature (Tc) of the film. In this thesis, we try to measure the ac susceptibility and butterfly-shaped hysteresis loop to unambiguously determine the Tc of the YIG films.

碩士
東海大學
物理學系
91
The topic of this thesis is focused on the construction of an apparatus for the magneto-optical Kerr effect (MOKE)measurement in the air, and an ultrahigh vacuum (UHV) system equipped with a surface magneto-optical Kerr effect (SMOKE) apparatus. We employed these instruments to measure the magnetic hysteresis loops of a thin film (Al2O3\V\Fe\V) with an iron thickness of 10 nm and Co/Ir(111) ultrathin films with a cobalt thickness up to 14.3 monolayers (ML). Based on the theory of magneto-optical Kerr effect, Kerr rotation θK is proportional to the magnetization of a magnetic material. Therefore, by measuring θK versus the applied magnetic field H, the magnetization curve of a magnetic material will be presented. The magnetic field was generated by an electromagnet consisted of a C-shaped silicon steel core and a Teflon coated wire. Under the condition that the generated magnetic field is proportional to the applied electric current, the maximum magnetic field could reach 2300 Oe. The spatial homogeneity within the gap of the electromagnet was optimalized. The optimal angle between Glan-Thompson polarizer and analyzer is 4.125o. All the measurements are computer controlled. In the air for the MOKE test, we obtained the magnetic hysteresis curves of an iron foil (7 mm × 5 mm × 0.7 mm). By comparing the longitudinal and polar hysteresis loops, the easy axis of the iron foil is determined to be parallel to the long axis. Afterwards, we successfully measured the magnetic hysteresis loops of a 10 nm iron thin film (Al2O3\V\Fe\V) and found an in-plane easy axis. Therefore the sensitivity of this MOKE system reaches nanometer scale. In the UHV chamber, SMOKE apparatus was employed to study the magnetic properties of ultrathin Co/Ir(111) films. The thickness of the cobalt films was determined using the AES technique. For cobalt films thinner than 3.5 ML, no hysteresis was observed. This proves that the sensitivity of this SMOKE system reaches at lease 3.5 ML of thickness. With Co thickness between 3.5 and 12.6 ML, magnetizing of the film is easier in the polar direction. As the thickness increases to above 13 ML, the easy direction for magnetizing the film changes to longitudinal direction. For films thicker than 14.3 ML, the magnetic easy axis is in the surface plane.

The morphology, composition, and magnetic properties of NiFe thin films were characterized. Films with thicknesses up to 137 nm were deposited in an RF induction evaporator at high vacuum (10^-8 mbar). Time resolved magneto-optic Kerr effect microscopy (TR-MOKE) was used to measure the Gilbert damping constant, an important dynamic magnetic property with applications to magnetic data storage. The composition of each film was measured with energy-dispersive X-ray (EDX) microscopy and used to determine the weight percent of Ni and Fe in each film. A trend of increased damping with increased thickness was found, in agreement with published results. Magnetic properties and roughness were found to differ significantly from previous films grown in the same vacuum chamber by Rudge, and are attributed to different growth modes produced by differing deposition conditions. However, the weight percent of Ni in each film was found to be inconsistent, deviating by up to 7% from the Ni80Fe20 evaporation source. Inconsistent composition, caused by the inability to control deposition parameters, prevents insight into Gilbert damping from being drawn from the analysis.
Graduate

The possibility of the existence of ferromagnetic order in Ru monolayers on the C(0001) graphite surface is studied using electron induced spin-polarized secondary electron emission (SPSEE). Below a surface Curie temperature of approximately 250K we find ferromagnetic order of the Ru monolayer. The growth mode of Ru on C(0001) is investigated by Auger electron spectroscopy (AES). We find, that the initial growth occurs laterally until a homogenous monolayer is formed. Our study provides the first observation of spontaneous, two-dimensional ferromagnetic order of a 4d transition element. To investigate the spin-polarization and domain pattern in ultrathin films and multilayers, we develop a novel technique: scanning ion microscopy with polarization analysis (SIMPA). A highly focused Ga$\sp+$-ion beam from a liquid metal ion source is moved over a sample to locally eject secondary electrons, whose spin-polarization is determined by using a medium energy Mott polarimeter. We show that the sputtering by the ion beam can be well controlled and utilized for nano-lithography and spin-resolved sputter depth profiling. We use SIMPA and the surface magneto-optic Kerr effect to study exchange coupling in Fe/Mn/Fe/Pd(100) multilayers. The intervening Mn layer is grown in a wedge shape ranging in thickness from 0 to 9 monolayers. Our results show that both Fe layers are coupled ferromagnetically for the entire Mn thickness range. Growth mode and structure are analyzed by AES and medium electron energy diffraction.

Το θέμα αυτής της διπλωματικής εργασίας είναι η παρασκευή με τη μέθοδο sputtering και ο χαρακτηρισμός μαγνητικών λεπτών υμενίων. Στo πρώτο κεφάλαιο, που αποτελεί και την εισαγωγή, γίνεται μια αναφορά στη τεχνολογία των λεπτών υμενίων και δίνεται το στοιχειώδες θεωρητικό υπόβαθρο των τεχνικών ανάπτυξης αυτών. Στο δεύτερο κεφάλαιο παρουσιάζεται η διάταξη sputtering που χρησιμοποιήθηκε για την ανάπτυξη των μαγνητικών υμενίων και δίνονται τα αποτελέσματα της βαθμονόμησης ενός μετρητικού πάχους υψηλής ακρίβειας. Το τρίτο κεφάλαιο αναφέρεται στην κατασκευή και πιστοποίηση μιας πλήρως αυτοματοποιημένης και χαμηλού κόστους διάταξης μέτρησης μαγνητικών βρόχων μέσω του φαινομένου Kerr, με μέγιστο πεδίο πόλωσης 2Τ. Το τέταρτο κεφάλαιο αναφέρεται στις πειραματικές λεπτομέρειες της παρασκευής των μαγνητικών λεπτών υμενίων Νικελίου και Κοβαλτίου και δίνονται τα αποτελέσματα του δομικού και μαγνητικού χαρακτηρισμού τους. Τέλος, στο πέμπτο κεφάλαιο, παρουσιάζονται τα συμπεράσματα και οι παρατηρήσεις που προέκυψαν κατά τη διάρκεια της ενασχόλησης με τη διπλωματική εργασία. Γίνονται, επιπλέον, και ορισμένες προτάσεις για τη μελλοντική εξέλιξη των συστημάτων sputtering και ΜΟΚΕ, ενώ τονίζεται και το τεχνολογικό ενδιαφέρον που παρουσιάζουν τα υμένια που παρασκευάσθηκαν.
The subject of this diploma thesis is the growth using the sputtering process and the characterization of thin magnetic films. The first chapter refers to thin films' technology and there is given the elementary theoretical background of the thin films’ growth. In the second chapter, there is presented the sputtering device, which is used for the growth of the magnetic films. Also, there is given the results of the calibration of a newly established thickness monitor, which is used for high accuracy thickness measurements. In the third chapter, there is given the description of the construction of a fully automatic and low cost magneto - optic Kerr effect magnetometer for the magnetic loops' measurement in a maximum magnetic field of 2T. There are, also, given the magnetic loops which are used for the construction’s certification. The fourth chapter refers to the experimental details about the preparation of the Nickel and Cobalt magnetic thin films. There are, also, given the results about the structural and magnetic characterization of the thin films. Finally, in the fifth chapter, there are presented the conclusions and the observations, which arose during the diploma thesis. There are, also, presented some proposals about the future progress of the sputtering and MOKE systems, whereas at the same, there is stressed the technical interest of the thin films, which are prepared.

Spin-polarized electron beam has not yet been produced from an unpolarized electron beam using Stern-Gerlach type spin filter, because of the Lorentz force and Heisenberg uncertainty principle. At present, electron spin detectors and filters work on the basis of spin-dependent scattering of an electron beam from crystal surfaces. Single channel efficiencies of all the spin detectors for electrons are orders of magnitudes lower than the ideal one. Specular reflection type spin-polarized low energy electron diffraction (SPLEED)-spin detectors are having higher single channel efficiencies compared to the conventional Mott detectors. Moreover, multichannel detection can be realized from specular reflection type SPLEED-spin detectors. They have higher effective efficiency than the ideal spin detector. In order to develop specular reflection type spin filter, it is important to develop a spin-polarized low energy electron diffraction system. In addition, SPLEED system allows us to study the spin-orbit and exchange scattering at crystal surfaces. The general direction of the thesis has been the development of spin-polarized low energy electron diffraction (SPLEED) system. This system has been used to investigate the spin-orbit interactions on Ir(100) surface and exchange interactions of Fe grown on Ir(100). The thesis is organized into chapters as follows. Chapter 1 introduce the reader to some of the basic concepts of polarized electrons and the evolution of spin-polarized electron sources and detectors. Sources of polarized electrons are discussed with emphasis on photocathodes such as GaAs and strained GaAs. Widely used spin detector is the Mott detector which works in the higher energy range. The working principle of the Mott detector is discussed. Commonly used spin detector in the lower energy range is the LEED detector. The concept of the LEED detector is also discussed. Working principle and recent developments of specular reflection type SPLEED spin filters are introduced. Evolution of electron spin detector is discussed towards the end of the chapter. Chapter 2 discusses about the two instruments designed and developed during the course of the thesis. The first one is a spin-polarized low energy electron diffraction system working in the reflected electron pulse counting mode in UHV. This system is capable of measuring spin asymmetries due to spin-orbit interaction and exchange interaction. This instrument is useful in understanding structure and magnetism at surfaces as well as helps to develop new spin polarimeter based on SPLEED by evaluating spin asymmetries from different surfaces. All instruments connected to SPLEED system, measurement protocol and controlling software are discussed with some details. Along with this, standard characterization tools such as X-ray diffraction and magneto-optic Kerr effect measurements are discussed. The second instrument is a novel quadratic magneto-optic Kerr effect measurement system using permanent magnets, which is simple, compact and cost-effective. We have used rotating field method to extract QMOKE component in saturation. So there is no need for precise real-time measurement of magnitude and direction of the magnetic field as in the case of vector magnet. This instrument can easily quantify QMOKE coefficients for ferrimagnetic and ferromagnetic thin films and single crystals. Chapter 3 discusses SPLEED experiments carried out on Ir(100)-(1×5)-Hex and Ir(100)-(1×2+2×1)-O surfaces. The surface structure and surface preparation techniques are discussed. The stability of the Ir(100)-(1×5)-Hex surface is evaluated by monitoring the spin asymmetry as the function of time. Within 25 hours after the surface preparation, the profile of the spin asymmetry and the reflected electron count for Ir(100)-(1×5)-Hex surface resembles that of hydrogen adsorbed Ir(100)-(1×5)-H surface. The electron energy-angle of incidence landscape of reflectivity, spin asymmetry and figure of merit are recorded for Ir(100)-(1×2+2×1)-O surface. Many wide regions with a large figure of merit are identified in the E- landscape. Chapter 4 reports SPLEED experiments carried out on Ir(100)-(1×5)-H surface. The comparison between asymmetries evaluated for the Ir(100)-(1×5)-Hex surface after 25 hours and Ir(100)-(1×5)-H surface suggests that Ir(100)-(1×5)-Hex surface is transforming to Ir(100)-(1×5)-H surface, in 25 hours. This can be due to the adsorption of more than four Langmuir of residual hydrogen during this time. The energy-angle landscape of reflectivity, asymmetry and figure of merit are recorded for Ir(100)-(1×5)-H surface in an energy range 20 eV to 100 eV and angle range 10 to 60 . Many regions are identified as the working point for specular reflection type spin filter based on SPLEED. The surface structure and surface preparation techniques are discussed. The stability of the surface is also evaluated. Chapter 5 investigates the growth and magnetic properties of Fe(100) film on Ir(100)-(1×1), Ir(100)-(1×5)-Hex and Ir(100)-(1×2+2×1)-O surfaces. LEED, MEED, LMOKE and QMOKE studies were presented. The growth is found to be layer-by-layer at least up to 20 monolayers (ML) at room temperature. At higher deposition temperature, the MEED oscillations disappear around 3-5 ML. Magnetic anisotropy of the Fe(100) film grown on Ir(100)-(1×2+2×1)-O surfaces is evaluated using LMOKE measurement using Kerr microscope. Simultaneous in-situ LMOKE and MEED measurements were carried out during the deposition. Ferromagnetic ordering with an in-plane easy axis starts above 4.5 ML at room temperature. The Kerr rotation normalized by thickness is evaluated in the pseudomorphic regime and strain relaxed regime. The probing depth of the MOKE is found to be around 14 nm in Fe(100)/Ir(100). An antisymmetric component is observed in the re-magnetization loop measured using MOKE. This antisymmetric loop arises due to the quadratic magneto-optic coupling which is separated by symmetrization and antisymmetrization procedure. The observed quadratic magneto-optic coupling suggests that the analysis based on the assumption that the magneto-optic coupling is linear in magnetization has to be modified. In order to quantify the quadratic magneto-optic coupling parameters, a QMOKE measurement system is developed and measurements were carried out. Chapter 6 discusses SPLEED experiments carried out on various thicknesses of Fe(100) film. Fe(100) films grown on Ir(100) substrate with the thickness less than or equal to 4 ML is not ferromagnetic with in-plane easy axis at room temperature. The non-zero exchange asymmetry observed for 5 ML and above indicates the presence of ferromagnetic ordering. A difference in the profile of exchange asymmetry is observed between pseudomorphic and strain relaxed regime. Large spin-orbit asymmetry is observed for 1 ML and 2 ML Fe(100) which is unexpected from a low atomic number (Z) material. The reason for large spin-orbit asymmetry is still unknown. The energy-angle landscape of reflectivity, exchange asymmetry, spin-orbit asymmetry and figure of merit were evaluated for 21 ML of Fe(100). Many working points were identified for different types multichannel spin filter based on exchange interaction Finally, the various results are summarized and a broad outlook is given.