Academic literature on the topic 'Magneto-optic Kerr Effect (MOKE)'

Magneto-optic Kerr effect (MOKE) microscopy is a widely used technique for observation and characterization of microscopic magnetic structures. While being efficient and easy-to-use, current commercial MOKE microscopes are not superb in time resolution, limited by the frame rate of the camera. Here, we introduce a revolutionary sensor, namely, the event camera, as a convenient add-on to traditional MOKE microscopy and explore the potential applications of event-based vision in research areas using MOKE microscopy. We use the frame stacking method to improve visibility to human eyes in generated slow motion videos. We perform a proof-of-principle feedback control experiment using the event-based vision data and characterize the overall latency of the feedback loop as short as 25 ms with our current prototype. Finally, we discuss the limitations of current event cameras in MOKE microscopy as well.

Magneto-optic Kerr effect (MOKE) enhancement is studied for Yttrium Iron Garnet (YIG) nanoparticle. The MOKE is quantified by the ratio of the polarization components of reflected wave, namely between the perpendicular component to the parallel component with respect to the polarization of the incident wave. Thus, the enhancement of MOKE can be obtained by increasing the perpendicular component or reducing the parallel component of the reflected wave polarization. An FDTD calculation is performed to obtain the scattered field. Projecting the resulting scattered field to the vector spherical harmonic basis, we show through multipole moments analysis that the suppression of backscattering non-MO field and the raise of the backscattered MO field can be achieved by subtle superposition of some optical modes. For the specific YIG particle system and the wavelength range chosen, the result shows that enhancement of MOKE up to 7.5[Formula: see text]mrad can be achieved.

Magnetic multilayer with large perpendicular magnetic anisotropy (PMA) has attracted sustained interest owing to its importance to fundamental physics and applications. In this work, the high quality of Pt/Co/Pt heterostructures with large PMA was successfully achieved to exhibit a large anomalous Hall effect (AHE) with squared Hall loops. By calculating the proportional relationship between the longitudinal resistivity (ρxx) and the abnormal Hall coefficient (Rs), it is confirmed that the basic mechanism of AHE comes from the external skew scattering (SS) and side jump (SJ), while SS contribution, related to asymmetric scattering from impurities, is dominant in the AHE. Furthermore, the obvious magneto-optical Kerr effect (MOKE) was also observed using the polar MOKE microscopy. The obviously circular magnetic domain can form and propagate in response to the applied out-of-plane magnetic field, resulting in the magnetization reversal of the entire film. This work offers important information in terms of both AHE and MOKE in the ultrathin ferromagnetic films with perpendicular anisotropy, establishing the application foundation for the nonvolatile memories and spintronics.

The fast-emerging diverse applications using a variety of magnetic/non-magnetic heterostructure ultra-thin films warrant the sensitive characterization of the electrical, optical, and magnetic properties of the interface. As a practical alternate to the conventional magneto-optic Kerr effect (MOKE) method, we propose and demonstrate the spin-Hall effect of the light (SHEL)-based MOKE method with competitive sensitivity and scope for further improvement. The SHEL-MOKE technique is a versatile surface characterization tool for studying materials’ magnetic and dielectric ordering, which are extracted from the variations to the phase-polarization characteristics of a focused beam of light reflected at the interface, as a function of the applied magnetic field. Using this technique, we measure the magnetic field dependent complex Kerr angle and the coercivity in ultra-thin films of permalloy (Py) and at molybdenum disulfide (MoS[Formula: see text])—permalloy (MSPy) hetero-structure interfaces. A comprehensive theoretical model and simulation data are provided to strengthen the potential of this simple non-invasive optical method. The theoretical model is subsequently applied to extract the optical conductivity of non-magnetic ultra-thin layers of MoS[Formula: see text].

(300Å)Fe films were deposited, on MgO (001) single crystalline substrate with various buffer layer thickness tAg (Å) / (75Å) Cr. The magnetic properties of the Fe films were measured by magneto-optic Kerr effect (MOKE) technique. The MOKE measurements provided the tAg buffer layer thickness dependence of the hysteresis loops and the change of loop shapes with the surface roughness. It was found that the magnetization reversal process changed with the surface roughness. Magnetization rotation dominated the magnetization reversal for the smoothest films. As the films roughened, the domain-wall pinning set in, eventually dominating the magnetization reversal for the roughest films. Additionally, the magnetic uniaxial anisotropy in the Fe films disappeared as the roughness parameters increased. It was also found from MOKE that the surface roughness strongly affected the coercivity.

The magneto-optical Kerr effect (MOKE) for both Heusler type alloys (AuMnSb and AuMnSn) were studied using the full-potential linearized augmented plane-wave (FP-LAPW) method, based on the density functional theory implemented in the WIEN2k code. The differences with previous calculations on the Kerr spectra have been found explicitly. At proper Lorentzian such asδ= 0.4 eV, the calculated Kerr angle of AuMnSn reaches its maxima +0.3° near 0.6 eV and-0.5° at 5.2 eV, respectively while the MOKE spectra of AuMnSb exhibit less prominent Peaks (+0.5° at 0.3 eV, -1.9° at 0.9 eV, -1.0° at 2.4 eV and-2.0° at 5.3 eV). The results on the spectra in this work showed quite a lot differences with all previous all-electron calculations. It is concluded that the contribution from Sb (or Sn) site to the magneto-optical kerr effect is quite crucial in Heuslar alloys.

The magneto-optical Kerr effect (MOKE) refers to the rotation of the polarization plane when a linearly polarized light is reflected at the surface of magnetic material. The MOKE reveals the magnetization of the optical properties of magnetic material and can be characterized by the dielectric tensor containing the magneto-optical constant. Thus, exploring the MOKE requires very precise determination of the magneto-optical constant. The photonic spin Hall effect (PSHE), which corresponds to the lateral and in-plane spin-dependent splitting of the beam, can be used as an effective method to characterize the magneto-optical constant due to its advantage of being extremely sensitive to changes in the physical parameters of the material. Most of the previous studies only considered the case of a single thickness of magnetic material and a single MOKE and need to introduce complex weak measurement techniques to observe the photonic spin Hall effect. In this work, we theoretically investigate the in-plane spin angular shifts in three MOKE cases in bulk and ultrathin magnetic materials. We can effectively tune the in-plane angular displacements of different magnetic material thickness by changing the magnetic field direction corresponding to different MOKEs and changing the magneto-optical constants (including amplitude and phase). The research results show that in the case of bulk and ultrathin magnetic materials, the internal spin angular displacements under different MOKEs will show different trends when the magneto-optical constants change the amplitude and phase, especially in ultra-thin magnetic material. In the lateral Kerr effect in thin material, the photon in-plane angular displacement does not affect the change of the magneto-optical constant, but in other cases, the amplitude relative to the phase has a much larger effect on the photon in-plane angular displacement. In this regard, we propose a new method which can directly determine the amplitude and phase of the magneto-optical constant by using the huge in-plane spin angular displacement without considering the weak measurements and can also judge different MOKEs according to the variation of the in-plane angular displacement in the bulk and ultrathin magnetic materials. This method not only provides a new probe for measuring magneto-optical constants but also expands the study of spin photonics.

The magneto-optical Kerr effect (MOKE) has recently been achieved on non-ferromagnetic metals by injecting spin currents. To use the magneto-optical Kerr effect as a quantitative tool, it is crucial to study the relationship between the Kerr rotation angle and the spin accumulation on non-ferromagnets. In this work, I measure a transient magneto-optical Kerr rotation on non-ferromagnetic metals of Cu, Au, and Pt driven by an ultrafast spin current from an adjacent ferromagnetic metal. Through comparing the measured Kerr rotation and the calculated spin accumulation, I determine the conversion ratio between the Kerr rotation and the spin accumulation to be: −4 × 10−9 (real part), −2.5 × 10−8 (real part), and −3 × 10−9 (imaginary part) rad m A−1 for Cu, Au, and Pt, respectively, at a wavelength of 784 nm.

We report on an all-optical investigation of coupled spin excitation modes in a series of magnetic trilayer structures. Using time-resolved magneto-optic Kerr effect (tr-MOKE) magnetometry, we observe multi-mode coherent spin excitations in [Formula: see text]/Ru/[Formula: see text] multilayers even though the tr-MOKE optical detection is sensitive only to the [Formula: see text] magnetization dynamics. Frequency shifts of the different modes indicate that the coupling between the [Formula: see text] and [Formula: see text] layers varies from anti-ferromagnetic to ferromagnetic to uncoupled as the Ru spacer layer thickness is increased from 8 Å to 200 Å. The lifetime of the high frequency coherent oscillations in the [Formula: see text] layer increases by over 200%–300% even in the case of uncoupled [Formula: see text] and [Formula: see text] layers with a 200 Å thick Ru spacer. The results suggest an additional method to decrease the damping of high-moment alloys in layered magnetic nanostructures.

Nanoporous Co40Fe40B20 (CoFeB) and sandwich tungsten (W)/CoFeB/W thin films were fabricated via an anodic aluminum oxide (AAO) template-assisted magneto sputtering process. Their thickness-dependent magneto-optical Kerr effect (MOKE) hysteresis loops were investigated for enhanced Kerr rotation. Control of the Kerr null points of the polarized reflected light can be realized via the thicknesses of the CoFeB layers and W layers. Simulation of the thickness-dependent phase difference change by the finite element method reveals the existence of the two Kerr null points for W/CoFeB/W thin films, matching the experimental result very well. However, there are two additional Kerr null points for pure CoFeB thin films according to the simulation by comparing with the experimental result (only one). Theoretical analysis indicates that the different Kerr null points between the experimental result and the simulation are mainly due to the enhanced inner magnetization in the ferromagnetic CoFeB layer with the increased thickness, which is usually omitted in the simulation. Clearly, the introduction of non-ferromagnetic W layers can experimentally regulate the Kerr null points of ferromagnetic thin films. Moreover, construction of W/CoFeB/W sandwich thin films can greatly increase the highest magneto-optical susceptibility and the saturated Kerr rotation angle when compared with CoFeB thin films of the same thickness.

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.

We present a time-resolved Kerr microscope, capable of measuring the magnetization dynamics of samples grown on transparent, double-side-polished substrates.The magnetization is excited by a current pulse, using a coplanar waveguide placed beneath the samples. The Kerr rotation is detected with the stroboscopic pump-probe technique, using a probing laser, synchronized with the current pulse.We report benchmark measurements of the time-resolved Kerr instrument for magnetization dynamics in thin permalloy and FePd films. The experimental results for ferromagnetic resonance peaks have been compared with the values predicted by Kittel.
Vi presenterar ett tidsupplöst Kerr-mikroskop, kapabel till att mäta magnetiseringsdynamiken hos magnetiska prov tillverkade på transparenta, dubbelsdigt polerade substrat. Magnetiseringen exiteras med en strömpuls via en koplanär vågguide placerad under provet. Kerr-rotationen detekteras med hjälp av en stroboskopisk ”pump-probe” teknik som använder en ”probing” laser synchroniserad med strömpulsen. Vi rapporterar prestandatest av det tidsupplösta kerr-instrumentet för magnetiseringsdynamiken i tunna permalloy - och FePd - filmer. De experimentella resultaten för de ferromagnetiska resonans-peakarna har jämförts med beräknade värden från Kittel.

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

Due to the ever-increasing worldwide consumption of memory for digital information, new technologies for higher capacity and faster data storage systems have been the focus of research and development. A step towards achieving higher data storage densities or magnetic recording media is the concept of bit patterned media, where the magnetic recording layer is divided up into magnetically isolated bit units. This approach is one of the most promising technologies for increasing data storage densities and could be implemented by nanostructuring the wafer. Therefore, the fabrication of the appropriate nanostructures on a small scale and then be able to manufacture these structures on an industrial scale is one of the problems where science and industry are working on a solution. In addition, the answer to the open question about the influence that patterning on the nano length scale has on the magnetic properties is of great interest. The main goal of this thesis is to answer the open question, which magnetic properties can be tailored by a modification of the surface texture on the nanometre length scale. For this purpose the following properties: anisotropy, remanence, coercivity, switching field distribution, saturation magnetisation, Gilbert damping, and inhomogeneous linebroadening were compared between planar two dimensional thin ferromagnetic films and three dimensional magnetic structures. In addition, the influences of the tailored morphology on the intergranular or the exchange coupling between the structures, which is called interdot exchange coupling, was investigated. For the ferromagnetic thin films, the focus of the investigations was on the granular CoCrPt:SiO2 and [Co/Pd] layer, which currently are the state-of-the-art material for magnetic data storage media. These materials are characterised by their high coercivity and high perpendicular anisotropy, which has a low spatial distribution in the preferred direction of magnetisation. In this work the pre-structured GaSb(001) substrate with self-assembled periodic nanocone structures at the surface are used. The preparation by ion beam erosion of these structures is simple, fast, and highly reproducible and therefore this method is particularly beneficial for fundamental research. To compare the 2D thin films with the 3D magnetic structures, besides the pre-structured specimen, planar samples were also fabricated. The first sample series prepared was coated by Py. Due to the fact that the magnetic properties of this material are well-known, it was also possible to do some OOMMF simulations in addition to the VNA-FMR and MOKE measurements. Afterwards two planar samples with CoCrPt and CoCrPt:SiO2 were prepared. The planar CoCrPt:SiO2 samples were Co+ ion implanted to study the influence of such irradiation on the intergranular and interdot exchange coupling, switching field distribution, and in particular on the spin dynamics. Moreover, both samples were measured by TRMOKE in order to obtain information about the spin dynamics. Subsequently, the perpendicular storage media materials CoCrPt:SiO2 and [Co/Pd] were deposited on a prestructured GaSb(001) nanocone substrate surface. These sample series were measured by MOKE, SQUID, and vector-VSM. The measurements demonstrate the influence of the periodicity and height of the nanocones on the intergranular and interdot exchange coupling. They also show the reorientation of the magnetisation with respect to the curvature of the substrate template and furthermore, the morphology-induced influences on the magnetic domains. From the comparison between the results for the planar and the pre-structured samples, a decrease of the interdot exchange coupling was observed, which scales together with the periodicity of the nanocone pattern. In addition, it was shown that for all samples with thin magnetic films on nanocones,the magnetisation aligns along the curvature of the underlying nanocone structure. For Py on nanocones, planar granular CoCrPt:SiO2, and planar granular CoCrPt, measurements by VNA-FMR and TRMOKE could be carried out, which yielded information about the spin dynamics. The results obtained for both of the planar sample are comparable to values from the literature for the Gilbert damping. The results for the Py samples showed that the commonly used 2D model resonance condition is, in case of a 3D magnetic structure, no longer valid due to the alignment of the magnetisation along the underlying substrate structure and therefore an new model has to be derived
Aufgrund des weltweiten, immer weiter steigenden Bedarfs an Speicherplatz von digitalen Information, sind neue Technologien für größere und schnellere Speichermedien im Fokus von Forschung und Entwicklung. Ein Schritt hin zu einer höheren Speicherdichte in der magnetischen Datenspeicherung ist dabei das sogenannte Konzept der ”Bit patterned media”, das definierte Informationseinheiten auf regelmäßig angeordneten Nanostrukturen beschreibt. Dieser Ansatz ist einer der derzeit vielversprechendsten Optionen die Speicherdichte zu erhöhen. Dabei ist die Herstellung der benötigten Nanostrukturen und deren Skalierung hin zu makroskopischen Dimensionen eines der Probleme an deren Lösung die Wissenschaft und Industrie derzeit arbeitet. Desweiteren ist die Antwort auf die noch offene Frage nach der Beeinflussung der nanoskaligen Strukturen auf die magnetischen Eigenschaften von großem Interesse. Das Hauptziel in dieser Arbeit ist es, einen Beitrag zur Beantwortung der Frage, welche magnetischen Eigenschaften sich durch eine Veränderung der Oberflächenstruktur im Nanometerbereich beeinflussen lassen, zu leisten. Hierzu wurden die folgenden Eigenschaften, wie zum Beispiel die Anisotropie, Remanenz,Koerzitivität, Schaltfeldverteilung, Sättigungsmagnetisierung, Gilbertdämpfung und inhomogene Linienverbreiterung von planaren zweidimensionalen dünnen ferromagnetische Schichten mit denen von dreidimensionalen magnetischen Strukturen verglichen. Zusätzlich wurde der Einfluss der angegpassten Morphologie auf die intergranularen- beziehungsweise auf die zwischen den Strukturen wirkende (interdot) Austauschkopplung untersucht. Der Hauptaugenmerk bei den ferromagnetisch dünnen Schichten lag dabei auf den granularen CoCrPt:SiO2 und [Co/Pd] Filmen, die heutzutage ein Standardmaterial für die magnetischen Speichermedien darstellen. Diese Materialien zeichnen sich durch eine hohe Koerzivität und senkrechte Anisotropie, mit geringer räumlicher Verteilung der Vorzugsrichtung der Magnetisierung, aus. Die hier vorgestellten vorstrukturierten GaSb(001) Substrate mit selbstordnenden periodischen Nanokegeln auf der Oberfläche, sind mittels Ionenstrahlerosion einfach, schnell und sehr gut reproduzierbar herzustellen. Deshalb ist diese Methode besonders für die Grundlagenforschung von Vorteil. Um einen Vergleich zwischen 2D Filmen und 3D Strukturen ziehen zu können, wurden neben den vorstrukturierten Substraten auch planare Proben beschichtet. Eine erste Versuchsreihe wurde mit einem dünnen Py Film präpariert. Da dessen magnetische Eigenschaften wohlbekannt sind, konnten neben den Untersuchungen mit VNA-FMR und MOKE auch einige OOMF Simulationen erstellt werden. Danach wurden zwei Proben mit planarem CoCrPt beziehungsweise CoCrPt:SiO2 untersucht. Bei den planaren CoCrPt:SiO2 Proben wurden außerdem noch Co+ Ionen implantiert, um deren Auswirkungen auf die intergranulare Austauschkopplung, Schaltfeldverteilung und besonders auf die Spindynamik zu bestimmen. Bei beiden Probensystemen konnte zusätzlich die Spindynamik mittels zeitaufgelöstem MOKE gemessen werden. Im Anschluss wurden die beiden senkrechten Speichermedien CoCrPt:SiO2 and [Co/Pd] auf Substraten mit Nanokegeln vorstrukturierten GaSb(001) Oberflächen abgeschieden. Diese Proben wurden mit MFM, MOKE, SQUID und Vektor-VSM vermessen. Aus den Messungen konnnten dann die Einflüsse auf die intergranulare- beziehungsweise interdot Austauschkopplung in Abhängigkeit von der Periodizität und Höhe der Nanokegel bestimmt werden, sowie die Umorientierung der Magnetisierung bezüglich der Substratkrümmung und den Morphologie induzierten Einfluss auf die magnetischen Domänen. Anhand der Vergleiche zwischen den Messungen der planaren und den vorstrukturierten Proben konnte eine Verringerung der Austauschkopplung zwischen den Strukturen gezeigt werden, die mit der Nanokegelstrukturperiodizität skaliert. Außerdem wurde in allen dünnen magnetischen Filmen auf Nanokegeln gezeigt, dass die Magnetisierung sich in Abhängigkeit der darunterliegenden Struktur ausrichtet. Bei den Py auf Nanokegeln, den planaren CoCrPt und dem planaren CoCrPt:SiO2 Proben konnten außerdem mit VNA-FMR und TRMOKE Informationen bezüglich der Spindynamik gemessen werden. Die erzielten Ergebnisse, der beiden planaren Proben, sind vergleichbar mit denen, aus der Literatur bekannten Werten, für die Gilbertdämpfung. Darüber hinaus wurde durch die Messungen an den Py Proben gezeigt, dass die Theorie, des bisher genutzten 2D Modells, nicht mehr gültig ist, da sich die Magnetisierung entlang der Substratstruktur ausrichtet, und deshalb ein neues Model aufgestellt werden muss

Due to the ever-increasing worldwide consumption of memory for digital information, new technologies for higher capacity and faster data storage systems have been the focus of research and development. A step towards achieving higher data storage densities or magnetic recording media is the concept of bit patterned media, where the magnetic recording layer is divided up into magnetically isolated bit units. This approach is one of the most promising technologies for increasing data storage densities and could be implemented by nanostructuring the wafer. Therefore, the fabrication of the appropriate nanostructures on a small scale and then be able to manufacture these structures on an industrial scale is one of the problems where science and industry are working on a solution. In addition, the answer to the open question about the influence that patterning on the nano length scale has on the magnetic properties is of great interest. The main goal of this thesis is to answer the open question, which magnetic properties can be tailored by a modification of the surface texture on the nanometre length scale. For this purpose the following properties: anisotropy, remanence, coercivity, switching field distribution, saturation magnetisation, Gilbert damping, and inhomogeneous linebroadening were compared between planar two dimensional thin ferromagnetic films and three dimensional magnetic structures. In addition, the influences of the tailored morphology on the intergranular or the exchange coupling between the structures, which is called interdot exchange coupling, was investigated. For the ferromagnetic thin films, the focus of the investigations was on the granular CoCrPt:SiO2 and [Co/Pd] layer, which currently are the state-of-the-art material for magnetic data storage media. These materials are characterised by their high coercivity and high perpendicular anisotropy, which has a low spatial distribution in the preferred direction of magnetisation. In this work the pre-structured GaSb(001) substrate with self-assembled periodic nanocone structures at the surface are used. The preparation by ion beam erosion of these structures is simple, fast, and highly reproducible and therefore this method is particularly beneficial for fundamental research. To compare the 2D thin films with the 3D magnetic structures, besides the pre-structured specimen, planar samples were also fabricated. The first sample series prepared was coated by Py. Due to the fact that the magnetic properties of this material are well-known, it was also possible to do some OOMMF simulations in addition to the VNA-FMR and MOKE measurements. Afterwards two planar samples with CoCrPt and CoCrPt:SiO2 were prepared. The planar CoCrPt:SiO2 samples were Co+ ion implanted to study the influence of such irradiation on the intergranular and interdot exchange coupling, switching field distribution, and in particular on the spin dynamics. Moreover, both samples were measured by TRMOKE in order to obtain information about the spin dynamics. Subsequently, the perpendicular storage media materials CoCrPt:SiO2 and [Co/Pd] were deposited on a prestructured GaSb(001) nanocone substrate surface. These sample series were measured by MOKE, SQUID, and vector-VSM. The measurements demonstrate the influence of the periodicity and height of the nanocones on the intergranular and interdot exchange coupling. They also show the reorientation of the magnetisation with respect to the curvature of the substrate template and furthermore, the morphology-induced influences on the magnetic domains. From the comparison between the results for the planar and the pre-structured samples, a decrease of the interdot exchange coupling was observed, which scales together with the periodicity of the nanocone pattern. In addition, it was shown that for all samples with thin magnetic films on nanocones,the magnetisation aligns along the curvature of the underlying nanocone structure. For Py on nanocones, planar granular CoCrPt:SiO2, and planar granular CoCrPt, measurements by VNA-FMR and TRMOKE could be carried out, which yielded information about the spin dynamics. The results obtained for both of the planar sample are comparable to values from the literature for the Gilbert damping. The results for the Py samples showed that the commonly used 2D model resonance condition is, in case of a 3D magnetic structure, no longer valid due to the alignment of the magnetisation along the underlying substrate structure and therefore an new model has to be derived.
Aufgrund des weltweiten, immer weiter steigenden Bedarfs an Speicherplatz von digitalen Information, sind neue Technologien für größere und schnellere Speichermedien im Fokus von Forschung und Entwicklung. Ein Schritt hin zu einer höheren Speicherdichte in der magnetischen Datenspeicherung ist dabei das sogenannte Konzept der ”Bit patterned media”, das definierte Informationseinheiten auf regelmäßig angeordneten Nanostrukturen beschreibt. Dieser Ansatz ist einer der derzeit vielversprechendsten Optionen die Speicherdichte zu erhöhen. Dabei ist die Herstellung der benötigten Nanostrukturen und deren Skalierung hin zu makroskopischen Dimensionen eines der Probleme an deren Lösung die Wissenschaft und Industrie derzeit arbeitet. Desweiteren ist die Antwort auf die noch offene Frage nach der Beeinflussung der nanoskaligen Strukturen auf die magnetischen Eigenschaften von großem Interesse. Das Hauptziel in dieser Arbeit ist es, einen Beitrag zur Beantwortung der Frage, welche magnetischen Eigenschaften sich durch eine Veränderung der Oberflächenstruktur im Nanometerbereich beeinflussen lassen, zu leisten. Hierzu wurden die folgenden Eigenschaften, wie zum Beispiel die Anisotropie, Remanenz,Koerzitivität, Schaltfeldverteilung, Sättigungsmagnetisierung, Gilbertdämpfung und inhomogene Linienverbreiterung von planaren zweidimensionalen dünnen ferromagnetische Schichten mit denen von dreidimensionalen magnetischen Strukturen verglichen. Zusätzlich wurde der Einfluss der angegpassten Morphologie auf die intergranularen- beziehungsweise auf die zwischen den Strukturen wirkende (interdot) Austauschkopplung untersucht. Der Hauptaugenmerk bei den ferromagnetisch dünnen Schichten lag dabei auf den granularen CoCrPt:SiO2 und [Co/Pd] Filmen, die heutzutage ein Standardmaterial für die magnetischen Speichermedien darstellen. Diese Materialien zeichnen sich durch eine hohe Koerzivität und senkrechte Anisotropie, mit geringer räumlicher Verteilung der Vorzugsrichtung der Magnetisierung, aus. Die hier vorgestellten vorstrukturierten GaSb(001) Substrate mit selbstordnenden periodischen Nanokegeln auf der Oberfläche, sind mittels Ionenstrahlerosion einfach, schnell und sehr gut reproduzierbar herzustellen. Deshalb ist diese Methode besonders für die Grundlagenforschung von Vorteil. Um einen Vergleich zwischen 2D Filmen und 3D Strukturen ziehen zu können, wurden neben den vorstrukturierten Substraten auch planare Proben beschichtet. Eine erste Versuchsreihe wurde mit einem dünnen Py Film präpariert. Da dessen magnetische Eigenschaften wohlbekannt sind, konnten neben den Untersuchungen mit VNA-FMR und MOKE auch einige OOMF Simulationen erstellt werden. Danach wurden zwei Proben mit planarem CoCrPt beziehungsweise CoCrPt:SiO2 untersucht. Bei den planaren CoCrPt:SiO2 Proben wurden außerdem noch Co+ Ionen implantiert, um deren Auswirkungen auf die intergranulare Austauschkopplung, Schaltfeldverteilung und besonders auf die Spindynamik zu bestimmen. Bei beiden Probensystemen konnte zusätzlich die Spindynamik mittels zeitaufgelöstem MOKE gemessen werden. Im Anschluss wurden die beiden senkrechten Speichermedien CoCrPt:SiO2 and [Co/Pd] auf Substraten mit Nanokegeln vorstrukturierten GaSb(001) Oberflächen abgeschieden. Diese Proben wurden mit MFM, MOKE, SQUID und Vektor-VSM vermessen. Aus den Messungen konnnten dann die Einflüsse auf die intergranulare- beziehungsweise interdot Austauschkopplung in Abhängigkeit von der Periodizität und Höhe der Nanokegel bestimmt werden, sowie die Umorientierung der Magnetisierung bezüglich der Substratkrümmung und den Morphologie induzierten Einfluss auf die magnetischen Domänen. Anhand der Vergleiche zwischen den Messungen der planaren und den vorstrukturierten Proben konnte eine Verringerung der Austauschkopplung zwischen den Strukturen gezeigt werden, die mit der Nanokegelstrukturperiodizität skaliert. Außerdem wurde in allen dünnen magnetischen Filmen auf Nanokegeln gezeigt, dass die Magnetisierung sich in Abhängigkeit der darunterliegenden Struktur ausrichtet. Bei den Py auf Nanokegeln, den planaren CoCrPt und dem planaren CoCrPt:SiO2 Proben konnten außerdem mit VNA-FMR und TRMOKE Informationen bezüglich der Spindynamik gemessen werden. Die erzielten Ergebnisse, der beiden planaren Proben, sind vergleichbar mit denen, aus der Literatur bekannten Werten, für die Gilbertdämpfung. Darüber hinaus wurde durch die Messungen an den Py Proben gezeigt, dass die Theorie, des bisher genutzten 2D Modells, nicht mehr gültig ist, da sich die Magnetisierung entlang der Substratstruktur ausrichtet, und deshalb ein neues Model aufgestellt werden muss.

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.

The magneto-optic properties of interest are the Faraday Effect, Kerr Rotation, and the Cotton–Mouton Effect. In 1846, Michael Faraday discovered that when linearly polarized light passes through glass in the presence of a magnetic field, the plane of polarization is rotated. The Faraday Effect is now used in a variety of microwave and optical devices. Normally the Faraday experiment is carried out in transmission, but rotation also occurs in reflection, the so-called Kerr Rotation that is used in magneto-optic disks with Mbit storage capability. Other magneto-optic phenomena of less practical interest include the Cotton– Mouton Effect, a quadratic relationship between birefringence and magnetic field, and magnetic circular dichroism that is closely related to the Faraday Effect. A number of nonlinear optical effects of magnetic or magnetoelectric origin are also under study. Almost all these magnetooptical effects are caused by the splitting of electronic energy levels by a magnetic field. This splitting was first discovered by the Dutch physicist Zeeman in 1896, and is referred to as the Zeeman Effect. When linearly polarized light travels parallel to a magnetic field, the plane of polarization is rotated through an angle ψ. It is found that the angle of rotation is given by . . . ψ(ω) = V(ω)Ht, . . . where H is the applied magnetic field, t is the sample thickness, ω is the angular frequency of the electromagnetic wave, and V(ω) is the Verdet coefficient. Faraday rotation is observed in nonmagnetic materials as well as in ferromagnets. The Verdet coefficient of a commercial one-way glass is plotted as a function of wavelength in Fig. 31.1(a). Corning 8363 is a rare earth borate glass developed to remove reflections from optical systems. A polarized laser beam is transmitted through the glass parallel to the applied magnetic field. The plane of polarization is rotated 45◦ by the Faraday Effect. The transmitted beam passes through the analyzer that is set at 45◦ to the polarizer. But the reflected waves coming from the surface of the glass and from the analyzer are rotated another 45◦ as they return toward the laser.

It is well-known that the origin of the magneto-optical Kerr effect (MOKE) is spin-orbit coupling of electrons. The effect is relatively small in the visible light region because of the weak spin-orbit coupling of conduction electrons. On the other hand, the effect can be enhanced significantly in the x-ray region by tuning the x-ray energy through some core electron absorption edges of the sample, since the spin-orbit coupling can be much stronger for these core-electrons.

The nonlinear Magneto-optical Second Harmonie Generation (MSHG, also called NOMOKE for NOnlinear MOKE) derives its specific interface magnetisation sensitivity from the magnetisation (M) dependent second order ±χ(2)(± M) tensor [1]. Indeed, the comparison of measurements taken on Au/Co/Au and Pt/Co/Pt structures using both MSHG and the bulk magnetisation sensitive Magneto-Optical Kerr Effect (MOKE) in longitudinal configuration exhibit interesting differences, showing the interface sensitivity of MSHG.

In erasable optical storage, the requirements for writing, read and erasure processes to the distribution of the optical field and the time-space distribution of the temperature field induced by pulse laser are harsher than those in nonerasable optical storage. So, it is highly necessary to consider about parameters in optics, thermology and structure, latent heat effect (phase-change model), magneto-optic Kerr and Faraday effects (magneto-optic model), etc. more carefully and all-sidedly in designing the distributions of optical field and heat field.

Antireflective thin film structures(1) have been used advantageously in write – once(2)(3) and reversible phase change(4) materials design to provide increased sensitivity, better marking contrast and to amplify the optical effects of small laser-induced marking effects. The same structures may be used in magneto-optic recording to increase the shot-noise-limited figure of merit R½ΘK for Kerr readout. Previous reports have analyzed the effects of single quarter-wave overlayers(5) and more powerful approaches such as the encapsulated trilayer (quadrilayer)(6). This paper will present a comprehensive analysis of the various approaches to antireflection structures and their relative enhancement capabilities for shot noise limited magneto-optic readout.