High density recording by magnetic field modulation on FAD media with a land/groove substrate using the MFM method was investigated. A sufficient power margin was obtained at a density of 2.81 Gbit/inch² for a land/groove substrate with 1.7-μm track pitch. In the case of a 1.6-μm track pitch, which corresponds to a density of 2.99 Gbit/inch², the read/write charcteristics were almost the same as that of the 1.7-μm track pitch except for the power margin which was limited by the crosstalk from the adjacent tracks.

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  Comparison is made between the experimental and theoretical behaviour of the optical and magneto-optical properties of a series of Co-SiO₂ films in which the volume fraction q occupied by the particles is varied between 0.4 and 0.8. A modified Maxwell Garnett model allows for oxidation of the cobalt particles in addition to the effect of reduced electron mean free path reported previously [1].

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  The transition property of the magnetization direction, from in-plane to perpendicular, is one of the most important parameters for CAD-MSR double layered films. We found that both SiN under layer etching and a lower Ar gas pressure during deposition of the reading layer make the θ_K - T curve steeper. The reason for the improvement in the θ_K - T curve is the flattened surface and large perpendicular anisotropy of the reading layer. This would improve the resolution of the CAD-MSR because of clear mask formation.

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  New magnetic configurations in 2D and 3D artificial lattices are studied by solving the non-linear equation based on the classical Heisenberg models for 2D and 3D artificial lattices. The results indicate strong possibility to be used as an ultra-high density magnetic recording media achieved by magnetic multi-valued(MMV) recording. The MMV states are based on the magnetic anisotropic configurations in 2D and 3D artificial lattices, because establishing the MMV states is considered necessary to make different magnetic domains.

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  It has been predicted theoretically that a metal/dielectric multilayer system would possess an enhanced figure of merit over the usual metal/metal systems, such as Co/Pt, due to the much reduced optical absorption in the dielectric layer. A series of Co/AlN and Co/Pt/AlN/Pt multilayer thin films have been fabricated using sputter-deposition. The magnetic and magneto-optic properties have been analysed and an attempt has been made to correlate these with the observed microstructure. It would appear that the magnetic properties of the multilayers prepared and investigated in this work make them unsuitable for use as a magneto-optic recording medium due to a lack of the essential large perpendicular anisotropy.

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  Transmission electron microscopy has been used to study the micromagnetic reversal mechanism in CoNi/Pt multilayers. Magnetisation reversal proceeds by nucleation at a small number of sites followed by domain wall branching to form an irregular dendritic domain structure. A substantial increase in field strength is required to eliminate the domains. Annealing at 300°C in vacuum leads to increased coercivity and a change in time dependent effects during the initial part of the reversal process.

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  First-principles calculations of the magnetocrystalline anisotropy energy have been performed and it is predicted that the perpendicular magnetic anisotropy energy of a Au/(Fe-Co)(111) multilayer will be lager than that of a Au/Co multilayer. This multilayer was then grown by MBE method and found to have the predicted properties. The surface magnetic anisotropy energy is 0.64 mJ/m², which is larger than the value reported previously for the Au/Co multilayer by 10%. The result indicates the possibility to control the magnetic anisotropy by changing the bandfilling.

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  We prepared Co/(Pd-Au) multilayers onto a glass substrates by rf magnetron sputtering at room temperature. Co/(Pd-Au) multilayers exhibit a magnetic easy axis perpendicular to the film plane up to a larger magnetic layer thickness than Co/Pd multilayer. Especially, Co/(Pd_0.70Au_0.30) multilayers became perpendicular at 33Å. The magnetic anisotropy can be explained by the strain effect. The role of magnetoelastic energy due to the in-plane strain in the system is pointed out and discussed. We also investigated the magneto-optical(MO) polar Kerr effect of these multilayers. The polar Kerr rotation angle qk increases when the Au concentration is 4.5at% compared to Co/Pd multilayers, but decreases with increasing Au content.

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  In this paper we report on the preparation of sputter deposited Co/Pt multilayer thin films and the study of magnetisation reversal mechanisms in these films which are potential magneto-optic media. We have examined these mechanisms using well established bulk magnetic measurement techniques. Reverse domain nucleation and domain wall pinning controlled materials have been identified. We relate reversal mechanisms, including a bimodal process, to the hysteresis loops in terms of a two coercivity model. We have analysed the reversal processes using irreversible susceptibility curves obtained from measurements of remanence curves, and ΔM curves that reveal the effects of interaction mechanisms on reversal. We observe that close to saturation the samples exhibit weakly positive values of ΔM that indicate that the magnetised state is supported even though only domain wall processes are present. We also report experimental values obtained for coercivity, saturation fields, reverse domain nucleation and reverse domain wall critical fields. We explain deviations between values of the domain wall critical field obtained from isothermal remanent magnetisation and DC demagnetisation measurements in terms of the width of the domain wall energy barrier distribution. We identify a correlation between the values for these fields, and hence the reversal mechanisms exhibited by particular samples, and the structure of the films.

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  Magneto-optic measurements of the anisotropy [5] of multilayer DyFe films of constant composition, as a function of Dy layer thickness, confirms a maximum in perpendicular anisotropy for films containing monolayers of Dy. The results are discussed briefly in terms of available models for the origin of anisotropy in multilayers [6] and thin RE/TM films with non-S-state RE atoms [9].

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  Using the FLAPW method, electronic structure and magnetism of Fe/Al(001)/Fe are investigated. Spin and orbital magnetic moments of the Fe layer are 2.23 and 0.107 μ_B, respectively. The MCD spectra and band structures are discussed. Quantum well states are found at the Fe-Al interface.

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  Polar Kerr spectra of CoNi/Pt and Co/Pt multilayers were measured using a Kerr spectrometer. The polar Kerr sensitive depth (PKSD) is determined to be about 50 nm. When the film is thinner than this depth, the effects of beam reflection from the substrate can be observed in the Kerr spectrum. This is confirmed by measured and calculated results. The dependence of the Kerr spectra on the number of bilayers and individual layer thickness is investigated with regard to PKSD.

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  High precision, in-situ measurements of the magneto-optical polar Kerr rotation have been made continuously during the deposition of a series of Co and Pt multiple layers deposited by d.c. magnetron sputtering. Induced inhomogeneous magnetic moments in the Pt have been clearly observed and shown to fit very well to an exponentially decaying spatial function. The measured variations of Kerr rotation throughout the deposition of the Co and Pt layers can be simulated by classical electromagnetic theory using the optical and magneto-optical constants for Co and Pt. The latter are deduced from independent ex-situ measurements on several Co/Pt multilayers,

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  Magnetooptic recordings using the Near-Field Solid Immersion Lens (SIL) technique are analyzed by Magnetic Force Microscopy (MFM). The marks are found to be very regular and have sharp edges which is essentially important for mark-edge recordng. It is possible to measure both CNR and jitter from the MFM images of the high density, submicron size recordings. Due to high resolution of MFM these parameters represent potential recording properties. The CNR, jitter and qualitative analysis show that the smallest mark-to-mark spacing useful for recording is ∼120% of the isolated mark size. For the smallest marks this translates into a density larger than 2×10⁹ marks/inch². Results obtained show that the MFM can be used as a high resolution read-out technique for high density magnetooptic recordings.

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  We observed the shape and size of marks recorded magneto-optically on TbFeCo film, using spin-polarized scanning electron microscopy (spin SEM). We studied the laser power dependency of the marks recorded on a land/groove substrate. When larger power was used, the land/groove border acted as a barrier to the propagation of the magnetization reversal, which confirms the advantage of using a land/groove substrate for high-density recording. We also looked at the film roughness dependency of the marks. We found that the magnetization reversal processes depend on the underlayer roughness, which is related to the irregularity of the mark shapes and the recording noise.

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  A comprehensive approach to Magneto-Optic (M-O) stability was undertaken in order to address the reliability concerns from a broad spectrum of user applications and expectations. By measuring the changes in performance characteristics, starting at manufacturing and ending with data archiving, the reliability of this form of data storage was evaluated. Stresses designed to simulate packaging, shipping, warehousing, and storage were included. Following this, the interchangability among drives and read/write temperatures was tested as well as the erase/write/read cyclability. Finally a temperature and relative humidity Eyring model was validated for previous experimentation and an enhanced model for archival life was introduced.

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  We have already proposed two types of integrated micro MO heads for Mini Disc and reported on their characteristics [1],[2],[3]. These heads are made by forming optical elements such as holograms and beam splitters in multiple parallel glass plates. The type 1 head is made by laminating a 44 μm thick half-wave plate as an azimuth rotator[1],[2]. On the other hand, the type 2 head includes, instead of a half-wave plate, a polarization beam splitter which has a sloping incident plane making an angle of 45 deg. to the incident plane of polarization [3]. In this paper, we report mainly on the detailed structure of the integrated MO head developed for the Mini Disc, the characteristics of each optical thin film for the finite conjugate optical system used in this device, and the simulation results for a number of optical characteristics.

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  A new method for evaluating the readout channel of Pulsed Laser Irradiate Magnetic Field Modulation (PLIMFM) Magneto-Optical (MO) disks is proposed. Almost any form of signal quality degradation can be taken into account. Maximum Likelihood (ML) signal processing can significantly decrease signal detection error rates, especially when residual marks exist.

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  The requirements for optical tapes in an optical tape recording system using a rotating optical head are presented. Along with the requirements, the best structure for a magnet-optical (MO) tape was studied. As a result, a tri-layer structure was adopted for easy production and the tri-layerd MO tapes were experimentally fabricated. Performances and problems of an MO tape were experimentally investigated using these samples. And, the following results were obtained which realized performances equal to an optical disk using a thin polyethylene terephthalate (PET) substrate. (1) The incidence of the laser is from the tri-layer side to avoid the birefringence of the PET substrate. (2) Surface roughness of the PET substrate is below Ra = 7 nm. (3) Heat-resistance of PET substrate makes recording or erasing operations in excess of ten thousand times possible. (4) MO tape (width: 1/2 inch, thickness: 10 μm) was stable in terms of optical and magnetic properties under a tape tension of 0.5 kgw. (5) Sufficient tape tension is necessary to satisfy the requirement of flatness since MO tape has a large extent of curling.

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  CoFe₂O₄ and Co_1.80Mn_0.15Fe_1.05O₄ spinels were prepared as thin films. The as-deposited films were crystallized by conventional treatment (CT) and by rapid thermal annealing (RTA). The magneto-optical (MO) properties of oxides films were studied in relation with their thermal history. Between 600 and 800 nm the Faraday effect of RTA samples were different from those of CT films because the RTA process modified the cationic distribution of oxides and particularly the distribution of Co²⁺ ions on the sites of the spinel structure. We put the structural changes to advantage in order to optimize the MO properties of Mn-Fe cobaltites at 690 nm.

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  Ba and Sr hexaferrite films with perpendicular magnetic anisotropy were deposited on YSZ (100) and Si (100) substrates. Films on YSZ were highly oriented and grew by a spiral mechanism similar to that observed for growth on sapphire (0001). An obstacle to oriented growth on Si was its amorphous surface oxide. Substantial improvement in the texturing of the films was achieved by removing the Si oxide prior to deposition and carrying out the initial stage of growth in a reduced oxygen atmosphere.

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  Oriented, highly Bi substituted Dy iron garnet films with perpendicular magnetic anisotropy have been grown by pulsed laser deposition on (111) Ga₃Gd₅O₁₂, single crystal substrates, The effect of substrate temperature and oxygen pressure on the structure and magneto-optical properties of the films has been investigated. The Bi stoichiometry was found to be sensitive to both substrate temperature and oxygen pressure. The results suggest that at elevated temperatures required to nucleate the garnet phase, the oxygen background pressure must be sufficiently high to incorporate the volatile Bi atoms into the film. Reduced oxygen pressures negatively affect the perpendicular anisotropy.

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  The fundamental optical and magneto-optical constants of multilayered films of Co/Pt, prepared by balanced de magnetron sputtering, have been determined using ex-situ ellipsometry and Kerr polarimetry in the spectral range 300-900 nm. These parameters have been used to design trilayer structures that enhance the normal polar Kerr effect at short wavelengths. The design procedure is systematic and aims to maximise Kerr rotation, for a particular system reflectance, whilst at the same time keeping parasitic Kerr ellipticity zero. Trilayers based on the design glass/CoPt/SiO₂/Al, have been fabricated and their performance compared With theoretical predictions.

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  By using the "glycol gel process" utilizing nitrates of bismuth, yttrium and iron dissolved in ethylene glycol as the liquid precursor, single phase bismuth-substituted yttriulll iron garnet (Y₃-_xBi_xFe₅O₁₂) polycrystalline films with the amount of bismuth substitution x up to 2.5 were prepared by spin-on process on glass substrates, where garnet films with larger x were grown by repetitive gel-coating on thin garnet layer with x=1.5. In addition, the effect of copper or zinc ion substitution on magnetic and magneto-optical properties was examined for films with the chemical formula of Y₂BiFe_5-yM_yO₁₂, where M=Cu²⁺. or Zn²⁺

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  Thin layers of cobalt and Co/ZnO muitilayers have been deposited by metal-organic chemical vapour deposition and characterized by a range of structural and magnetic techniques. In general, the samples exhibited an overall in-plane magnetic anisotropy, the strength of which decreased with decreasing cobalt layer thickness. A buffer layer of ZnO was found to decrease the strength of the anisotropy with respect to a film of the same thickness deposited onto glass.

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  Thin films of Tb-Fe-Co have been annealed using a pulsed Nd:YAG laser in an attempt to investigate the effects of this on the magnetic and magneto-optic properties of the material. Results imply that as the laser energy density is increased the hysteresis characteristics of the film are changed due to an oxidation zone increasing in thickness. This has the added effect of reducing the energy associated with magnetic domain formation.

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  The depaendence of surface motphology of thin film garnets deposited by metallo-organic decomposition (MOD) on process conditions was investigated in an effort to produce MOD garnets with small roughness. The surface morphology of sputtered films were also studied for comparison. The surface morphologies were studied by atomic force microscopy (AFM) and cross-sectional electron microscopy. It was found that the surface morphology of the MOD films was very sensitive to film deposition conditions such as the number of layers, spincoating speed, heat treatment conditions, and the condition of the organic solution. It was also found that the MOD garnets were inherently rough due to a significant volume change which occurs during the drying and decomposition process. The smoothest MOD film showed mean roughness of order of 5 nm at 150 nm thickness while the roughness of the sputtered film was order of 0.5 nm.

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  The development of nonlinear optical microscopy based on Magnetization induced Second Harmonic Generation is demonstrated with magnetic garnet films taken as an example. A nontrivial modulated domain structure is shown to exist in a (210) oriented film, along with the possibility to study the magnetization component in the film plane directly and with a strong contrast.

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  Domain sizes in demagnetized samples are reported for polycrystalline films of thickness down to 30 nm and for thin single crystal weges of pure and Co/Ti doped BaM hexaferrites. The results compare well with domain theory which is amended by taking into account results of micromagnetic computations.

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  Recently reported magnetooptic diffraction theory adapted to analysis of planar structures is employed in simulation of the Kerr effect from micromagnetic model structures of fine (135 nm) stripe domains matched to experimental domain sizes in Co/Pd multilayers. Diffracted light propagation through a variable dielectric overlayer and an air gap into a high-index medium allowing propagation of the highly divergent beams is simulated with possible implications for scanning experiments.

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  In this paper, an approach to characterizing the shape of recorded bits is presented. This approach uses parametric Fourier descriptors (FDs). Some of the properties of FDs are discussed, and it is shown how FDs can be used to formulate a useful measure for shape irregularity, which is related to Signal to Noise ratio. Finally, it is shown that such a measure can be applied to characterize the shape of magneto-optically written bits, measured using MFM.

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  Monte Carlo simulations on a two-dimensional lattice of magnetic dipoles have been performed to investigate the rate of thermo-activated domain growth under a constant external field in thin magneto-optic films. The model considers two distinct energy barriers for domain nucleation and domain growth respectively. The nanoscale features in the domain wall motion are ignored. It is shown that during the growth process, the rate slows gradually as a result of the reduction in strength of the demagnetizing field and also may exhibit significant fluctuations if the domain structure is dendritic. For fixed domain size, the dependence on the applied field is found to be exponential v = v_oe^H/Ho, in agreement with experimental observation. The simulations also provide information on the demagnetizing and domain wall energy averaged over the domain boundary surface.

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  The method for measuring ∼ 1μm spot size at the moment when an optical disk is recorded or is reproduced is presented. The spot size is measured with scanning knife-edge method, and the edge of the aperture formed on a disk is used as a knife-edge. Two dimensional spot sizes are measured by using some angled apertures.

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  A technique is reported for accessing the absorptive component of magneto-optic interactions. Photo-acoustic detection is used to record hysteresis loops more usually obtained by monitoring changes in the reflectivity of samples as the magnetization is reversed. The sensitivity of the technique and its application is discussed.

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  A proposal for a novel detection system is presented for the readout of a ROM optical disc. The sytem has been developed for fast access by reducing the mass of the moving head to that of a lens array used for both focus and tracking. The detection system uses a position sensitive detector array specifically developed for this application. The fabrication of tile devices is described and the linearity plots of two types of devices are given. Results of current devices show an almost 100% linearity for p-type devices with zero cross-talk between channels. However, the n-type devices show approximately 70% linearity with very poor crosstalk. It is expected that alternative n-type devices using 100 micron trenching and wafer bonding will eliminate crosstalk making these devices a viable proposition for detection methods.

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  Coupling between diffraction gratings and magneto-optics can provide a non-conventional means of observation of a domain structure as shown by magnetic patterns typically sized near to the wavelength λ.
In the case of a simple unidimensional binary relief grating, diffraction can reveal surprising magneto-optical reemission properties. Modelling the behaviour of such an object gives quite satisfying results in the framework of a perturbative approach of the Rayleigh theory.
In the present paper we analyse any interesting features (Littrow mounting for diffracted orders, enhancement of magneto-optical signal for various orders) concerning the magneto-optical part of the diffracted light for a transverse Kerr effect configuration.
When the grating is made of soft magnetic lines deposited on a non magnetic substrate, diffraction measurements and studies give additional statistical informations about the collective magnetic behaviour. A model based on the average magnetisation distribution and the scalar theory of diffraction allows to plot hysteresis loops in good agreement with the experimental ones.

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  Thin layer magnetic fluids and films obtained after base liquid evaporation have been studied taking into account their interaction with a laser beam characterized by 632.8 nm wavelength and a magneticfield having a variable intensity up to 180 kA/m and 300 kA/m respectively .The dependence of the absortion coefficient on the magnetic field intensity H has been measured for both types of samples. Some experimental data are given in this paper. Results obtained after base liquid evaporation are discussed especially.

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  We present in this paper the effect of "oxidized-Si" surface layers of Si substrate en the optical, and magneto-optic properties of e-beam deposited Pd/(Pt/Co/Pt) modulated multilayer films. Large oscillations in the polar Kerr-rotation angk, θ_K, over the wavelength range 400 to 900 nm are observed in these films. In films deposited on substrates other than oxidized-Si, we do not observe such oscillations. The optical reflectivity of the multilayers is also found to oscillate in wavelength and the minima of the reflectivity occurs at wavelengths corresponding to the maximum Kerr rotation. This indicates that optical interference is the origin of the Kerrrotation oscillations. Refractive indices vs. wavelength measurements reveal that the oscillations in θ_K values originate from an optical interference at the surface SiO₂ layer of the Si substrate. Large θ_K's of 0.41° and 0.32° at about 400 and 800 nm respectively, and quite ideal square Kerr hysteresis loops are obtained in Pd-6Å(Pt-2Å/Co3Å/Pt-2Å) multilayer film deposited at 350°C with 100 Å Al buffer layers on oxidized-Si substrate.

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  The change in microstructure in sputtered CoNi/Pt Multilayers is studied as a function of the argon pressure. It is shown that as the sputter gas pressure increases the average grain size approximately stays constant, but the grains become more separated, the argon content decreases and the films tend to grow with rougher interfaces. Furthermore the increase in argon pressure also seems to lead to an increase in interface anisotropy.

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  Testing systems and method for estimating dust adhesion characteristics are proposed. Cartridges are exposed to heavy concentration atmosphere of dust particles under the condition that the disks rotate and the shutters are opened. Before and after the exposure, byte error rates (BERs) and reflectivity of them are measured. Fifteen kinds of 90 mm magneto-optical disk cartridges from eleven makers on a laboratory level and one kind of commercial cartridge were tested. The other cartridges were exposed to the authors' laboratory environment, air cleanliness of which met class 1,000,000, for two thousand hours. Two commercial cartridges were exposed for about two years without BERs of them increasing. It was also confirmed that the disks used for testing regained initial states of BERs and reflectivity by cleaning.

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  We have picked up the items for evaluating reliability of the Optical Disk Cartridge Case, and studied the test method for the respective items. In particular, we evaluated reliability of the cartridge case made of ABS resin with which a major reduction of material cost and molding cost can be expected.

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  We have proposed the standard test method regarding the optical disk life. We analyzed factors determining life, studied the life measuring method in relation to degrading of the recording film due to thermal diffusion at high temperatures, in particular, and showed the procedure.

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  The temperature of recording layer during read-out was calculated for some quadrilayer magneto-optical disks and the relation of carrier-to-noise ratio with figure of merit at this temperature was investigated at the wavelength of 532 nm. There have been found that the recording layer temperature has been more influential to carrier-to-noise ratio than the figure of merit, which indicates that temperature has other effects on CNR than reducing Kerr rotation angle and Kerr ellipticity. Practically, the recoding layer temperature can be adopted as a key parameter in improving carrier-to-noise ratio and we have got CNR of 49.1 dB at the wavelength of 532 nm.

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  The magnetic and magneto-optical properties of ordered Mn_1-xFe_xPt₃ alloy (0≤x≤0.45) films were investigated. The films were prepared by annealing Mn_1-xFe_x/Pt multilayers at a temperature of 800°C. The MnPt₃ alloy films was found to exhibit very large magneto-optical Kerr rotation, which reaches a maximum value of -1.2 deg at 1.24 eV. From the spectra of the off-diagonal component of conductivity tensor together with the diagonal component of dielectric tensor, it is suggested that the large Kerr rotation is due not to the plasma resonance but to strong interband transitions. MnPt₃/Co multilayer films were also prepared by MBE, and found to exhibit perpendicular magnetic anisotropy induced by the multilayered structure.

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  MnBi thin films with Al and Pt interlayers have been prepared by a sequential technique. Structural, magnetic, and magneto-optic properties at room temperature are discussed. We find that surface roughness intensifies with increasing film thickness due to the growth condition of Mn on Bi. Surface roughness is efficiently reduced by adding a thin Al or Pt interlayer. The coercivity strongly depends on adding interlayers or a protective overlayer. If the additional layer forms a rigid barrier, the MnBi formation is restricted perpendicular to the film surface, leading to a pronounced lateral growth and lower coercive fields. This could be related to an increase of 2.3% in volume between a stoichiometric Bi/Mn bilayer and the MnBi compound. The addition of Al interlayers does not reduce the Kerr effect considerably while a Pt interlayer reduces magnetization and, consequently, the Kerr effect.

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  Large Faraday rotations are reported tor Rh⁴⁺-substituted magnetic garnets in the visible wavelength region, in comparison with those observed in Ir⁴⁺ substituted ones. Although rather strong absorptions are observed in the visible region, no absorption peaks corresponding to the Faraday rotation peaks are observed in the absorption spectra. In order to study the origin of the Faraday rotations, Rh⁴⁺-and Ir⁴⁺-substituted nonmagnetic garnet films are prepared by an LPE method and optical absorption spectra are measured. In addition, the electronic state calculation of (M⁴⁺O₆^2-)^8- (M=Rh,Ir) octahedral clusters are performed by using the SCF-Unrestricted -SW Xα method. From the observed absorption spectra in nonmagnetic garnets and the electronic state calculations, large Faraday rotations are assigned to the charge transfer transitions of an electron from O 2p to Rh 4d or Ir 5d orbitals, or t_1uⁿ → t_2g^* and t_2uⁿ → t_2g^* transitions.

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  The stability of small recorded domain were investigated by the wall pinning force (Hw) which were calculated from the measurement result of wall expanding and shrinking coercive forces (He, Hs). He and Hs decrease with decreasing recorded domain diameter. Therefore Hw also decrease with decreasing recorded domain size. This result indicates that the writing stability of small domain ( < 0.4μmφ ) becomes low. The stability for recording 0.25μm domain on a RE-rich TbFeCo disk is higher than that of TM-rich one. It is found that the reason is originated from the large value of the Hw for the RE-rich TbFeCo at around recording temperature comparing for the TM-rich one by using the Huth model.

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  We have prepared Co_XNi_1-X/Au multilayers by evaporation and studied their magnetic properties and magneto-optical Kerr spectra. With the addition of Co the surface anisotropy increases linearly and stabilises the perpendicular magnetisation. For x= 0.7 the sample with magnetic layer thickness of 5.4 Å shows a rectangular loop with a maximum coercivity of 800 Oe. For thinner Co-Ni layers the Kerr peak due to the interband transitions of Au is clearly seen but for thicker layers it is the Co-Ni like behaviour. The spectra could be well explained by the electromagnetic model.

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