The temperature and field dependence of the complex polar Kerr effect and the optical reflectivity of CeSb single crystals are presented. The evolution of the magneto-optical effect to reach the new record value of 90 degree single Kerr rotation at 1.5 K and 5 T in the near infrared spectral range is discussed and qualitative arguments to account for this giant effect are given.

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  Progress in Magnetically induced SuperResolution since first reported in 1991 is reviewed. Recording on the disk by front aperture detection (FAD) was achieved for a bit length of 0.27 μm both by light intensity modulation and by magnetic field modulation. Since rear aperture detection (RAD) has the advantage of reducing crosstalk, the RAD type has the promise of realizing the huge capacity MO disk. RAD by a small initializing field and RAD by magneto-static coupling are expected to allow track pitches as narrow as 0.7 μm and bit lengths the same as achieved by FAD.

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  Nonlinear Optical (Second harmonic) reflectivity of magnetic surfaces gives rise to Magneto-Optical effects that are orders of magnitude larger than their linear equivalents. Together with its intrinsic interface sensitivity, this new technique appears to be very suitable for the study of magnetic thin films and multilayers and may lead to a novel way of Nonlinear Magneto-Optical imaging.

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  Results of an electronic theory for the nonlinear optical response at metallic interfaces are presented. It is shown that nonlinear Kerr-spectra reveal sensitively the atomic, electronic and magnetic structure. The nonlinear Kerr-rotation is generally much larger than the linear one and depends characteristically on the polarization of the incoming light. Thus, magnetic reorientation transitions can be easily detected as well as domain structures and magnetic structures of multilayer films. The second-harmonic-generation (S.H.G.) is polarization dependent, characteristically different for simple metals and transition-metals, and its temperature dependence can be used to study systems not at equilibrium.

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  We report results on a second harmonic generation study of thin films of magnetic garnets grown on (111), (210), (001), and (110) substrates. Experimental data on the rotational anisotropy of the SHG ID magnetic fields are well described using simple assumptions about the symmetry of these magnetic films.

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  The nonlinear magneto-optical Kerr effect on a Fe(110) surface and its dependence on the oxygen exposure is investigated at a wavelength of the incident light of 790 nm for different geometries. Especially for the transverse Kerr geometry a large intensity change upon reversal of the magnetization direction by a factor more than 4 is observed which can be increased to 80 by oxygen exposure. The magnetization induced part of the nonlinear susceptibility tensor is comparable in size to the nonmagnetic part.

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  Superlattices consisting of Fe and Au ultrathin layers with thickness of a few monolayers were prepared. Formation of L1₀-type structure in the Fe(1ML)/Au(1ML) superlattice was confirmed by X-ray diffraction. Magneto-optical studies suggest formation of a new energy band structure characteristic of the new alloy.

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  Magneto-optical (MO) polar and longitudinal Kerr effect spectra between 1.5 and 5.7 eV measured on series of magnetic multilayers Fe/Ag, Fe/AlN, Fe/Bi, Fe/V, Fe/Ta, Fe/Pt and TbFe/Pt with a varied thickness of ultrathin Fe are reported. The observed trends in the MO spectra can be explained using a 4×4 matrix model assuming the composition profile which incorporates interface transition layers. The aim of the paper is to demonstrate the effect of non-ferromagnetic spacer on MO spectra and to provide MO data for Fe suitable for the modeling of the optical interactions in Fe containing multilayers.

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  The present status of theoretical understanding of the magneto-optical Ken effect (MOKE) is reviewed. The theoretical research on MOKE has emerged from its initial stage, in which elementary ferromagnetic materials, like Fe and Ni, could be described, to a powerful first-principles electronic structure theory with which directly ‘materials engineering’ can be made. To illustrate this, we investigate the MOKE spectra of the following materials, which were selected because of their relevance for magneto-optical (MO) recording applications: (a) MnBi and derived compounds, (b) the natural layer systems FePt, CoPd, and CoPt, and related multilayers, (c) XPt₃ compounds with X=V, Cr, Mn, Fe, and Co, (d) ternary compounds related to PtMnSb, and (e) GdFe₂. The ab initio calculated MOKE spectra are compared to experimental spectra, if available. We predict several materials that could be promising for MO recording. We also propose a set of guidelines for the future predictions of materials having suitable MO properties.

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  The optimisation of sputtered CoNi/Pt multilayers for thermomagnetic writing has been studied with relation to the layer thickness, film structures and sputtering conditions. It was found that the writing was more easily performed in CoNi/Pt multilayers than Co/Pt multilayers because of lower Curie temperature in CoNi/Pt multilayers. The films deposited at a lower Ar pressure displayed sharp magnetisation reversal that results in the sharp domain boundaries around the written domains. The films deposited at a higher Ar pressure showed the undesirable microstructures and unsuitable magnetic properties which result in the worse written domains. The large perpendicular coercivity obtained in the film deposited at higher Ar pressure is attributed to the large voids in the film.

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  Three-dimensional Boundary Element Method (BEM) analysis of noise characteristics has been done to determine a suitable reproduction method for land/groove recording of magneto-optical disks. This analysis shows that groove depth fluctuation noise is much larger than groove width fluctuation noise or groove shape fluctuation noise. Noise in TM-polarization was also found to be lower than that in TE-polarization under calculation conditions which closely replicated practical disk conditions. The calculation results obtained agree well with experimental results. Finally, we propose a suitable reproduction method and substrate for use in magneto-optical disk land/groove recording.

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  We developed a new technology for writing and reading a tape which shows good perspectives for very high track density recording. The key elements of this new technology are:
  - parallel recording of a large number of tracks thanks to a matrix head structure creates macro tracks which are significantly wider than the guardband separating adjacent macrotracks,
  - optical detection of the magnetic flux flowing in the reading core thanks to Kerr effect allows high transverse resolution and precise track following,
  - parallel readout of adjacents bits allows efficient electronic crosstalk compensation,
  - serpentine structure, allows recording of a very large number of tracks on wide tape without requiring stringent precision on tape stability and mechanical positioning.

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  For high density MO recording, a new recording method, magnetic multi-valued MO (MMV) has been introduced[1]. A quadri-valued recording was realized using a magnetic field modulation method. For practical use of this technique, the external field for recording four levels has been reduced down to 150 Oe arranging magnetic capping layer composition of the MMV media. And using the laser pumped field modulation recording method, 0.8μm mark recording has been achieved on the quadri-valued media, which effectively corresponds to 0.4μm binary mark recording.

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  We propose a new multi wavelengths read-out method which solves the fatal problem of decreasing the signal to noise ratio (SNR) in multi-valued magneto-optical (MO) recording. Theory and method to find the optimal condition are discussed and the two examples for the disks of RE-TM films and the combination of RE-TM and magnetic garnet films are investigated. This method provides theoretically 12.5 dB higher SNR than conventional one, and is suitable to realize 3-dimensional MO recording with the combination of the multi-valued MO recording proposed by Ohta and Shimazaki et al.^[1]

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  We present a potential to achieve an ultrahigh density recording in both a nano-bit writing and a high speed readout using an evanescent light-phase change recording. As a result, we first demonstrate a 60nm-diameter phase-changed domain (bit) writing, which means the possibility to achieve an ultrahigh density recording of 170Gb/in².The possibility to read the phase changed bits at a high speed of 10Mb/s is discussed.

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  SNR of a polycarbonate MO disk with a narrow track of 0.85 μm and with a quadrilayer structure was improved by optimizing and improving the groove geometry, film composition / thickness, and birefringence of the substrate. By using a 690 nm LD, an NA of 0.55, magnetic field modulation, and RLL(1,7) coding, a high areal recording density of 2.5 Gbit/in² was obtained. Moreover, the PRML detection of PR(1,2,1) increased the density up to 2.9 Gbit/in².

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  Advances in optical recording technology enabled DVD to achieve a disk capacity of 4.7 GB per side, a major improvement over CD media. We summarize tile key techniques used in DVD to achieve this remarkable accomplishment, and examine the implication of these techniques for MO recording channel and disk format.

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  Land/groove recording properties on a magnetically induced super-resolution (MSR) disk has been investigated. We prepared an exchange coupled type of MSR disk with double magnetic layers and examined the read/write characterisitics for various track pitches with magnetic field modulation recording. As the results, a track pitch of 0.65 μm was available for practical use from the point of view on crosstalk and crosswrite properties. We have also developed a new groove format in order to obtain address information on both lands and grooves.

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  We have proposed magnetically induced super resolution (MSR) media consisting of three magnetic layers with in-plane magnetization films (T-MSR). T-MSR realize high MSR performance without readout bias magnetic field. Of two types of T-MSR, exchange-coupled media is suitable for stable readout than magnetostatic-coupled media. The recording density and data transfer rate are estimated to be 3.5 Gbit/inch² and 6 MByte/se, respectively using a optical head with wavelength of 680nm and numerical aperture of 0.55.

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  This paper describes the MSR method for high density recording. A series of tests was conducted using magnetic field modulation combined with a laser pulse. A slider embedded with a tiny permanent magnet was developed as an initializing magnetic head. A 680 nm wavelength laser and a 0.55 NA magneto-optical head were used for recording and reading. A MSR disk is made suitable for use combining of NRZi modulation and magnetic field modulation. Using the above, we confirmed the practicality of the MSR disk at a minimum mark length of 0.2μm (0.2μm/bit).

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  The phenomenon of the total internal reflection of light from the interface of bigyrotropic magnetic media is theoretically considered. Analytical expressions for the critical angles for an interface of two cubic bigyrotropic media are obtained. Numerical calculations for the interface of bigyrotropic yttrium-iron garnet and nongyrotropic gadolinium-gallium garnet are made.

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  Optical reflection and the polar Kerr rotation of four single crystals of barium hexagonal ferrites were measured in the visible and near infrared region at room temperature. Local extrema of the polar Kerr rotation at wavelengths of 1650, 1350 and 760 nm could be assigned to the presence of Co²⁺ in tetrahedral positions. The figure of merit attains the maximum values at these wavelengths suggesting material to be suitable for the magneto-optical storage applications.

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  A combined investigation of the magnetization, Faraday rotation, polar Kerr rotation and the X-ray photoelectron spectroscopy of two Co- and Ti-substituted hexagonal ferrite films, prepared by pulsed laser ablation deposition, was made. The investigation indicates the presence of a certain amount of three valent cobalt ions within the majority of two valent cobalt states.

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  In this work, we have studied the magneto-optical (MO) and the dynamic behavour of exchanged-coupled (EC) layers between the Nd16Tb14Fe52Co18 (at. %) films for the read-out (RO) layers and the Tb22Fe70Co8 (at. %) films for the storage (ST) layers. In the five layered SiNx/NdTbFeCo/TbFeCo/SiNx/Al-Ti films, the Kerr rotation angles (θk) increased compared to those of the four layered films with either a mono-RO or a mono-ST layer at R (thickness ratio of ST to RO)≤3. The coercivity (Hc) significantly increased from 1.19 KOe-2.77 KOe to 2 KOe-5.6 KOe in an entire range of R. This was ascribed to an occurrence of the exchange-coupling between RO and ST layer. Squareness ratio monotonously increased from 0.75 to 1.0 as R increased from 1.5 to 6. The maximum carrier-to-noise ratio (CNR) of the five layered magneto-optical disk enhanced from 36.5 dB to 47.6 dB as R increased from 1.5 to 6. This was attributed to the improved Hc and the enhanced squareness due to the exchange-coupling. The composite of the experimental results suggests that thinner RO layer is favorable to obtain the high MO properties and the improved dynamic characteristics.

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  Multilayered systems with magnetooptical films find wide applications in integrated optics and optoelectronics, generally. In this paper optical properties of three-layered systems are discussed. Attention is paid to waveguiding in the system of a single ultrathin magnetic layer (Ni, Fe, Co) buried in isotropic dielectric medium (AlN). The influence of geometrical parameters of layers on dispersion relations is derived.

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  The nonlinear magneto-optical response of a magnetic metal as a function of the thickness of a noble metal overlayer shows that an oscillatory behavior dominates the total generated second harmonic output. The oscillation periods are approximately twice as large than those observed with linear Kerr effect measurements or estimated from the Fermi surface. The spectral dependence of the signal indicates that the thickness independent background is due to interband transitions while the oscillatory part persists at lower photon energies.

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  We attempt to prepare the epitaxial Fe-Pt alloy films with a CuAu-type structure, which are expected to have a large magnetic perpendicular anisotropy. Epitaxial growth is attained for the films with nearly equi-atomic composition by making use of MgO (100) substrates and Pt buffer layers. Good rectangular loops of polar Kerr hysteresis are obtained for the prepared films with 51-56 at.% Fe. The results of conversion electron Mössbauer spectroscopy (CEMS) reveal that the domains where the c-axis of the crystal is parallel to the film plane grow gradually, as Fe concentration increases and also the precipitation of paramagnetic γ-phase Fe occurs.

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  A short review of publications devoted to theoretical and experimental investigations of nonlinear optical effects in magnetic crystals is presented.

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  We have performed room temperature measurements of the polar Kerr effect on bulk samples of MnPt₃ and, for the first time, CrPt₃. The as-polished MnPt₃ and CrPt₃ samples show very weak Kerr signals which varied with the parameters of the polishing procedure. The etched samples show orders of magnitude larger Kerr signals with a typical dispersive-like photon-energy dependence. For MnPt₃ we observe a maximum Kerr rotation of 0.55°C, which is a factor of 3 smaller than prediced by theory. For CrPt₃, a Kerr rotation of 0.35°C is observed, which is a factor of 2.5 smaller than predicted by theory.

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  Magneto-optical Faraday effect of cobalt nano-clusters oriented uniaxially in a transparent matrix was studied. The experimental results showed that the oriented films were good polarizing plates with very unique MO properties which varied depending on the geometry of film structures and the polarization of incident lights. Numerical analysis revealed that the MO properties originated in the mode conversion of lights from TE to TM, arising from the magnetic and optical uniaxial anisotropies.

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  We have modified the Bruggeman's effective medium theory(EMT) to study the microstructural dependence of the magneto-optical spectra in magnetic materials having the off-diagonal elements of the dielectric tensor. We have applied this modified EMT to 20-Å-thick Co film having island structure and observed that this modified EMT exhibited better match to the experimental data than any other existing theories.

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  MnAs and MnSb thin films were grown on GaAs (100) substrates by hot-wall epitaxy (HWE) technique. Epitaxial growth with (10-11) axis parallel to GaAs (100) surface was observed in both films. Polar magneto-optical Kerr rotation and Kerr ellipticity spectra were measured in these samples. For MnAs, it is for the first time that reliable polar Kerr spectra were obtained.

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  Anisotropy dispersion of rare earth constituents, and canting between rare earth and transition metal subnetworks were used to explain the recording characteristics of (Dy,Tb)FeCo magneto-optical recording films. Through the quantitative measurements and mean field calculations of the exchange coupling coefficient λ, we have found that the higher λ is, the higher required bias field will be during recording. Therefore, the recording characteristics of ferrimagnetic and sperimagnetic films can be determined and further improved through careful characterization of λ of magneto-optical media.

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  At λ= 633 nm, very accurate measurements of the Faraday rotation on epitaxial garnet films of the composition {R_3-xBi_x}[Fe₂](Fe₃)O₁₂ with R = Dy, Y and high Bi content (x ≅ 1.30) are reported, in the temperature range 10 -620 K under magnetic field up to 20 kOe applied along the [111] direction. The analysis of the data in terms of the sublattice magnetization reveals, at low temperatures, a large contribution of the rare earth {c } sublattice induced by the Bi substitution. This enhancement of the "electric" dipole Faraday rotation is strongly temperature dependent and vanishes at room temperature. This result is compared with that observed for the same Bi-substituted rare earth iron garnets in the near infra-red band.

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  Amorphous NdTbFeCo alloys are prepared with different substrate positions and rotation speeds of substrate holder to investigate the effect of magnetic properties on Kerr rotation angle. Angular momentum of the substrate holder induces high squareness of magnetic hysteresis loops in the amorphous alloys. This leads to the fact that the magneto static energy of the hysteresis loops is proportional to remanent Kerr rotation angles.

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  RE/TM films used for magneto-optical (MO) data storage are commonly covered with reactively sputtered SiN protective layers. For stoichiometric Si₃N₄ cover layers no reaction between the magnetic and the protective layer is expected. But if there is a surplus of nitrogen within the protective layer the magnetic properties and the long-term stability of the magnetic layer may be influenced.
To investigate this we prepared ferrimagnetic TbFeCo-films covered with a SiN protective layer containing a surplus of nitrogen. For testing their long-term stability the films were annealed several times. To analyze the magnetic properties measurements of Kerr hysteresis were performed. The magnetic anisotropy was measured by Kerr Torque Magnetometry, a very sensitive magneto-optical method which provides local information about the anisotropy field at the surface region of the magnetic layer.
As a result substantial changes of the magnetic properties at the surface region of the TbFeCo layers were detected. These changes were induced by a diffusion of nitrogen from the protective into the magnetic layer leading to a reduced content of magnetically active Tb at the surface. At longer annealing times this led in extreme to a double layer behaviour which makes the medium useless for MO data storage.

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  Theoretical investigation of magnetization configurations and reversal processes is presented in exchange-coupled double layer (ECDL) and trilayer (ECTL) with mixed parallel and perpendicular anisotropy structures (F₁/F₂) and (F₂/F₁/F₂) where F₁ is a planar magnetization film corresponding to binary NdCo or ternary GdFeCo amorphous alloy and F₂ is a perpendicular magnetization film such as DyFeCo alloy. It is shown from the analytical study that the magnetic profiles are strongly dependent on the magnetic parameters of the layers F₁ and F₂, the films thickness and the external field along the normal to the film plane which gives the possibility to investigate the magnetization reversal in the multilayers. Calculations are derived in ECDL from a variational method of the magnetic energies in a continuous model and in ECTL from a noncontinuous model. The magnetization profiles and reversal processes are analyzed from an effective exchange induced inside the perpendicular layer F₂ by the capping planar layer F₁.

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  The magnetic, anisotropy, and the magneto-optic properties of (Co/V)_n multilayers prepared by e-beam evaporation under ultrahigh vacuum are presented. The magnetization at 5 K suggests one atomic layer of Co to be nonmagnetic. The overall magnetization is found to have a linear temperature dependence, which indicates a lowered dimensionality in these (Co/V)_n multilayers. The surface and bulk anisotropies constant are determined to be at room temperature, K_s = 0.5 erg.cm^-2 and K_v = 9.4 10⁶ erg.cm^-3, respectively. Polar Kerr rotation (PKR) dependence on t(Co) and t(V) are also presented. It is found that PKR decreases monotonicaly with increasing V thickness for the samples with t(Co) = 22.5 Å.

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  The temperature dependence of the magnetization processes in mixed exchange-coupled double layers ECDL with a planar GdFeCo film 1 and a perpendicular anisotropy DyFeCo film 2 is analyzed from Faraday rotation measurements. During heating the magnetic state of the ECDL presents strong modifications depending not only on the external field applied along the normal to the layers, but mainly on the ECDL type which can change from a type 1 with an interlayer macroscopic antiferromagnetic (AF) coupling -A₁₂M₁.M₂ to a type 2 with a ferromagnetic (F) coupling. From appropriate choice of the deposition parameters the films compositions were adjusted for either T_cp1<RT<T_cp2 or RT<T_cp2<T_cp1 where T_cp1,2 are the compensation temperatures of the layer 1 and 2 which gives the possibility to obtain at RT ECDL of type 1/AF or type 2/F respectively. Depending on the respective values of T_cp1 and T_cp2, it is observed by increasing the temperature, F→AF or AF→F type transitions at T_cp1 and T_cp2. The evolutions with the temperature of the magnetooptical (MO) hysteresis loops of the ECDL are explained at the first order from the parallel change of the individual loops of the layers 1 and 2. However very close to T_cp2 more complex MO loops are observed and can be explained from the rise of the hysteresis H_c1 in the planar layer 1 induced by a strong increase of the coercitivity H_c2 of the perpendicular layer 2 near its compensation temperature.

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  The coercivity mechanism in polycrystalline CoCrPt thin films, Co/Pt multilayer systems and in amorphous TbFeCo thin films was studied by analyzing the field and time dependencies of the magnetization. The initial susceptibility X₀ and the apparent coercivity as deduced from measuring minor loops indicate a much larger contribution of reversible magnetization processes and a much broader switching field distribution in the polycrystalline CoCrPt magnetic recording medium as compared to the perpendicular magneto-optic Co/Pt and TbFeCo media. The magnetic interactions in the media have been determined by δM measurements yielding the strongest interactions in the amorphous TbFeCo films and the smallest in the polycrystalline CoCrPt films. Analyzing the relaxation behavior of the magnetization the Barkhausen volume was estimated for all the three media and compared with the results from microstructure analysis by TEM and AFM.

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  We have investigated the growth and magnetic properties of ultrathin Fe films on Au(001). The films used for magnetometry have been prepared by MBE on pre-annealed MgO(001) single crystals. Epitaxial growth of the 300-500 monolayer Au buffer layer as well as of the Fe films in the monolayer range could be achieved by use of a Cr seed layer. Epitaxial quality and surface structure was controlled in situ by electron diffraction (LEED, RHEED) and ex situ by STM and AFM. Comparative growth studies were performed for Fe-films on a Au single crystal substrate by in situ STM and ion scattering spectroscopy. We have investigated the magnetic anisotropy of Fe films in the range 3-50 monolayers with alternating gradient magnetometry (AGM). We find a uniaxial out-of-plane contribution of the surface anisotropy which promotes a spontaneous out-of-plane magnetization for films < 2.1 monolayers. Additionally, we report on a fourfold in-plane surface anisotropy, which leads to a switching of the in-plane easy axes into the [110] and [-110] directions for the 3 and 5 monolayer Fe films. We discuss these anisotropy phenomena in context with the breaking of translational symmetry at the interface.

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  The phase-change optical disc is one of the most promising candidates for the next generation rewritable, optical discs. For multimedia and video applications, high capacity and high data-rate are required. The choice of the phase-change material, usually a Ge-Sb-Te compound, becomes extremely important since data rate is related to the minimum time for crystallization of the recording material. The availability of high-power, red laser diodes combined with an objective lens with high NA and the application of the mark-edge recording technique, offer the possibility to increase the storage density. We realized a capacity of 2.6 GByte continuous data on a pregrooved disc with a diameter of 12 cm. More than 10⁵ direct overwrite cycles at a bit rate of 18 Mbit/sec were achieved by optimizing the disc structure and recording strategy.

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  The recording properties of common single layer magneto-optical (MO) disks can be improved by introducing exchange coupled rare-earth (RE) transition-metal (TM) films, both from the point of view of capacity and data transfer rate. MO multilayer stacks must exhibit exchange coupling in order to be suitable for direct overwrite (DOW) and magnetic superresolution (MSR). Thin DOW stacks require an interface layer to adjust the exchange coupling. Soft magnetic Gd-Fe and Gd-FeCo interface layers exhibit suitable magnetic properties to meet the DOW demands. The best solution would be a RE-TM interface layer with inplane anisotropy at room temperature and perpendicular anisotropy at elevated temperatures. Such a layer can also be used as a read-out layer in MSR stacks. Therefore we studied the anisotropy of evaporated and sputtered Gd-TM films as a function of composition. Gd-FeCo films with a Co/(Fe+Co) ratio less than 0.47 showed a transition from inplane to perpendicular anisotropy with increasing temperature. The transition temperature T_trans depends on the Co/(Fe+Co) ratio and the Gd content and can be adjusted between 0 K and T_C. The temperature range ΔT_trans, where the magnetization direction changes from totally inplane to totally perpendicular, was 70 ± 25 K for all evaporated samples while it depends on Ar pressure for sputtered samples. Triple layer DOW disks showed a maximum CNR of 51.4dB.

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  Among many type of recording media MO storage has higher possibility to progress with improving random access speed and transfer rate, minimizing drive size, and high capacity at the same time. A lot of engineers have thought one of the approach for such improvement is light intensity modulation direct over write method (LIM-DOW). They thought, however, it was hard to mass-produce because LIM-DOW media consists of multiple magnetic multilayer. So we have been using quality engineering (Taguchi method) to improve the efficiency of development. And it was proved that it was possible to do the mass-production of LIM-DOW media.

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  We present, for the first time, the direct observation of the dynamic reading process in central aperture detection (CAD) magnetic super resolution (MSR) media. The stroboscopic images taken by a 10ns exposure time high speed Kerr microscope system on an airbearing spin stand are compared with the corresponding CNR measurements on a MO spin stand. Dynamics of the reading process in samples with and without an intermediate layer and at different reading conditions are studied. Our analysis indicates that the intermediate layer sharpens the threshold for copying the data into the readout layer. We find that optimizing the reading power in CAD MSR readout is critical in order to achieve fast copy speed and provide clear and complete copying. The optimal reading power increases with the increase of the linear velocity of the disk, as expected. Higher disk velocity results in a smaller thermal aperture, which is shifted further from the center ofthe optical aperture, resulting in a decrease in CNR.

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  The origin of the thermomagnetic writing of information bits in magnetooptical recording media is not completely solved. The formation of magnetic bubbles during or after the short time local heating of the medium by a focussed laser beam is not yet well understood. Precise time resolved measurements and corresponding calculations are still chalenging. The difficulty of the data analysis comes mainly because thermal and magnetic experimental length scales are of the order of the light wavelength. We present here coupled nanosecond time resolved measurements of the heat diffusion and of the writing process in a Tb/Fe multilayer with a compensation point below room temperature. This enables us to deduce the spatio-temporal variation of the temperature and to prove that the formation of the magnetic bubble occurs during the cooling of our sample. A good fit of our thermal data can only be obtained if the thermal conductivity of our magnetic multilayer is supposed to be more than one order of magnitude smaller than the bulk alloy conductivity.

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  Micromagnetic finite element calculations rigorously describe the effects of microstructural features on the magnetic properties of Co/Pt multilayer thin films. Within the framework of static micromagnetism, the hysteresis properties result from subsequent minimum energy solutions for decreasing or increasing applied fields. The concurrent modelling of inhomogeneous magnetic states within the individual grains and of co-operative reversal processes leads to a large-scale optimisation problem. In order to reduce the number of variables, shell elements which account for the multilayer structure and a magnetic vector potential to treat the long-range stray fields are used. Micromagnetic calculations of demagnetisation curves and domain structures in Co/Pt multilayer systems show a qualitative agreement with experimental data obtained from Lorentz electron microscopy. The nucleation field of Co/Pt multilayer increases with improving texture. Spatial fluctuations of the anisotropy directions from grain to grain create barriers for domain wall motion. The pinning field increases with increasing grain size. The coercive squareness improves with decreasing number of bilayers. The ac-demagnetised state shows a maze-like structure. The underlying skeleton shape of the domain structure remains substantially unchanged under an applied field. The transition width and the domain wall jaggedness increase with decreasing quality of texture and increasing grain size.

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  The storage media for the magneto-optic (MO) recording technology available on the market today consist of thin ferrimagnetic films of amorphous rare earth/transition metal (RE/TM) alloys. Because the writing speed is limited by the need to erase entire sectors before writing new data, great effort has been made to develop direct overwrite (DOW) techniques, where the light intensity modulation technique appears to be the most promising method. This technique involves the use of exchange coupled layer systems as storage media. On the other hand, exchange coupled layer systems can also be used to increase the storage density without changing the optical arrangement introducing the so called magnetically induced superresolution process (MSR). Both methods, however, suppose a detailed knowledge of the switching behaviour of the exchange coupled films.
Therefore, exchange coupled double layers (ECDLs) were produced and their magnetization reversal behaviour was analyzed yielding a characteristic switching field diagram for each investigated sample. Using this switching field diagram, a formalism was deduced, which enables to prove the DOW or MSR capability of exchange coupled layer systems using data only obtained from macroscopic investigations (Kerr measurements).

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  Land & groove recording on MO disk with modified optics and PA-MFM are investigated. Cross-talk cancellation by phase compensation is achieved and it is suppressed down to -30dB. DSB(Double Shading Band) enlarges the carrier level for short mark.

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  A comprehensive model for the readout process in magneto-optic replay is presented. Applications to areas of current interest, including Partial Response signaling and Pulse Width Modulation recording techniques, are discussed.

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