The evolution of magneto-optical recording technology as well as materials is reviewed. A bit density higher than 10⁸ [bit/cm²], which is about 3 times higher than that specified by ISO, has already been realized by employing ZCAV technique together with the mark edge recording. The density may attain a value of 10⁹ [bit/cm²] around the beginning of next century by the use of superresolution disk combined with shorter wavelength SHG laser. If it is possible to apply a near field scanning optical microscope method, a recording density of higher than 10¹⁰ [bit/cm²] could be expected. Accompanied by the progress in recording density, a remarkable down sizing for a definite capacity memory or huge capacity image. recorders for video have been realized. On the other hand, as for a task of higher speed required for random access computer memory, the footstep of recent development is not clear and the future is difficult to forecast.

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  Reflectivity spectra were measured between 0.5 and 25 eV using synchrotron radiation in Pt-based multilayers and alloys, for which magnetooptical (MO) spectra had been evaluated between 1 and 6 eV. Analyses using optical constants obtained from the reflectivity revealed that the MO spectra of multilayers can well be simulated assuming the presence of an alloy layer at each interface, the layer thickness being approximately 6-10 Å. The prominent MO structures around 5-6 eV commonly observed in both Pt-based alloys were ascribed to the plasma-edge enhancement effect.

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  We present two major aspects of magnetic anisotropies in Co-based multilayers. Within the framework of a continuum free energy calculation we show that the experimentally observed large uniaxial in-plane anisotropy in epitaxial single-crystal (110)-oriented Co/Pt and Co/Pd superlattices is caused by magnetoelastic interaction. From Brillouin light scattering experiments the lateral and layer-to-layer variations of anisotropies in Co/Pd- and Co/Au-multilayers are analyzed on the length scale of spin-wave excitations (≈ 3000Å), which is also a characteristic length scale for domain formation in magneto-optic recording.

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  The combination of a high resolution and essentially no sample preparation, makes magnetic force microscopy a powerful characterization technique for magnetic storage media. This is illustrated by images of domains recorded on GdTbFe and Co/Pt magneto-optical disks. Scanning force microscopy with magnetic as well as nonmagnetic tips has been used to obtain more insight into the effects of a mild sputter etch of the dielectric layer before the deposition of a Co/Pt multilayer. The main effect of the sputter etch is a reduced roughness of the multilayer which results in a lower disk noise.

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  Magneto-optical properties of the magnetic materials can be improved by constructing nano- or atomic-scale multilayers. A recent result on new magneto-optical transition in the Fe/Au(100) sandwiched films and multilayers shows one possibility to control the band structure of magnetic metals. In the case of 2 atomic layers of Fe(100) plane sandwiched by Au(100) layers, the off-diagonal part of the dielectric tensor shows an about 2 times increase at 4eV by the transitions between d-bands and p-quantum well states in the Fe ultrathin layer.

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  Mossbauer spectroscopy and magneto-optical (MO) studies of thin amorphous Tb_xFe_100-x films (11‹x‹34 at.%), subjected to the pulsed laser annealing, were carried out. The TbFe films (160 nm thick) were RF-sputtered onto glass substrates; both sides of the films were passivated with SiN layers (85 nm). Both Mossbauer and MO measurements confirmed that in the successively annealed films spontaneous magnetization is well aligned along the film surface. The evolutions of hyperfine field distribution at ⁵⁷Fe and MO data reveal that the laser annealing results in the atomic ordering of TbFe alloys. The crystalline phase of α-Fe appears in the Fe-rich films subjected to laser annealing.

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  We report a technique for producing the ordered PtFe intermetallic compounds with perpendicular magnetic anisotropy and a preferred c-axis orientation perpendicular to the film plane. These tetragonal alloys possess large magnetocrystalline anisotropy and magnetizations, suggesting them as candidates for magneto-optic and perpendicular magnetic recording.

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  Evaporated Co_xNi_(1-x)/Pt multilayers can be used as a medium for magneto-optical recording. For all Co-Ni ratios we prepared, perpendicular magnetization can be obtained, depending on the multilayer-structure. The anisotropic energy decreased for increasing Ni-amount in the alloy. The Curie temperature is lower than for the Co/Pt multilayers. Unfortenately also the H_c and θ_k decrease, but R/W measurements have shown that the optimum write power of a Co-Ni/Pt multilayer is significantly lower than for a Co/Pt multilayer with comparable H_c and θ_k.

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  This paper describes a method and results of in situ measurement of stress for Co/Pd multilayer films deposited by rf sputtering. An optical non-contact displacement detector is set at the behind of the substrate. The substrate is hold at one of the ends of the substrate and the detector is set at near the free end of substrate. Change of displacement (d) between the detector and the substrate caused by the bending of the substrate which corresponds to the stress in the film.
  For Co single film, stress is tensile and its value is almost constant with increasing film thickness, while in Pd single film, stress is also tensile at the beginning of the deposition and it takes a minimum value at near the 80 Å of Pd thickness and then it changes to compressive.
  For Co(4Å)/Pd(30Å) multilayer films deposited directly on the glass substrate, at very beginning of the deposition, the stress in Pd and Co layers are tensile and compressive, respectively. This distribution of stress is gradually changed with the progress of deposition. After the deposition of over 20 periods of Co/Pd, the stress in the Pd and Co layers are changed to compressive and tensile, respectively.

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  Large Kerr rotation angles with a perfect squareness of hysteresis were obtained in Co/Pt multilayers by constructing a modulated layer structure. The Co/Pt multilayers were prepared by sputtering onto a SiO₂ substrate. Multilayers with Pt interlayers showed large Kerr rotation angles up to 0.8 degree and stepwise hysteresis loops with a perfect squareness were also obtained. Optical calculation proved this Kerr enhancement to be due to optical interference and multiple reflection. Cu interlayers in the layer modulated multilayers substantially decreased the Kerr rotation. The authors have also found that very thin amorphous CoZrNb underlayer significantly improves coercivity.

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  This paper presents some results from an investigation of the magnetic, magneto-optic and optical properties of Co-Pt bilayers, multilayers, and designed phase optimised "trilayer" structures. Suitable magnetic properties are obtained in N(0.4nm Co-1.1nm Pt) multilayers with the period number, N, between 5 and 10. The magneto-optical and optical properties of the multilayers are found to be in good agreement with those calculated from an equivalent single layer model. Calculations of the spectral response of these properties over the range 300-900 nm for the designed trilayers are found to agree very well with measurements on fabricated glass/Pt/(Co-Pt)/SiO₂/Al structures.

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  We have prepared Tb₁₇Fe₈₃ /Pt multilayers by rf sputtering and studied their magnetic and magneto-optical properties. As the TbFe layer thickness decreases below 200Å, the magnetization increases, the rectangularity of the M-H loops and the coercivity decrease. These results are explained in terms of an interfacial Fe-Pt layer. Further more, the effective anisotropy which is strongly positive for TbFe layers 200 Å thick, decreases linearly with the TbFe layer thickness yielding a negative surface anisotropy Ks = -0.73 erg.cm ^-2. The torque curves also indicate a region with an in-plane magnetization. The polar Kerr rotation initially shows a sharp increase with a decrease in the TbFe layer thickness but reaches a saturation.

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  microstructure of amorphous TbFeCo metal alloy thin film is investigated by scanning tunneling microscopy. Morphology of TbFeCo film shows a cluster structure, nanocrystalline is observed presenting in this amorphous thin film, the size of nanocrystalline is 2∼3nm. Atomic resolution image of nanocrystalline, which is very diffcult to image in air by STM, is also shown in this paper. We regarded that the key to get atomic resolution image of metal material is preparation of large scale very smooth sample surfaces.

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  A wavelength dependent, quantitative comparison of the static magneto-optical signal in Co-Pt and Co-Pd alloys, Co/Pt and Co/Pd multilayers and TbFeCo has been carried out. Dynamic testing of evaporated Co-Pt and Co-Pd alloys, embedded in quadrilayer structures has been demonstrated at 488nm. Large mark CNR ratios above 60dB in Co-Pt alloys were found on ungrooved glass disks.

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  An x-ray diffraction study has been carried out to study vertical lattice strain in polycrystalline HV evaporated Co-Pt and Co-Pd alloys and UHV evaporated Co-Pt alloys on SiN buffered fused silica substrates. The data support an inhomogeneity model, which was proposed to explain the occurence of perpendicular magnetic anisotropy in these alloys. The effect of subatomic layering on magneto-optic properties in 100nm thick HV evaporated Co₂₈Pt₇₂ is reported.

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  Magneto-optical recording materials with high remanent Kerr rotation at short wavelengths were successfully obtained in a trilayer form. A NdFeCo amorphous film with in-plane magnetization, but with a large saturation Kerr rotation angle at short wavelengths, was sandwiched between TbFeCo amorphous films with strong perpendicular anisotropy and high coercivity. The trilayer film, Tb₂₀Fe₇₄Co₆ (10 nm)/Nd₁₆Fe₅₇Co₂₇ (7.5 nm)/Tb₂₀Fe₇₄Co₆ (100 nm), shows a remanent Kerr rotation angle θ_Kr = 0.32° at a wavelength of 400 nm, coercivity H_c = 2.4kOe, and a good square loop (θ_Kr/θ_Ks ∼ 1).

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  Extremely fine grains of high-Bi content garnet films are obtained by crystallizing the amorphous films deposited on low-Bi content underlayer garnet films. Proper selection of the lattice mismatch between the two layers gives a grain size of 40nm in the upper memory layer. Pseudo-dynamic writing test of this bilayer film shows that bits of 1μm in length can be recorded in a relatively good shape.

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  Series of Co/Pt and Co/pd multilayers have been prepared by RF sputtering (Leybold Z-400) using Ar and Kr as sputtering gas. In this case we used one target position on which two small targets were fixed. The background pressure was typically 1*10^-7 mbar. The substrates were positioned below the targets on a rotating table. The thickness was determined by measuring exposure time combined with Dektak and low angle x-ray measurements. The number of bi-layers is 25. The hysteresis loops were measured by VSM and MOKE tracer.
The effective anisotropy has been measured by Torque measurements and further characterisation has been made by low and high angle x-ray diffraction. All films have been prepared on Si (100) substrates and a comparison is made between MLs with and without a 20 nm seedlayer.
Some basic properties of the Co/Pt and Co/Pd multilayers are given in table 1.

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  A process based on argon sputtering has been developed for the production of Pt/Co multilayers with high coercivities. Loop squareness and polar Kerr rotation are not degraded by the processing and multilayers with square loops, polar Kerr rotations of ›0.3° and coercivities approaching 6 kOe have been prepared.

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  Methods of Curie temperature control in Pt/Co multilayers have been investigated and the results used to prepare stacked Pt/Co double multilayers in which each component multilayer has an independently-controlled coercivity and Curie temperature. Such stacked multilayer systems represent a first step towards a laser-modulated direct overwrite structure.

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  The authors have studied the structure, magnetic and magneto-optical (MO) properties of MnBi doped with rare earth elements (Ce, Pr, Sm, Nd, Tb, Dy and Ho) thin films. It is found that the, MnBiRE (RE= Ce, Pr, Sm) films have larger Kerr rotation angle θ_k than the MnBiRE (RE=Nd, Tb, Dy and Ho) films. The value of θ_k decreases with the increase of doped amount of RE elements. When RE (RE=Ce, Pr and Sm) were doped with into MnBi films in the range of RE concentration x=0.02-0.25, the Kerr rotation angle θ_k can reach over 2° at λ=633nm and room temperature. The reason of the large enhancement of the Kerr rotation angle is discussed based on the electron transition between 3d -6p bands of MnBi alloy.

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  Magnetic perpendicular anisotropy of RF-sputtered amorphous TbFe/SiN thin films have been investigated. Anisotropy constants were evaluated from both magnetization curves and magneto-optic effects dependences on in-plane magnetic field. Significant difference was observed between the magnetic anisotropy of the whole film and that measured from its surface, and the difference depended on preparation conditions and film thickness. It was proposed that the incoherent magnetization rotation in external field was induced by very thin highly-magnetized surface layer, which was exchange coupled with the film. Therefore the observed value of the anisotropy energy differs from the intrinsic anisotropy value of unoxidized volume.

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  We summarize the effect of alloying elements in Al alloy reflection films for quadri-layered MO disks. The addition of group 4A∼7A transition metal elements to Al films is the most effective to improve corrosion resistance and to reduce thermal conductivity. It is confirmed by practical tests that reliability and recording sensitivity of MO disks is extremely improved by using Al-group 4A∼7A transition metal alloy reflection films.

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  In this paper, the temperature dependence of magnetic and magneto-optic (MO) properties of light rare earth (LRE)-heavy rare earth (HRE)-FeCo / HRE-FeCo has been investigated. The shapes of Kerr hysteresis loops were lead to great changes as temperature varied. The Kerr angles of couple-bilayered films were shown different decreasing tendency as compared to those of single-layered films when temperature was increased. It was found that the exchange-coupled action has a profundly contribution to Kerr angles through the temperature range (-30° ∼110°C).

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  Epitaxial Fe/Pt layered films were produced by DC magnetron sputtering onto polished [001] MgO single crystal substrates. A 100 Å Fe, 100 Å Pt single bilayer film and a multilayer with 30 bilayers of 46 Å Fe and 59 Å Pt were examined using transmission electron microscopy. Plan-view electron diffraction and x-ray diffraction results from the bilayer indicate an orientation relationship such that Pt (001) || Fe (001), and Pt [100] || Fe [110]. Cross-section electron diffraction from the multilayer shows a superlattice structure along [001] (out-of-plane) and indicates partial in-plane strain relaxation of the layers away from the average in-plane lattice spacing, implying a slight tetragonal distortion of the layers. High resolution cross section imaging indicates an epitaxial structure consisting of BCC Fe and FCC Pt, with the same orientation relationship as seen in the bilayer. These results show that high quality epitaxial Fe/Pt multilayer films can be produced in this way.

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  A model assuming exchange coupled layers is used to evaluate the interlayer exchange coupling strength, A₁₂(t_Pt), and the effective uniaxial anisotropy field, H_eff(t_Pt), within each Co layers as a function of the Pt thickness, t_Pt, from the perpendicular ferromagnetic resonance spectra for a series of Co/Pt multilayer films. It was found that A₁₂(t_Pt) decreases exponentially with t_Pt having a characteristic length, t₀ ∼ 7 Å, indicating the importance of the polarization of Pt to mediate the interlayer exchange coupling between the Co layers. The decrease of H_eff(t_Pt) with the increase of t_Pt also follows an exponential function of t_Pt with a decay length, τ ∼ 13 Å, suggesting that the surface interaction on each Co/Pt interface is not fully developed unless the Pt layer thickness is greater than τ.

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  Magnetic properties of Kr-sputtered Tb/FeCo multilayers were studied. Perpendicular magnetic anisotropy K_U and coercive force H_C are improved by Kr-sputtering. The perpendicular magnetic anisotropy improvement is discussed from the point of view of a multilayer structure, an inverse magnetostriction effect and single-ion anisotropy. The multilayer structure and the internal stress are not changed by the Kr-sputtering. K_U improvement with Kr-sputtering is not observed in Gd/FeCo multilayers. Therefore, K_U improvement with Kr-sputtering is caused by the single-ion anisotropy improvement. No difference in Kerr rotation angle, between Kr-sputtered and Ar-sputtered films, is observed, ranging from 400nm to 1000nm wavelength.

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  A systematic study on structure, magnetic and magneto-optical properties of Fe/Pt and FeCo/Pt multilayer films has been performed. It is found that the microstructure observed by cross-sectional TEM as well as the effective perpendicular anisotropy K_eff varied according as substrate-deposition-temperature. In Fe/Pt multilayer film deposited on the substrate above room temperature, a fine columnar structure were discerned and the perpendicular anisotropy was fairly large. In the sample grown on a cooling substrate, however, the structure with irregular small crystal grains appeared instead of a columnar structure and the K_eff reduced. This result implies that the columnar microstructure contributes to the perpendicular anisotropy of multilayer films.

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  Observations of micromagnetic dynamics in magneto-optical recording media have been performed using a static tester and a loop tracer. The magnetization reversal, domain structure and annealing treatment of amorphous rare earth-transition metal (RE-TM) alloy films as well as multilayered cobalt-platinum (Co/Pt) thin films have been studied. The magnetization reversal was investigated in both nucleation-dominated and wall-motion-dominated media. The degree of jaggedness of various domain structures has been compared in terms of the fractal dimension of domains. We find that the magnetization reversal processes are intimately related to the jaggedness of domain surface. The fractal dimension increases monotonically from wall-motion-dominated films to nucleation-dominated films. The relationships between the hysteresis loop and the reversal process are also discussed.

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  We have used in situ polar Kerr effect measurements to study the perpendicular magnetic behavior of MBE-grown transition metal (TM = Au, Ag, Cu, Ir and Pd) overlayers deposited on single-crystal Co films. The Co films were grown on Pd buffer layers in both the (111) and (001) orientations. Cobalt thicknesses ranged from 2 Å ≤ t_Co ≤ 10 Å for the (111) orientation and were 2 Å and 4 Å for the (001) orientation. The uncovered Co displayed a perpendicular easy-axis for all thicknesses in the range 2 Å ≤ t_Co ≤ 6 Å in the (111) orientation, but only for t_Co = 2 Å in the (001) orientation. After growth of the Co, subsequent deposition of just ∼2 Å of any TM overlayer increased the perpendicular coercive field and ellipticity dramatically for Co(111), while for the Co(001) the sample became nonmagnetic or the magnetic moment was driven in-plane. We attribute the sharp peak in the coercive field of the Co(111) films we observe at ∼1 monolayer (ML) coverage for all TM studied to date to a change in the electronic structure of the TM overlayer at ML thicknesses.

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  We report the development of Co-Pt alloy films with large perpendicular anisotropy and high coercivity (›4 kOe) grown directly onto amorphous, non-metallic substrates. This has made possible magneto-optical recording in these alloys with CNR values exceeding, for the first time, 57 dB at 488 nm.

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  The solid-state phase formation process by thermal annealing of the multilayered films consisting of two kinds of unit lamellae, Pt/Mn/Sb and Mn/Sb, was investigated by means of x-ray diffraction and transmission electron microscopy. The magnetization loops of the films were measured at room temperature by using a vibrating sample magnetometer. The films consisting of the two phases of PtMnSb and MnSb or Mn₂Sb were successively produced. The relative amount of the PtMnSb and MnSb or Mn₂Sb phases was considerably affected by the initial stacking pattern as well as the substrate temperature. In addition, these conditions brought a substantial change in the preferred orientation of the MnSb and Mn₂Sb phases through the nucleation process. The magnetic anisotropy of the films changed significantly in accordance with the film structure such as the preferred orientation and relative phase amounts.

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  The reliability of a Pt/Co Magneto-Optical disk with a simplified structure (poly-carbonate/ZnO/PtCo/UV resin) was examined with accelerated tests. After aging for 2000 hours at 80°C with 85% RH, Carrier to noise ratio was scarcely lowered, while the value of block error rate increased because of extra noise which was produced by local defects. The defects did not seem to be pin-holes as seen in the case of rare earth-transition metal alloy films. According to the Arrhenius plots of accelerated tests, the life time of the disk is estimated to be more than 10 years at room temperature.

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  The novel evaluation method of recording characteristics has been realized for the light intensity modulation (LIM) DOW using 4-layer MO media. The recording characteristics has been grasped as the read-back signal level on the two dimensional overwrite power plane. Analyzing the distribution of these levels, the power margin of overwriting has been made clear and the permissible power region to be overwritten and the evaluation method of the optimal recording power are defined and estimated.

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  Direct overwrite is one of the principal ways to improve the data transfer rate of magneto-optical disks. One direct overwriting method is light intensity modulation using exchange-coupled five-layer film. The intermediate layer in this method is important for controlling the interface-domain wall energy between the memory and writing layers. We fabricated an overwritable five-layer film which uses Cu-doped DyFeCo for the intermediate layer. By changing the Cu content in this film, it is possible to control the interface-domain wall energy. For a Cu content of 45%, we obtained a wide power margin for a carrier-to-noise ratio which exceeds 45dB.

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  Exchange coupling force between magnetic layers plays a crucial role in overwritable media using light intensity modulation. To control the force, an additional intermediate layer having low magnetic anisotropy has been fabricated conventionally. The plasma treatment with nitrogen was tried for controlling the exchange coupling. This method has the possibility of cost reduction and improvement of sensitivity in comparison with conventional method. The exchange coupling was well controlled by the parameters of discharge. The disks obtained in this study showed sufficiently good read-write characteristics.

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  A magneto-optical disk with the functions of direct overwriting by light intensity modulation method and of magnetically induced super resolution readout was realized by utilizing an exchange-coupled multilayer film. Magnetic hysteresis loop measurement clarified that these two functions can work independently at different temperature ranges. Write and read characteristics measurement also proved this and an equivalent CN ratio with that of a disk without direct overwrite function was obtained.

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  Laser power modulation direct overwrite (OW) on a Co/Pt multilayer was successful by the magneto-statically coupled OW method. In order to use the Co/Pt multilayer as the storage layer in this method, the magnetization reversal temperature was adjusted by changing the thickness of the Co layer and a small switching field was accomplished by making the total thickness thinner. An OW CNR up to 32 dB with the conventional rare earth-transition metal biasing layer was obtained for the Co/Pt multilayers stacked 2 or 4 times.

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  To achieve a higher density recording on the overwritable exchange-coupled quadrilayer MO disk, the overwrite recording characteristics using 680nm laser diode were investigated. High recording sensitivity is obtained on the disk with about 1000Å magnetic film. CNR more than 46dB is obtained at 0.66μm mark length, and 0.5μm/bit recording with bit error rate less than 1×10^-5 succeeds at 1.2μm track pitch zone.

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  In the light intensity modulated overwriting method with exchange coupled multilayers, the erasing area surrounds the writing area because the erasing temperature is lower than the writing temperature. Therefore, the data on the adjacent track might accidentally be erased when informations are recorded on a track at a high track density. This Thermal Cross-Talk(TCT) can be effectively reduced by controlling write pulse shape and by applying a UV-resin coating on the top of the disk. By such measures, a high track density up to 1.35μm track pitch was proved feasible.

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  We have achieved a carrier-to-noise ratio of 67 dB (30 kHz bandwidth) on magneto-optic disks that utilize two thin magneto-optic layers. The improvement came primarily from the writing noise reduction. This noise reduction is explained through the statistical averaging of the written magnetic transition positions in the two recording layers. The disk writing noise can be further reduced when more active layers are used in the disk structure. This noise reduction scheme can be utilized in other kinds of recording disks.

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  Thermomagnetic recording process is simulated by a dynamic algorithm based on the consideration of time-dependent temperature distribution and balance between magnetic forces. Two compositions Tb₂₈Fe₆₀Co₁₂ and Tb₂₂Fe₆₈Co₁₀ are studied. The time evolution and the field-strength dependence of the recorded pattern are presented and a discussion of the simulated results is made from the perspective of temperature dependences of magnetization and coercive forces for both compositions. The recording mechanism is revealed by analyses of elementary magnetic forces in the two compositions.

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  The recording properties of evaporated Dy-FeCo based MO disks were investigated for a broad riation of compositions. The carrier-to-noise-ratio, the write and erase thresholds and the domain jitter we determined in dependence on T_c and T_comp using a laser light and a magnetic field modulation recorder 820nm wavelength. Dy-FeCo exhibited a very good recording characteristic such as good sensitivity, high CNR ≥ 55dB, good field sensitivity and a low jitter.

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