The bilayers composed of Tb-Fe-Co and Co-Cr alloy layers have been prepared by using a facing targets sputtering apparatus. The specimen films revealed apparent magnetic coupling between ferrimagnetic Tb-Fe-Co and ferromagnetic Co-Cr layers. The bilayers revealed Kerr rotation angle as large as 0.6 deg. at the wavelength of 633 nm.

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  The phenomenon of rotational magnetic anisotropy in the plane of amorphous Gd-Co films was observed. The saturation magnetization, perpendicular and rotational anisotropy constants, torque curves were investigated for different composition films. The experimental and theoretical results suggest that a fine stripe domain structure existed in transcritical films is responsible for rotational magnetic anisotropy.

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  We have sputter deposited amorphous CO_1-x-Er_x films with 5≥22 and studied their magnetic and magneto-optic properies. The magnetization first decreases with increasing x reaching a compensation for x= 17 at 5 K. The Er moment was found to be 7.0 μB indicating non-collinear spin structure. The field dependence of magnetization shows that for x= 15.8 and 17.9, at a critical field H_cr1 the antiferromagnetic coupling is broken. The results are discussed in terms of the known model. The polar Kerr rotation at 633 nm wavelength shows a monotonous decrease with increasing x implying that the rotation arises mainly from the Co atoms.

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  We prepared Co-Au granular alloy films with compositions ranging from 5 to 38at.% Co on glass substrates by a sputtering method and measured their magneto-resistance and magneto-optical Kerr rotation (Φ_K) spectra at RT. As a result, it is found that 20at.% and 28at.%Co-Au films show a large peak at about 3.4eV and small peaks due to the plasma enhancement by the Au matrix at about 2.5eV, respectively. By annealing, the shape of the Φ_K spectra became to similar to each other in all the films; namely, two Φ_K peaks appear at about 2.0eV and 3.4eV. Thus, Φ_K spectra is quite different from those of Co ultra-thin films and bulk Co.

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  The magneto-optical properties of Fe, Co films deposited on fused quartz substrates have been investigated. The AFM observations and ellipsometric data show that the film makes island structure on the substrates in the early stages of deposition. A new peak appears in the spectra of the real parts of ωσ_xy for films thinner than 60 Å. It shifts to the higher energy side with decreasing thickness.

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  Magneto-optical thin films with composition Tb-Fe-Co-Cr are coated on AI foil, Co-base and Fe-base amorphous ribbons. The thickness of M-O thin film is in the range from 200nm to 1000nm, which is sandwiched between two AlN layers with thickness 100nm to prevent it from oxidation. The Kerr hysteresis loops of M-O films were measured with wavelength from 500nm to 860nm, and the peak applied field was. 9kOe. The Kerr rotation angles of M-O films deposited on Co-base and Fe-base amorphous ribbons are improved by a factor of 2.6 and 2.86 respectively at wavelength 780nm. The Kerr angles of M-O films are enhanced markedly by either Co-base or Fe-base amorphous ribbons.

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  Magnetooptical spectra have been studied for photon energies between 1.2 and 6.4 eV in bulk crystals of undoped and Pt-doped MnSb. Kerr rotation ofundoped crystals showed a prominent zero-crossing behavior around 4.5 eV. The zerocrossing energy moved to 4.1 eV in Pt-doped samples, which were explained by the averaged spectra of separated two phases of MnSb and PtMnSb.

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  By using the magneto-optical and transmission-ellipsometric methods, giant anisotropy in both optical and magneto-optical properties was found for the singl crystal Cd_1-xMn_xTe (x=0.45). Two orthogonal axes, E_⊥ and E_|| were in the (113) plane, and along the [-47-1] and [21-1] directions, respectively. Both transmission-ellipsometric and magneto-optic Faraday rotation spectra located peaks at the same about 2-eV E_Mn position, that was in the gap between the conduction and valence bands. In discussion, E_Mn was attributed to the optical transition of Te p → Mn d_↓, and several possible mechanisms for the anisotropy phenomena were suggested and studied. A general and analytical equation was given to calculate the anomalous anisotropy of the Faraday effect, showing good agreement with experimental results. The equation can be used to explain other magneto-optical anisotropic properties of the system.

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  Photoinduced irreversible change in an optical absorption α is observed for a bulk single crystal and a thin film of yttrium-iron garnets (YlG) over the spectral range 600 or 700-2000 nm and over the temperature range 80-200 K. In some specimens, coexistence of phtoinduced and dark Δα-effectis found at low temperatures. Experimental data are discussed within a simple phenomenological model.

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  A recent study of the magneto-optic properties in fcc cobalt indicates that the polar Kerr activity in a photon energy range from 2 to 5 eV is much higher than that of the hcp phase. The samples used for this measurement were about 1,000 Å thick e-beam evaporated films grown on a Cu seeding layer. Structural analysis using grazing angle X-ray diffraction, TEM, XPS, AES, and RBS indicates that the films are single Crystal of high quality and there is no indication of interdiffusion between the layers. The present result provides the confidence in the data published for the magnetic and magneto-optic properties of the fcc Co phase.

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  A magneto-optical disk memory with a magnetic super resolution (MSR) method can get large capacity beyond the optical limitation. One of the MSR methods is realized by a readout layer that shows in-plane magnetization at room temperature and perpendicular magnetization above a specific temperature. Here, the recording and readout characteristics of the MSR disk are investigated and a magnetic field modulation recording method is examined. The recording density reaches 2.5Gbit/inch² with a 680nm wavelength laser.

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  The methods for capacity enhancement using commercially available laser are concisely reviewed. The issues on time-to-market and cost for producing drives based on these methods are discussed. The tricks on designing media for 8X capacity imposed by the above factors are open for creation

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  We have demonstrated that the expected capacity increase from PPM to PWM recording channel can be fully realized in the next generation optical recording drives provided that the critical media characteristics are tightly controlled, and advanced read/write techniques are properly implemented in the channel. For future products with 10x and higher capacities, the media characteristics such as thermal sensitivities and groove noise must be greatly improved to retain the advantage of advanced recording techniques used in PWM or PAM channels. We have demonstrated that 10x capacity increase can be achieved with a PWM channel and short wavelength lasers if these improvements are made [1].

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  In order to achieve higher areal density recording, both land and groove area recording ( Land/Groove recording ) technology has been developed. In the Land/Groove recording method, the combination with crosstalk canceller and PRML technique has a potential for over achieving 10X MO recording in realizing larger capacity. Moreover, it is also possible to accomplish 16X MO recording, using the blue green laser head combined system.

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  We have analyzed the jitter characteristics and disk tilt tolerance of an MO system capable of 7 times higher areal density MO recording for various paris of bit length and track pitch using a green light source. The minimum jitter of 8% with no disk tilt was obtained at a bit length of 0.3 μm and a track pitch of 0.75 μm. The disk tilt dependence of the jitter was measured for each of the above conditions. The disk tilt margins under any conditions were small compared to that of conventional MO disk systems. The tilt margin of more than ±0.5 deg can be ensured with the aid of a two dimensional skew servo system. Based on these results the advantage of a blue light source is discussed. Using our disk optimized for green light, the SNR estimated for blue light is 2 dB smaller than that measured for green light. The influence of the SNR degradation upon jitter is not very large. We expect that the combination of a blue light source and a low NA objective lens will enlarge not only the disk tilt tolerance but also other tolerances limited by aberrations.

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  We consider the macroscopic and microscopic theory of the Magneto-Optical Kerr Effect. It is shown that the Kerr effect is zero without both spin-splitting and spin-orbit coupling. The origin of peaks in the Kerr signal is discussed. For the transition metals Fe, Co and Ni these peaks arise from interband transitions. Results for the fcc and hcp forms of Cobalt are presented and compared. Fair agreement with recent experiments is found. The effect of the lattice parameter and the Drude term on fcc Co is also shown.

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  The magneto-optical (MO) properties of thin epitaxial Fe films (0-20 Å) on Au and GaAs have been investigated. The Au sandwiched (001) Fe films show an oscillation of the magneto-optical properties as a function of the film thickness. This oscillation can not be observed for Au sandwiched (110) Fe films. In addition to the oscillating term an off-set exists in the plots of the complex Kerr rotation versus film thickness. The shape of the measured thicker film spectra is in agreement with those calculated from a first order linear approximation using the bulk dielectric properties as found in literature. The films directly deposited on (100) and (110) GaAs showed a linear relation between film thickness and MO properties. A magnetic dead layer of 5 Å appears to exist.

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  Dielectric AlN thin films have been prepared by reactive sputtering method, using a facing targets sputtering apparatus with a DC power supply. The AlN films deposited at the ratio in pressure of nitrogen of 21 % exhibited refractive index as high as 2.35 and revealed sharp rocking curve of x-ray diffraction pattern with full width of half maximum as small as 5 deg.

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  The reliability and the sensitivity of quadri-layered MO disks with an AITa reflection layer and those with a pure Al reflection layer were evaluated by the PCT environmental test. In the case of glass substrates CNR of media with a pure Al reflection layer decreased faster than that with an AlTa reflection layer. Optimum writing power increased steadily, and finally it exceeded the system's maximum laser power for both kinds of media. However, initial writing power of media with an AlTa reflection layer is much lower. Therefore, an AlTa reflection layer can maintain higher CNR and offers a large margin. The recording layer in the media with an Al layer degraded more than that with an AITa reflection layer. This can be attributed to the higher corrosion resistance of an AlTa reflection layer.
  CNR of media fabricated on PC substrates decreased faster than those on glass substrates in the early stage of the PCT test. No significant difference between the two kinds of media was observed in this case.

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  In this paper, a new type of MSR using the combination of exchange coupling and magneto-static coupling was proposed. This method did not use a mask in the readout spot, but reversal of magnetization at high temperature area. The reversal changed the signal interference between recorded marks and their neighboring magnetic domains, and led to good super resolution performance without any readout field. Its waveforms were expressed as the composition of differential signal and non-differential signal, and their ratio depended on reading power. Cross talk was lower than FAD, and became lower by using thicker readout layer.

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  Composition and thickness dependence of GdFeCo/TbFeCo double layer films for magnetically induced super resolution were studied. The resolution depends on the composition and thickness of the GdFeCo readout layer in particular. Varying Fe-Co ratio and the thickness of GdFeCo, sensitivity to recording magnetic field was investigated. Cross-talk of 100 nm readout layer was 12 dB less than a conventional disk.

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  The relationship between copying characteristics of recorded domains and readout characteristics was investigated for a single masked rear aperture detection (S-RAD) disk with a quadri-layer magnetic film. Higher linear density comparable to a double masked rear aperture detection (D-RAD) disk was obtained with S-RAD consequently.

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  We propose an exchange-coupled magnetic trilayer film, which is composed of a readout layer, an intermediate layer, and a writing layer, to achieve magnetically induced super resolution (MSR) by rear aperture detection (RAD). The film doesn't require several kilo oersteds of magnetic field to align the magnetization direction of a readout layer. We obtained a carrier-to-noise ratio (CNR) of over 40 dB for a 0.4 μm mark length (0.8 μm mark pitch) and cross-talk of under -40 dB for a 0.78 μm mark length on 0.8 μm effective track pitch.

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  A linear scalar model is presented in this study to calculate carrier to noise ratio (CNR) of magnetically induced super resolution (MSR) for various sizes and shifts of apertures using rear aperture detection (RAD) and front aperture detection (FAD). Margins of the mask and aperture sizes are -16 to 25% and -15 to 17% of the size of recorded pits for FAD and RAD, respectively.

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  Two enhancements have been developed for the heat conduction solution using Fourier-transformed Green's functions. These enhancements allow for more accurate modeling of the laser beam found in practical MO systems. The first is the addition of a “pulse train” typically used for write compensation. The Fourier transform of this pulse type is modified to reduce the Gibbs phenomenon and to eliminate transition points at the discontinuities. The second is the addition of an apertured and wavefront aberrated laser beam. Also, a study of the formation of FAD masks in MSR disks is presented.

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  Durability of mark-edge recording magneto-optical disk is studied. Rare-earth rich TbFeCo film shows a very good write/erase cyclability more than 10⁶ repetition in a jitter bucket curve test. By applying a novel protective overcoat resin and a high grade poly-carbonate substrate, there shows no degradation after 1000 hours 80°C, 90%RH accelerating test.

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  Magneto-optical disks with metal guiding layers have spiral guiding bands which works as slits placed close to recording layers. The divided push-pull signal has been improved by using Cr as guiding layers. The disk noise for the track pitch of 0.85 μm is lower than that of a pre-grooved glass disk with the track pitch of 1.6 μm. It is confirmed that the disk noise which arises at the edges of the spiral Cr guides is very small. The maximum CNR of 47.3 dB and 54.0 dB were obtained at 3.73 MHz and 1.0MHz for the track pitch of 0.85 μm. The magnetic domains are restricted in the recording regions because the cross-talk at 1.0 MHz has been suppressed to less than -23.4 dB even though the readout laser spot size is about 1.4 times as large as the track pitch.

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  In order to increase the recording capacity the mark edge recording and (1, 7)RLL code are employed in the second generation ISO/IEC optical disk standard. However this recording method degrades groove parameter at ROM area because (1, 7)RLL code has long Tmax which causes recording pattern of combination of long pits and short spaces. New (2, 5)RLL code whose Tmax is small were developed. Because Tmax/Tmin gets close to unity, the information capacity of the code is small so that detection window width becomes narrow. Because narrow band signal to noise ratio is large and jitter is small in ROM area, the window margin of (2, 5)RLL code written in ROM area is same as that of (1, 7)RLL code written in MO area when both codes are recorded in the same recording density. The window width of (2, 5)RLL code is 0.4Tb and Tmin is 1.2Tb where Tb is one bit length of information bit.

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  A write compensation scheme for narrow-track optical recording is proposed theoretically. This approach uses the edge-position shift to suppress crosstalk; it achieves 35% higher recording density without any additional head components.

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  Relationships between noise level and writing layer thickness for the exchange-coupled double-layer magneto-optical(MO) disk were investigated. Using the inverse magnetization direction copying mode is effective in reducing the writing layer thickness without increasing the noise level. Due to reducing the magnetic layer thickness to 60 nm in the novel MO disk, θ_k enhancement by heat-sink layer is achieved. Read/write characteristks for a novel MO disk with exchange-coupled double-layer were compared with those for a conventional quadrilayer MO disk at 690 nm wavelength. C/N ratio for this MO disk shows a 1.5 dB improvement over that for a conventional one in all the frequency range. Leading edge jitter for this MO disk is lower than that for the quadrilayer MO disk, because of its higher C/N ratio and suppressed thermal interference.

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  Direct overwrite (DOW) performance with a short wavelength laser was estimated numerically for the magneto-statically coupled method. When the laser spot size was reduced, large leakage field was generated in the medium. The leakage field modulation was estimated to be increased from 80 Oe to 180 Oe with decreasing the wavelength from 830nm to 415nm. From this result, the improvement in the DOW CNR over 45dB was expected. It was also found that the improvement in the leakage field was less than that expected ideally, because of the reduction of the thermal diffusion to the auxiliary layers.

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  We have attempted to obtain the parameters of the recording laser waveform by computer simulation. For the laser waveform, we have used seven kinds of control factors. For the fluctuation of the mark shapes, we have used three kinds of noise factors. To find the optimum control factor values, we have calculated various mark shapes using a computer simulation model which we have already provided for the DOW-MO disk. We have calculated the mark shapes of each combination of control factors under the nine combinations of noise factors. Judging from the controllability of the mark edges, we have obtained the best, that means 'the most robust', control factor values. The best control factor values are eventually the same as the standard values which we have already published in Reference [1].

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  When mark edge: recording with the technique of thermal interference uniforming (TIU) is applied to direct overwrite (DOW) magneto-optical (MO) disks, the disks should be matched with this recording technique. In other words, the laser power recording condition should satisfy both the TIU condition and the DOW condition simultaneously. In order to examine the disk and drive matching, we have measured the temperature dependence of the recording properties of DOW-MO disk, for instance the recording laser power. When mismatched, either the disk or the drive should be retuned. The disk thermal properties may be changed for retuning. In the drive the laser power of the writing waveform may be changed for retuning. As a result of efficient matching, we report that a DOW-MO disk is matched well with the drive using TIU.

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  Magnetization reversal analysis on quadrilayer films by Faraday loop measurement revealed a peculiar magnetic reversal behavior that occurs in the initializing process which is explained in terms of magnetic energy. And it was also clarified that the initializing process depends strongly on the switching layer and is controllable and an example of adjustment of the initializing temperature and the low write temperature was shown.

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  The performance of future generations of MO (Magneto-Optical) recording media will depend more strongly on domain edge features because of pulse width modulation (PWM) encoding requirements and higher domain densities. Diect observation of these features would help greatly in correlating media performance to domain characteristics. This paper describes domain observation using Lorentz transmission electron microscopy (TEM) with a new sample preparation method; domains were dynamically written in thin films deposited on a large salt crystal substrate. Domains written both in a SiN/TbFeCo/SiN thin film stack and in a SiN/TbFeCo/SiN/Al-Cr thin film stack were examined and compared. Some relationships between domains and writing conditions were found. A resolution of near 10 nm was reached. It was also found that domain walls and microstructures, which are most likely columnar structures, were observed at the same time using high resolution Lorentz TEM.

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  This paper describes the design of a novel, combined R-θ scanning laser microscope and optical disk tester, which is to be used for the testing and evaluation of optical recording media. The instrument is capable of perfoming a range of standard read/write tests, whilst simultaneously yielding a microscopic image of the recorded bit structure with sub-micron resolution. A range of optical media can be investigated including magneto-optic, phase-change and write-once formats such as dye-polymer media.

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  We have developed a new technique of using a torque magnetometer to obtain M-H hysteresis loop of a uniaxial magnetic material. The hysteresis curve was obtained from the loop of the torque τ measured as a function of an applied field H, when the direction of the applied field φ, was 9° from the uniaxial orientation. This technique was applied to obtain the hysteresis curves of several Co/Pd multilayer thin films. For a sample having a high anisotropy field, the present method was able to obtain its magnetization curve with a greater accuracy than a conventional VSM. This method, for example, has shown a high sensitivity of about 1 × 10⁻⁶ emu in measuring the magnetization curve of (2-Å Co/9-Å Pd)₂₇.

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  A method for analyzing the dynamics of domain formation in magneto-optical recording media was established using measurement of the extraordinary Hall effect. A magnetic domain was written on a cross-shaped magneto-optical film having an area of 3.4×3.4 μm² at the center of the cross, and the extraordinary Hall voltage was monitored during thermomagnetic writing. Two kinds of TbFeCo films were investigated. For RE-rich film, the nucleated domain expands with the expanding Curie disk in the heating process, and then shrinks in the cooling process. For TM-rich film, on the other hand, the domain cannot follow the Curie disk and, therefore, does not appear during the heating process. The domain in this case is formed in the cooling process and does not show any tendency to shrink.

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  Epitaxial, (001) oriented Fe/Pd multilayers were deposited by DC magnetron sputtering onto single crystal (001) MgO. Annealing resulted in the formation of c-axis oriented ordered intermetallic compounds with the tetragonal L1_o crystal structure and the orientation relationship (001)FePd || (001)MgO and [110]FePd || [110]MgO. Accompanying the formation of this phase was a switch from an in-plane to an out-of-plane magnetic easy axis with a perpendicular magnetic anisotropy of 6x10⁶ erg/cm³. The magneto-optic Kerr rotation of ordered FePd is maximum near 1.6 eV and minimum near 2.9 eV, with values of 0.29 and 0.05°, respectively.

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  A near-field optical technique, using a new type of Solid Immersion Lens (SIL), has been developed and applied to the writing and reading of domains in a magneto-optic material. The SIL is a truncated glass sphere which serves to increase the numerical aperture of the optical system by n², where n is the index of refraction of the lens material. By mounting a 1 mm SIL on a slider, we have been able to fly the SIL on a magneto-optical disk. We have demonstrated writing and reading with such a lens at data rates exceeding 1 Mbit/s with a carrier-to-noise ratio of approximately 50 dB. Using a 830 nm laser and a n = 1.5 SIL, the focused spot size was reduced by close to a factor of 2 and was measured to be 600 nm.

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  This paper reports properties of a homogeneously aligned liquid crystal microlens of which the focal length is controlled by applied voltage and the response properties both without and with a bias voltage, which are very important for applying the microlens to the optical head. It also describes the design of fresnel lens with liquid crystal microlens to expand its diameter and further describes the possibility of applying the liquid crystal microlens to the optical heads.

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  Magnetically induced super resolution (MSR) with double masks has been realized without the external magnetic field during readout. This new type of MSR is achieved in disks having three exchange-coupled magnetic layers including inplane magnetization films. With these disks, a high C/N of 45dB for a mark length of 0.40μm is obtained, making it possible to reduce crosstalk.

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  A magneto-static coupled triple-layered medium was fabricated on a photopolymer-glass substrate by RF magnetron sputtering. The medium is composed of a reading layer, a non-magnetic intermediate layer, and a writing layer. The reading layer shows in-plane magnetization at room temperature and perpendicular magnetization at high temperature. Magnetically-Induced Super Resolution (MSR) was achieved by formation of a perpendicular magnetization mask in addition to an in-plane magnetization mask without applying a readout magnetic field. A carrier-to-noise ratio (CNR) of 44 dB was obtained for a mark length of 0.38 μm.

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  In the magnetically induced super resolution, a rapid change in the readout signal was observed. The rapid change is explained by a domain collapse model. We proposed a new readout technique which utilizes the rapid change in the signal. The technique can reduce the readout jitters and enables high signal to noise ratio detection. Combination of mark position recording and a write-read channel with small detection window enables the high density recording of 0.5 μm/bit or less even if the carrier to noise ratio of the disk is not sufficiently high.

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  To broaden magneto-optical disk application, the most important issue is a remarkable increase of recording density. This paper firstly opens magnetic multi-valued (MMV) MO disk. Especially, here, quadri-valued MO recording was studied by a field modulation overwriting method using a new layer structured disk. Such attempt gives very attractive approach to make double or more higher capacity disk not depending on laser wavelength.

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