Continued scaling of existing information storage paradigms appears to be near its end. A slowdown in the increase in areal storage density in magnetic hard disk drives, a system at the forefront of storage density, has been apparent in the last eighteen months and is likely to be seen in optical and solid state systems as well. However, this slowdown is a consequence of the engineering paradigm itself rather than any manifestation of fundamental physical limits on storage system performance. This paper suggests that storage densities orders of magnitude greater than those demonstrated today are possible.

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The 3D-MO (3-dimensional Magneto-Optical Recording) national project ended with a great success of achieving 100 Gb/in² areal recording density with a new scheme of Double-MAMMOS (double recording layer MAMMOS, MAMMOS: magnetic amplifying magneto-optical recording system). A high performance write and read (W/R) tester equipped with a newly developed optical flying head (OFH), a low noise wide band photo detector IC (PDIC), and a high speed beam access system was developed. First surface (FS) MAMMOS disks for short wave length (405 nm) and high NA (0.9) optical system were also successfully developed and succeeded in a W/R test at 52 Gb/in² areal density.

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The effect of the side-wall-annealing process on the domain wall mobility of a track-wobbled DWDD disc was investigated. Using a red laser and NA of 0.60, we obtained sufficiently low bit error rate and wide recording power tolerance on a one-side-wobbled land/groove substrate. Furthermore, wide tolerance of groove duty for characteristics of both MO and address was obtained. Track-wobble has no influence on the domain wall mobility and the side-wall-annealing technique is useful even for a track-wobbled high density DWDD disc.

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Double-MAMMOS is an excellent method to increase memory density for MO recording. This method modifies the usual MAMMOS technique by applying double recording layers. Written domains in each recording layer can be selectively copied and expanded in a reading layer. By this method, memory density can be doubled. However, it is necessary to record twice, recording separately into two layers. Therefore, we propose a new type Double-MAMMOS disk, applying a quadri-value recording system to write the double recording layers with a single writing process. By applying a newly designed Double-MAMMOS disk, we can obtain a high density and high performance MO disk. To satisfy both functions of Double-MAMMOS and single writing process, we adapt the dependence of magnetization on temperature of films.

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Wall structure and energy have been simulated for the Domain Wall Displacement Detection (DWDD), and the front process and the rear process under temperature gradient have been considered. For the front process, when the mark length is comparable with the domain wall width in the displacement (D) layer, the domain copied on the D-layer from the memory layer collapses. By making the D-layer thin, the minimum mark length for which the domain wall displacement occurs can be shortened. For the rear process, we confirmed that by inserting the control layer between the D-layer and the switching layer, the mark length with which the ghost signal is suppressed becomes longer. By making the anisotropy energy constant in the D-layer increase, improvement in the DWDD process is expected.

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To eliminate the time required for test data recording before test read, we studied test read approaches using as-deposited MAMMOS media, i.e., without recording the pre-determined test data onto the media. We consider the accumulation of the absolute values of this difference in the two moving averages as a good criterion to obtain desirable readout laser power. The results from our experiments suggest the proposed method is effective as long as the as-deposited conditions can be well-controlled.

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Thermally assisted or hybrid magnetic recording system is expected to be a data storage device with high areal density beyond 1 Tb/in². Several features of the hybrid recording are treated, such as high resolution recording capability by sharp thermal gradient, and pico-second order high-speed magnetization reversal. Since the hybrid recording solves the head field limit problem, the high magnetic anisotropy (K_u) materials with order of 10⁷ erg/cm³ are used for the hybrid recording media. We discuss the candidates of the high K_u materials, FePt and CoPt L1₀ ordered alloy, Tb-Fe-Co amorphous, and Co/Pd multilayer thin films.

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We review the fundamental issue standing in the path of continued improvement in areal density in magnetic hard disk drives, namely, the superparagmagnetic effect. We also describe some of the optical components of a hybrid or heat assisted magnetic recording system, which is one possible solution to this technical challenge. We note the potential for heat assisted magnetic recording to achieve increased information storage densities at reasonable signal to noise ratios. Finally we identify an issue exacerbated by the introduction of thermal assistance of magnetic recording, namely that of the additional thermal load on the slider. We describe an experimental apparatus that we have employed to quantify the temperature rise in a slider when it is subjected to particular thermal loads at various locations on the slider body.

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Thermomagnetic recording process was simulated for Tb_c(Fe₇₂Co₂₂)_100-c media by using Huth's model modified to be applied to the magnetic field modulation (MFM) recording method. In the case of the recording with 0.4μm-diameter laser spot and a single pulsed uniform recording magnetic field and TbFeCo media, the recorded mark length became much longer than designed one calculated by a linear velocity and a field pulse width, when the designed mark length was less than 100 nm. The mark elongation was more significant for the recording on a TM-rich medium (c=17.6). When the mark length was shorter than 40 nm, marks were not formed on a RE-rich medium (c=21.7) due to the collapse of domains. By introducing Gaussian profile of recording magnetic field with a maximum gradient of 10 Oe/nm together with the laser spot profile, the elongation of recorded marks was remarkably reduced. Furthermore, the stability of the marks shorter than 40 nm on the media c=21.7 was found to be improved. From the analysis of the effective field acting on the domain wall, it was found that the effect of the field gradient |∂H_c/∂χ|+|∂H_ext/∂χ| at the wall stable position was crucial to reduce the mark elongation as well as to improve stability of very short marks.

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The effect of thin Al underlayers for amorphous TbFeCo-based, perpendicular magnetic recording media were studied in a laser-assisted and also in a non-assisted, conventional magnetic recording method. With the insertion of only a few nanometers of Al underlayer underneath a TbFeCo layer, an increase of coercivity was observed and the linear recording density was improved. It is considered that the relatively rough, grain-like surface structure, of the Al underlayer worked as pinning sites for the TbFeCo laver.

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For a multi-level recording using magnetic field modulation, an exchange coupled film is applied. Therefore it is thought that the critical domain size r_c may be different from the r_c of a usual MO recording media. However, there is no research to theoretically analyze the r_c for multi-level recording using magnetic field modulation. In order to quantitatively analyze the change in r_c when changing each of the media constants in a quadri-value recording media, we modified Huth's model. It is clarified that an increase in saturation magnetization Ms, coercivity Hc, and a decrease in interfacial wall energy density σ _iw, is effective to make the _rc small

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With consideration to the Curie-Weiss law, we investigate magnetization reversal beyond the Curie temperature, from theoretical to experimental. This paper outlines a theoretical model in accordance with the Curie-Weiss law and also presents a new criterion for the shape stability of recorded domains using magneto-optical recording or hybrid recording. Fairly good agreement was obtained between the theoretical and experimental investigations.

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FePt (001) films with a variety of compositions were prepared on MgO (001) substrates by sputtering at reduced substrate temperature T_s of 300°C, and their magnetic properties, particularly the temperature dependence of magnetization were investigated. The film with a Pt-rich off-stoichiometric composition (Fe₃₈Pt₆₂) showed high chemical order and large perpendicular magnetic anisotropy, in contrast to the film with the stoichiometric composition showing poor chemical order. Besides the Curie temperature T_c for Fe₃₈Pt₆₂ showed no large change from that of the bulk ordered alloy with the same composition, however, was lower than that of the fully ordered bulk alloy with the stoichiometric composition. This implies that the films with Pt-rich offstoichiometric compositions have an advantage to thermally assisted magnetic recording which requires moderately low T_c.

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Granular-type FePt films with perpendicular magnetic anisotropy are obtained on top of Fe-Ta-C magnetic soft underlayer by annealing FePt/MgO multilayers. For high-density perpendicular magnetic recording medium application, the issues regarding the FePt film crystallographic texture, microstructure, chemical ordering and magnetic properties are addressed in this paper. Based on this medium design, double-layered FePt disks are fabricated on 2.5-inch glass discs. The magnetic recordin performances of these disks are evaluated by a spin-stand. The results reveal a close correlation between the disks SN_mR recording performance with the initial multilayer structure.

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The MsHc value of TbFeCo magneto-optical (MO) film has been identified as a key factor in high-density recording. A particular microstructure formed in the magneto-optical memory layer due to the magnetic underlayer was found to be effective for increasing the MsHc value in 160 nm thick TbFeCo recording film. However, a thinner memory layer is required for high performance of productivity
This paper describes the relationship between magnetic properties and the micro-columnar structure, which depends on the thickness of the TbFeCo recording film and its layer structure
It has been found that a thickness of more than 100 nm in the memory layer produced by sputtering from an alloy target is needed for the DWDD method. And there is some difficulty in recording a tiny mark on the 50 nm thick memory layer in a multi-layer MO medium
However, the static magnetic properties of the memory layer are not altered by differences in thickness. As much as 1.8 ×10⁶ erg/cm³ Ku can be obtained by sputtering a thickness of less than 80 nm from an alloy target, and it is possible to perform ultra-high density recording in an 80 nm thick memory layer with a mark length of less than 50 nm
These results suggest that control of the exchange coupling boundary between the layers in a multi-layer MO mediummakes it possible to record stable tiny marks.

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This project investigated the temperature dependence of the magnetization and anisotropy field of Fe-Pt nanoparticle samples with different order parameters and compositions. A decrease in the order parameter and/or deviation from equiatomic composition brings about a rapid reduction in the magnetization and anisotropy field with increasing temperature. The temperature dependence of the magnetic properties was found to be associated with the probability of Fe atoms being in Ll₀type atomic arrangement, which was obtained using Mossbauer spectroscopy, rather than with the order parameter. The changes in magnetization and anisotropy field correlated with each other and demonstrated a qualitative relationship in agreement with a theory based on magnetic thermal fluctuation.

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SmDyCo/Cr films have been prepared by an r.f magnetron sputtering system. The Cr underlayer was found to play an important role in increasing the coercivity (Hc) in the DyCo films because of the formation of granular structure. The effects of Dy substituted by Sm on the magnetic and magneto-optical properties of DyCo/Cr films have been investigated. By analyzing the figure of Ms*Hc vs. Sm concentration, optimum Sm concentration should be found between 16-22 at% to obtain maximum Ms*Hc. With increasing Sm concentration, the Ms is steadily increased, while the He is slightly decreased. With the increasing of Sm concentration, the reflectivity (R) and Kerr rotation angle (θA_k) are increased. It is believed that by choosing optimal sputtering conditions and suitable Sm substituting fraction, larger Ms and higher He can be obtained at room temperature for (Sm_xDy_1-x)₃₆Co₆₄ films.

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The multilayered FePt thin film structures have been fabricated. Silicon nitride films have been used as dielectric layer for sandwiching the FePt film. The Kerr rotation angle was affected by the composition of Pt concentration in the FePt layer and the FePt layer thickness. The maximum Kerr rotation angle was 0.82° for 10 nm Si₃N₄/Fe₃₅Pt₆₅/Si₃N₄/Al/Si structure. The variation of Kerr rotation with FePt thickness was also calculated by computer simulation.

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TbFeCo film is fabricated on isolated FePt grains to increase the domain wall coercivity (H_w) of TbFeCo film by exchange coupling effect between TbFeCo and FePt. The transition metal (TM) moment has a dominant charge in TbFeCo film ranging from room temperature (T_room) to Curie temperature. The FePt has average grain sizes such as 29.6, 16.6 and 7.0 nm in diameter, which are perpendicularly magnetized with a high coercivty (H_c), as high as 30-45 kOe at Troom. The TbFeCo/FePt composite film shows higher H_w, H_c, and M_sH_w than those of the single layer of TbFeCo film. We also estimate the amountof interfacial wall energy between TbFeCo and FePt.

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A systematic study of the magnetic and structuralproperties of Fe3Pt alloy thin films has been carried out. It is realized that the orientation of the Fe3Pt thin films can be controlled by choosing the different oriented substrate. The Fe₃Pt thin films are found to exhibit very large in-plane magnetic anisotropy. By changing the deposition temperature, one can tune the magnetic anisotropy constants of the films. The maximum value of magnetic anisotropy constants, K1 and K2 of Fe₃Pt films are obtained about -4×10⁶ and 2×10⁷erg/cc respectively, which are the new findings ever found for Fe₃Pt films. A close relationship is observed between the magnetic anisotropy constants and structural parameter. The magneto-optical properties of Fe₃Pt thin films are found similar to the bulk that is attributed to strong hybridization.

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The ion beam induced chemical vapor deposition (IBICVD) technique has been successfully used to fabricate Fe and FePt particles. Select area electron diffraction (SAED) patterns were used to study themicrostructure of the Fe and FePt particles. The as-deposited Fe and FePt particles are both amorphous. After being annealed at 600°C for 1 hour, the Fe particles remain amorphous, while the FePt particles are crystallized in fcc structure. The concentric magnetic domain structure has been observed in the as-deposited FePt particles, as revealed by the magnetic force microscopy (MFM) measurement. Measurements of cumulative magnetic properties of as-deposited FePt particles show coercivity of about 70 Oe.

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We improved the electron beam recorder with a differential pumping head for higher density discs andmass production. The beam diameters were improved by changing the aperture size of the objective lens, and beam stability was also improved by adding a sound proof case. As for the performance of the improved electron beam recorder, we have demonstrated the capability of 70Gb/in² density recording by an electron beam mastering process and readout by a solid-immersion lens with a blue LD of 405nm wavelength and 2.05NA.In addition, we improved the pit width uniformity by introducing an appropriatewrite strategy that was simulated by a Monte Carlo simulation to the recording pulses. Thus we were able to fabricate from a 104Gb/in² to 150Gb/in² ROM disc by using the write strategy. For the solid-immersion lens recording system with the blue LD and 1.84NA we obtained the clear eye patterns of 73Gb/in² in which the groove track pitch is 160nm by utilizing a phase change recording media and a polycarbonate substrate.

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The formation of ultra-high-density ferromagnetic column arrays beyond 1 Tera/inch² was investigatedusing porous alumina films formed on Si substrate. It was empirically known that a pitch of nanohole array shrunk with a reduction of anodic voltage. We carried out anodic oxidation of sputtered Al film at the anodic voltage below 10V, and found that the density of the nanohole arraysincreased significantly with a reduction of the anodic voltage.and reached 1.5 Tera/inch² when the anodic voltage was 5.0 V. We also succeeded in the electro-plating of Co column array in these fine holes.The Co column arrays formed by electroplating in the nanoholes were polycrystalline. and showed perpendicular magnetic anisotropy when their aspect ratio was larger than 3. The coercive field of Co columns tended to increase with a reduction of the hole diameter, which was confirmed by micromagnetic simulation based on the LLG equations. These results strongly suggest that ferromagnetic nano column arrays buried in porous alumina film on substrate have a high potential for application to a future ultra-high density magnetic recording media.

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We developed nanometer-order fabrication for 3-dimensional (3D) imprint molds, using acceleration-voltage-modulation electron beam (EB) direct writing. The inorganic EB resist was spin-on-glass (SOG), whose depth was controlled by changing the EB acceleration voltage. After EB exposure, the sample was developed using buffered hydrofluoric acid. The fabricated pattern depths on SOG were well gradated, and the depth resolution was 20 nm per 100V. The width resolution was 40 nm on SOG using an electron beam with a diameter of a few nanometers. Patterns were transferred by pressing the fabricated 3D SOG mold to a photo-curable resin under a pressure of 0.5 MPa and curing it with a 1 J/cm² ultraviolet dose. Replicated patterns showed faithful, defect-free multigradation. Using SOG as the material for an ion beam etching mask, 3D molds were fabricated from diamond, engineering plastic, and quartz.

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Regularly aligned array structures of square and cross-shaped magnetic dots of sub-micrometer size an in silicon wafers were fabricated. It was found from magnetic force microscope observation that the spin vortices of adjacent square dots showed opposite chirality to each other, probably due to magnetostatic interaction. In the cross-shaped dot arrays, magnetic poles appeared at the end of each bar and a complicated contrast was seen at the crossing point. These observations are successfully explained by a three-dimensional micromagnetic calculation using the Landau-Lifshitz-Gilbert equation.

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In the optical drive system adopting optical flying-type head (OFH), flying stability of small OFH interfaced with a removable plastic disk is investigated as basic functions of reliable optical pickup head for first surface recording. Additional micro actuators for focus servo are studied for better interface of OFH on the thin cover layered plastic disk to eliminate focus error due to the non-uniformity in cover layer thickness and the tolerance of lens assembly.

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One of the trends on information storage device is focused on the development of small form factor optical disk drives with Optical Flying Head (OFH). Many different types of sliders for OFH and optical component systems have been introduced in the literature. However, the research about the actuating system is not much in the literature. In order for a slider with OFH to be successfully implemented in the system, a suspension is needed to be properly designed. Generally, a suspension supports slider performance, and tracking servo capacity in HDD. As the suspension supported the OFH slider which has larger mass and objective lens, it is required to satisfy shock performances for the mobility, and it also should meet the optical characteristics. In this study, the suspension for small form factor ODD is designed with sensitivity analysis. The dynamic characteristics of the suspension with OFH are analyzed finite element method and experiment, and the flying height and its variation of the OFH slider is measured by laser doppler vibrometer.

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We studied on enhanced photon-tunneling and the near-field enhancement effect for a nano-scale aperture with a concentric surface plasmon resonance structure. About two-orders larger light transmission and an enhanced near-field were achieved by optimizing the grating structures. This enhanced near -field was applied to optical recording, and about 100 -nm recorded patterns were successfully made on phase change media. This surface plasmon optics would open up the ultra-high-density recording technology.

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We present three-dimensional optical memory using multilayered media. Multilayered media provides higher contrast readout and higher recording density. We analyzed optimum thicknesses in the multilayered medium for a readout system of the memory. We also demonstrated bit data recording and reading in the multilayered medium at high recording density.

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Using a compound optical element with three polarized holograms, a phase compensation film, and a grating for PS-DPP (Phase-Shift Differential Push-Pull) method, we have developed a miniaturized integrated optical pickup for Mini Disc Player, and it got free of the tracking adjustment by rotating the integrated unit. The jitter of the MO (Magneto-Optical) signal reproduced by this pickup reached 9%.

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This review describes the magnetization-induced second harmonic generation (MSHG) in (Fe^II_xCr^II_1-x)1.5[Cr^III(CN)₆]·E 7.5H₂O. The polarization of SH light of the (Fe^II_xCr^II_1-x) 1.5 [Cr^III(CN)₆]·7.5H₂O films was rotated by an applied external magnetic field. The observed SH rotation angle of 1.3® was much larger than the Faraday rotation angle of 0.079® at 388 nm. This SH rotation is ascribed to the interaction between the electric polarization along the out-of-plane of film and spontaneous magnetization. The magnetic linear term (χ_ijkL^magn(1))contributed particularly to the SH rotation.

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Strong optical second-harmonic was observed in a centrosymmetric LCMO thin films in ferromagnetic phase and assigned a s magnetization-induced effect. B y n on-linearopticalexperiment, magnetization is shown to be sensitivefor laser illumination. A threshold of photoinduced demagnetisation depends on the films structure: it isdrastically decreases in the presence of grain boundaries. For steady state conditions, the SHG field is described bypower law with critical exponent 2β=0.64±0.05. Abovethe threshold a complicated dynamics of photoinduceddemagnetization is observed, which is modeled byphotoinduced modification of electron phase separation.

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Magneto-optical microscope utilizing polarization modulation technique was developed to obtain magnetooptical (MO) images involving quantities of MO effects, such as Faraday rotation and ellipticity. Faraday rotation images were calculated 'from three images taken with a linear polarized light and circularly polarized lights with left and right rotation. Square dots pattern of Y₂BiFe₄GaO₁₂ film with a dimension of 50μm × 50μm and a thickness of 200 nm were measured as a sample, and the magnetic contrast was clearly observed in images of both Faraday rotation and ellipticity at wavelength. The quantitative value of the Faraday rotation and the ellipticity were measured to be 0.5° and 0.15°, respectively. Resolution of the Faraday image was obtained to be less than 0.05° by taking an integration of images and a smoothing treatment.

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Spectroscopic ellipsometry, reflectometry and magnetooptical (MO) spectroscopy in the zero and first diffraction orders are used to analyze submicron ultrathin MO gratings. Two different theoretical approaches, a rigorous analysis and an approximate method, are used to simulate the optical and MO response of the gratings. The numerical analysis suggests the presence of native oxide layers on the substrate and capping. A strong spectral anomaly observed in the MO response is identified by the integration of both theoretical approaches. The possibility to monitor the quality and topography of shallow gratings with high sensitivity is concluded.

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We fabricated one-dimensional magnetophotonic crystals (1-D MPCs, hereafter) with single-cavity structures of (Ta₂O₅/SiO₂) ^k/Bi: YIG/(SiO₂/Ta₂O₅) ^k (k=2, 6). Their fundamental optical and magneto-optical fundamental properties were investigated in detail. We obtained experimental results that were in good agreement with the theoretical predictions: the Faraday rotation angle of the medium was more than 100 times larger than that of a Bi: YIG single-layer film. In addition, we performed numerical calculations by taking the optical dissipation effect into account, and the experimental results were examined. The optical dissipation was found to be a key parameter in determining the performance of 1-D MPCs apparatus. The Bi: YIG and dielectric films were deposited under the preparation conditions shown in Tables 1 and 2. The design wavelength was 720nm. Optical and magneto-optical properties of the prepared 1-D MPCs were calculated theoretically by solving Maxwell's equations with the bigyrotropic dielectric tensor for the magnetic layers under the electromagnetic boundary conditions imposed at all discontinuous planes. This is usually rather tedious, but is easily achieved by means of the matrix approach.

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We have investigated an influence of magnetic materials embedded into opal lattices on transmissivity of three-dimensional magnetophotonic crystals. It was shown that increase of volume fraction of magnetite in the opal lattice leads to a dramatic decrease of transmitted light intensity in the visible region. Opal-dysprosium gallium garnet composites exhibit a broadening and shifting of the (111) photonic band gap with an increase of volume fraction of garnet. We also found considerable changes in the Faraday rotation inside the (111) photonic bandgap of an opal-magnetite magnetophotonic crystal. visible light: they can diffract light selectively in three-dimensional space and split a light beam into several beams. In comparison with known three-dimensional photonic crystals, we consider three-dimensional MPCs as more effective because their photonic properties are sensitive to magnetic and electric fields and they have the potential for use in a variety of optoelectronic devices.

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Molecular beam epitaxy grown Au/Fe (t)/Au, Au/Fe/Au (t)/Fe/Au and Ag/Fe (t)/Ag sandwiches on MgO (001) substrates were investigated by means of classical and magneto-optic (MO) Kerr ellipsometry and relative reflectance spectroscopy at photon energies between 1.5 and 6 eV. The layer thickness t varied between 1.0 and 2.5nm for Au spacer and between 0.8 and 1.8nm for Fe. The MO polar and longitudinal Kerr effect spectra in Ag/Fe (t)/Ag can be explained using a single off-diagonal permittivity tensor element. This is not the case in Au/Fe (t)/Au, Au/Fe/Au (t)/Fe/Au. Deviations of the longitudinal spectra from the model indicate the anisotropy in the permittivity tensor and are assigned to an Fe-Au interface layer of reduced symmetry. The interface effect, observed between 3 and 4.2 eV, is best resolved in Au/Fe/Au (t)/Fe/Au, but can also be seen on Au/Fe (t)/Au. The relative reflectance spectra in Au/Fe/Au (t)/Fe/Au with an Au reference reflector show a narrowing of the Au peak centered at the photon energy of 3.5 eV. It is proposed that the narrowing is induced by adjacent Fe layer with in-plane magnetization.

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Reflectivity and magneto-optical Kerr spectra are measured in epitaxial FePt films prepared under reduced substrate temperatures. From these spectra off-diagonal elements of conductivity tensor was calculated. By comparison with those prepared under conventional preparation conditions, the Ll₀-ordered FePt films prepared at reduced temperatures proved to have similar electronic properties to those prepared at elevated temperatures. It is also elucidated that disordered FePt films prepared at 300°C show intermediate electronic states between ordered and disordered states.

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There are two parts in MOKE hysteresis loops, typical for materials with perpendicular magnetic anisotropy. One is due to a steeply falling edge or rising edge accompanied by the sign changes in magneto-optical Kerr effect (MOKE) signal. The other corresponds to a slow change of non-transition segment. A satisfying tradeoff between response to rapid change and noise rejection in non-transition segment of the loop is hardly obtained. The problem may be solved using a method based on non-uniform sampling. Its goals are to reduce distortion of the transitional waveform and noise, to obtain high resolution of transitional waveform and to decrease the number of sampling points. This paper describes the principle of non-uniform sampling and its implementation, and we designed a comparative experiment using a constant sampling frequency and multi-sampling frequency. The result shows that the measurement system with non-uniform sampling can reduce distortion of the MOKE loops, improve the accuracy of the coercivity, and decrease the number of sampling points.

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The magnetic properties of 1μ;m wide Co zigzag wires are studied by the in-situ combination of magnetic force microscopy (MFM) and magnetoresistance (MR) measurements. The main advantage of our room temperature experiments is the possibility to directly link changes in the magnetization to changes in the magnetoresistance. In order to support the interpretation of our experimental results, the magnetic states of the zigzag wires are obtained from detailed micromagnetic simulations. The magnetic properties of the zigzag wires are dominated by the shape anisotropy due to the reduced width, while the observed magnetoresistance is largely determined by the anisotropic magnetoresistance (AMR) effect.

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The transfer ratio and magneto current were investigated for magnetic tunnel transistors (MTTs) with two different emitter tunnel junctions. The tunnel resistance-area products were 4×10⁵ (Sample A) and 12×10⁵Ωμm² (Sample B). The transfer ratio of Sample B was approximately 1.3×10^-4 at the emitter voltage of 1.0V, whereas that of Sample B was approximately 0.5×10^-4. The maximum magneto currents of Sample A and B were approximately 300% and 200%, respectively. These results indicate that the transfer ratio and the magneto current depend on the tunnel resistance of the AlO_χ layer.

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(Cr_1-χV_χ) Pt₃ alloy films were obtained by annealing (Cr-V)/Pt multilayer films prepared by rf magnetron sputtering. The structure and magnetic and magnetooptical properties for the alloy films were investigated. The CrPt₃ (χ=0) film exhibited an uniaxial anisotropy of K_u=2.4×10⁶ erg/cc and a saturation magnetization of M_s=235 emu/cc. The saturation magnetization and the uniaxial anisotropy decreased with increasing V substitution χ. On the other hand, variations of the Kerr spectral shape with increasing substitution χ were observed. The θ K peak around 1eV of the CrPt₃ film shifted lower energy side with increasing χ, and the (Cr_0.37V_0.63) Pt₃ alloy film showed a plateau around 2 eV in the Kerr spectrum. TheΧ-ray magnetic circular dichroism taken in the V 2p-3d excitation region indicated that the V has a ferromagnetic moment and align parallel to the Cr moment.

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When measuring the domain shrinking velocity of GdFeCo single layer film, which is an expanding layer of Magnetic AMplifying MO System (MAMMOS), scattering was seen in the shrinking velocity when the effective driving field was over 100 Oe. Walker's limit was thought of as the cause of the scattering, and then the damping constant was determined to be 0.29. When the in-plane field was applied, the scattering disappeared, and an increase in shrinking velocity was seen.

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Optical second-harmonic generation (SHG) of purely magnetic origin has been observed in thin films of Lu₃-_χ Bi_χ Fe_5-y Ga_y O₁₂ grown on (100) oriented gadolinium gallium garnet (GGG) substrates for the purpose of magneto-optical imaging. The films have in-plane magnetization, and when studied in transmission at normal incidence all relevant elements of the crystallographic part of the second order non-linear optical susceptibility tensor vanish identically, while a magnetization-induced contribution remains. The observed rotational anisotropy SHG signal in a transverse magnetic field is demonstrated to be indeed of purely magnetic origin, and can be switched off by applying a polar magnetic field.

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We present results of a time-resolved study of the ultrafast magnetic response of Gd_23.1Fe_71.9Co_5.0 MAMMOS structures under conditions near actual read/write temperatures. An all-optical pump and probe method was used in which an intense (pump) light beam excited a medium due to ultrafast laser heating and a less intense (probe) beam monitored this photo-excited state through the magneto-optical Kerr effect. Our experiment clearly demonstrates that the photo-excitation effectively excites coherent spin waves in the magnetic material. Precession frequencies of several GHz and relaxation times in the nanosecond range were observed.

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The electronic and spin states of the perpendicular magnetization films of Tb₁₇ Fe_χ Co (83-χ_) (χ=0, 9.5, 32.5, 61.4 and 74.5) were measured by means of soft Χ-ray absorption and magnetic circular dichroism spectroscopy for Tb element to investigate the magnetic anisotropy. The origin of the magnetic anisotropy is said to be caused by a large orbital moment of the well-localized 4ƒ electron. The expectation values of orbital moment <L_z> for the different composition of Fe were estimated to be about 1.2 μ_B applying a sum rule for the spectra. Using a theoretical model calculation the opening angle of the conical distribution of Tb moment along the easy axis of magnetization was estimated to be about 67 degree.

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In rapid progress of fiber-optic communication systems, variable optical devices are required. This paper reports recent trends of variable optical attenuators, tilt equalizers and optical switches, based on the Faraday effect. Progress of fast response in variable optical attenuators is also described.

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A short review on optical switches with emphasis on magnetooptical methods is presented. A novel magnetooptical switch of latching type with an yttrium orthoferrite optical rotator is described. The crystal remains in a given magnetic state for unlimited duration without energy supply. The response time is about 30 ns, the aperture of the optical rotator is 350μm.

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Graded-index clad layers with different thickness were used to increase the magneto-optical TE-TM mode conversion efficiency in Cd_1-χMn_χ Te waveguide. Almost complete mode conversion efficiency of 98%± 2% was achieved for the waveguide with 4000-5000 Å thick graded layer at λ=740nm and H=5.5kG. The high mode conversion efficiency is due to the strong reduction of the phase mismatch between TE and TM modes. The waveguide also showed low optical loss below 1 dB/cm, high magneto-optical figure-of-merit above 500 deg/dB/kG and an isolation ratio of 18 dB at λ=740nm. Highly efficient present Cd_1-χMn_χ Te waveguide demonstrates the feasibility of monolithical integration of an optical isolator with semiconductor optoelectronic devices.

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