The growing acceptance of optical storage in the marketplace is intimately tied to the applications that it serves. By exploiting the unique attributes of this technology, the enormous amount of information that is now stored on paper and film can be managed in an efficient and cost-effective manner.

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  Pt/Co and Pd/Co multilayers with a large perpendicular magnetic anisotropy and a relatively large polar Kerr effect at short wavelength are considered candidates for a new, high density, magneto-optical recording medium. Their potential application has motivated numerous studies of their fundamental magnetic, magneto-optical, and practical recording properties. This paper reviews the current state of understanding and some of the challenges that need to be met before practical application of this multilayer technology.

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  Macroscopic ferrimagnets have been prepared by codepositing Co, Tb and Eu₂O₃ by e-beam evaporation. The films show compensation temperatures at compositions which indicate that the europium is in the divalent state and is coupled antiparallel to the Co magnetization. Under the present conditions of deposition, these films do not show perpendicular easy axis anisotropy, whereas previously studied Co-EuS films did. At room temperature there is magneto-optical evidence that the EuO precipitate phase is coupled antiparallel to the cobalt. That is, a film with 80 mole % Co (in the Co dominated composition range) shows a positive peak in the Kerr spectrum at 1.7 eV, whereas a Tb doped EuO film shows a negative peak in the same energy range. The change of sign of the Kerr peak shows that the EuO phase is coupled antiparallel to the cobalt.

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  MnSbPt films (thickness of 1000Å) with the concentration of 50at%Mn. 44at%Sb and 6at%Pt annealed 300°C showed giant Kerr rotation angle of about 0.9° at short wavelength of λ=500nm. The results of structural analysis with X-ray and NMR revealed that the giant Kerr rotation angle observed in present films is closely related to the MnSb compound including Pt atom in NiAs structure. The experiments using powder alignment samples prepared under external magnetic field showed that the direction of the easy axis of magnetization of present MnSbPt with NiAs structure was found to change from c-plane to c-axis with increasing Pt concentration.

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  Relations between surface roughness on the Bi layers and Bi deposition conditions on various substrates were investigated. On flat glass substrates, lower deposition rate and higher substrate temperature reduces the number of hillocks and surface roughness on Bi layers, and increases the degree of c-axis orientation. Bi layers on the grooved substrate with optimized deposition conditions have many large size hillocks (hundreds of nm order) at boundaries between lands and grooves. The two step deposition process for the Bi layer was newly developed to reduce the growth rate of hillocks. No hillock appears on the Bi layers at the land-groove boundaries when using this process. The noise reduction of 7 dB can be achieved by the two step deposition process for the Bi layer.

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  The garnet film with a nanometer-scale grain exhibits high recording characteristics. The memory layer of a high-Bi content garnet with 50nm grains was obtained by crystallizing the amorphous film formed on a low-Bi garnet underlayer. The media noise of the bilayer was decreased by applying a non-magnetic garnet for the underlayer and flattening it by sputter-etching. We have prepared a fine-grain bilayer garnet film on a 130mm glass disk with a groove and obtained a carrier-to-noise ratio of 42dB(0.47μm mark length) at a wavelength of 488nm. Small marks of 0.38μm were successfully recorded on the disk.

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  Recent observations of irregular stripe domains in demagnetized thin CoPd multilayers and the comparison of measured domain sizes with theoretical models are reviewed. The models are discussed in terms of deviations from models of 'equivalent uniform' films, which appear to be small for wide domains (relative to film thiekness). Theoretical estimates of significant domain wall energy reduction due to magnetostatic effects, based on micromagnetic simulation, are reported but so far not confirmed experimentally.

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  General mean-field theory for magnetic phase transitions in layered structures is formulated. The spin-reorientation transition is addressed for the single-film and double-film systems. The competition between different anisotropies through the exchange coupling is analyzed. The Curie temperature in ferromagnetic superlattice is derived and its dependence on the sublattice thickness is discussed.

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  The screened charge model, which is a metallic analogue to the non-metallic point-charge model, is used to investigate the 4f anisostropy in rare-earth-containing metallic multilayers. The crystal-field parameters A_m⁰ are predicted to exhibit a mindependent exp(-qz) dependence on the distance z from the neighbouring layer and the Thomas-Fermi screening parameter q. An estimated upper limit of the surface anisotropy which can be found in these structures is 20 mJ/m² (20 erg/cm²).

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  Intermediate layers of exchange-coupled Gd-Fe/M/Tb-Fe (M=Dy-Fe, Al, Pt) triple-layered films are investigated in detail. Measurements of interface wall energy and magnetic moment of the intermediate layer reveal the mechanism of exchange-coupling in triple-layered films. For the Dy-Fe intermediate layer, the reason for the exchange-coupling is considered an ordering of magnetic moments in the Dy-Fe layer by molecular field from adjacent layers. On the other hand, the exchange force from the Tb-Fe layer to the Gd-Fe layer would pass through pin hole and/or atomic diffusion for the Al intermediate layer. The exchange-coupling for the Pt intermediate layer is explained by the polarization of Pt moment and/or the RKKY interaction.

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  In an earlier paper we have reported about prelimary results of evaporated CoNi/Pt multilayers [1] The main result at that time was a substantially lower Curie temperature for a Co₆₀Ni₄₀/Pt multilayer in comparison with the known Co/Pt having the same magnetic parameters. A study of the bulk magnetic phase diagrams shows a lowered T_c for adding Ni into Co. The problem by tailoring the composition for the T_c is that one also have to consider the Kerr rotation because this value scales with the magnetic moment of the multilayer.

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  Ubiquitous access to large quantities of information content is one of the main benefits anticipated from the emerging global interconnection of computer networks. One of several major factors in achieving this objective is the cost and performance of the distributed storage systems which will act as the repositories for the information. This article presents an overview of the architecture, major components and requirements for storage systems which can support distributed storage intensive applications.

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  A new single-disk sputtering system for the production of magneto-optical disks is presented. It features 7 process stations for multi-step static deposition which are arranged vertically on a circular path, and which can be equipped with cathodes or an etching station according to the specific needs. Special emphasis is put on the design of the cathodes being completely axialsymmetric in geometry and the sputter gas management. Results from DC-reactive sputtering for fast deposition of dielectric layers are presented with layer uniformities of ± 2.0 %.

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  Chemical bonding state and protective properties of nitrogen defective off-stoichiometric silicon nitride (SiNx) films for magneto-optical disks were investigated with X-ray photo spectroscopy. Both refractive index and extinction coefficient increase with decreasing gas flow ratio of N₂ to Ar. Changes in the optical constants of SiNx with decreasing nitrogen content are caused by (1) an increase of Si clusters and (2) a change on tetrahedral sites of Si from Si-N₄ to Si substitutional Si-N_4-xSi_x. An aging test (80°C, 90%RH) was carried out for a magneto-optical disk with SiNx protective layers. C/N ratio and reflectivity remained constant up to 1000 hours. The SiNx film is sufficient for use as a protective layer in magneto-optical disks.

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  Recently, a target material having a low magnetic permeability which is suitable for magnetron sputtering is required. In a Tb-Fe-Co composite type target, it has been found that by substituting Fe-Tb alloy phase for pure-Fe phase, the maximum magnetic permeability μmax can be reduced from 27 to 8 or less. And the uniformity of Tb distribution in a film can be kept by using a “Tb-Fe eutectic alloy (αTb + Fe₂Tb)” as a source of Tb content. Furthermore, in a Tb-Fe-Co-Cr system, by substituting Co-Cr alloy phase for pure-Co phase, μmax can be reduced to 5. It has been also confirmed that the reduction of the magnetic permeability is quite effective for the improvement of the utilization efficiency of the target material.

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  The mechanisms of magnetization reversal and the origin of coercivity are determined for ultrathin ferromagnetic Co-films with perpendicular anisotropy. Analyzing the field dependence of the domain wall velocity and the thickness dependence of the coercive field H_c at low temperature. we concluded that the domain wall pinning at the steps limiting the atomically flat terraces of the Co-film is at the origin of the coercivity. The temperature dependence of H_c for different Co-film thicknesses is related to that of the propagation field and to dynamical effects.

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  The majority of rare earth/transition metal (RE-TM) magneto-optical (MO) materials are made by a sputtering process. The coercive force Hc depends very much not only on the composition but calculations have shown that it will depend also upon the size and number of voids. In this paper, we report on the effects of argon pressure on the value of Hc, on the numbers and sizes of voids, and on the values of the gap densities in the coatings with columnar structures. The numbers and sizes of the voids were determined by using small angle x-ray scattering (SAXS) measurements. The gap densities were measured by a new method using TEM. We have also determined the position of these voids using TEM. According to measurements from a vibrating sample magnetometer (VSM), SAXS, and TEM, it was found that there is a significant contribution to the increase of Hc with coating pressure by the increasing volume fraction of these voids located mainly in the gaps between the columns of the MO films.

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  Magnetization reversal in amorphous TbFeCo films on patterned glass substrates was studied. Two types of patterns were examined: grooves and square patches. Pinning of the domain walls at the side-walls of the patterns was observed. The pinning depends on the depth of the patterns and the angle of the side-walls: greater depth and steeper side-wall produce stronger pinning. Thermomagnetic recording experiments confirm the ability of patterned substrates to confine recorded domains within boundaries defined by the side-walls.

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  The magnetic integrated head described in this paper can modulate at high frequency a magnetic field for direct overwrite applications in magneto-optical recording. It has been produced on silicon substrate and its small size allows a low cost mass production. The protective layer has been grooved in order to obtain a high flying height of about 4 μm allowing dusty environment. Fabrication of prototypes and tests have been carried out at LETI and the first results are presented. This head should be useful for future high density magneto-optical recording with magnetic field modulation.

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  Plasma etching treatment of SiN underlayer was performed to enhance the magnetic sensitivity of TbFeCoCr magnetic-optic disc which facilitates the magnetic-field-modulation direct overwriting behavior. The effect of plasma etching on the interfacial structure was investigated by high-resolution electron microscopy and stress measurements. The ordered structure at the interface between SiN underlayer and MO Layer was observed for samples with highly etched underlayer. Compressive residual stress was induced by the plasma etching of SiN underlayer. The results suggest that the magnetic sensitivity is improved by less pinning sites and the lower domain wall energy density at the interface.

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  The addition of the magnetic capping layer on the TbFeCo recording layer is effective for improvement in the field sensitivity of MO media. We newly found that a cobalt film works as the capping layer in the case of very thin film with thickness of 0.3-0.5 nm. The ultrathin cobalt capping layer is favorable for media production from the viewpoint of cost and through put of the sputtering process. It is supposed that the change in the magnetic properties of cobalt films with reducing the thickness, such as the decrease of the saturation magnetization, causes the capping layer effect.

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  TbFeCo magneto-optical single layer disks with different compositions have been investigated for recording of small size domains. Using a 830 nm wavelength laser, circular shaped domains with a diameter of 0.25 μm diameter could successfully be written. A low writing stability, dependent on the applied field, was found when recording domains smaller than 0.5 μm on a transition metal rich disk. On the contrary, a high writing stability was achieved on a disk with a highly rare earth rich composition. On this disk two 0.25 μm domains could succesfully be written as close as 0.1 μm to each other. It was also possible to use this single layer TbFeCo disk for recording of domains with widths of 0.1 μm.

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  The application of scanning laser microscopy to the characterisation of magneto-optic storage materials and to the evaluation of the performance of magneto-optic recording systems is described. Fundamental material properties such as Kerr rotation, reflectivity, coercivity and hysteresis loop shape are obtained, on a microscopic scale, for a variety of magneto-optic recording films. The recording behaviour of films is also investigated, and realistic, in-situ, annealing studies are performed to assess their long term stability. Optical system evaluation in terms of impulse response, step response, optical resolution and modulation transfer function is also carried out. Novel readout methods such as edge detection, confocal detection and super-resolution are investigated.

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  For advanced semiconductor lasers, the maximum output power as well as the lifetime is limited by localized facet heating leading to mirror degradation and the occurrence of catastrophic optical damage (COD). The measurement of the laser facet temperature rise behavior, however, is a difficult task because of the small dimension of the lasing region. Utilizing microprobe Raman spectroscopy, we were able to systematically study the laser facet heating behavior with good temperature sensitivity and sub-micron spatial resolution. From these temperature rise data, wc have gained a better understanding of the physics and chemistry of laser diode facet degradation and the mechanisms leading to COD. The relationship of facet temperature to maximum laser output power and lifetime is discussed.

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  The imaging principle of spin polarized low energy electron microscopy (SPLEEM) is describes. Correlation of magnetic and microstuctural properties is demonstrated in investigations of Co ultrathin films on epitaxial Au layers on the W(110) surface. Interface steps are seen to have a dramatic influence upon magnetic domain structures. Crossover from out-of-plane to in-plane magnetization with increasing Co thickness is also related to magnetic anisotropy.

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  An introduction to magnetic force microscopy (MFM) is presented which provides the information necessary to make simple interpretations of MFM images. Images of bits written on standard 1X format magneto-optic (MO) disks (sold commercially) are shown and discussed qualitatively. When the MFM tip is close to the surface of the magnetic film (reflector coating removed), the near field is detected such that the transition between oppositely magnetized regions can be seen. At greater distances where only the far field is sensed, the bits can be imaged, but the edges are not resolved. This work shows that for highest resolution MFM imaging of the bit edges, the reflector coating must be removed.

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  Formation of small magnetic domains has been studied using a local tunneling current in the scanning tunneling microscope(STM) for the Co/Pt multilayered magnetic film with perpendicular magnetization. Calculation of thermal diffusion equation suggested that a heated area higher than the Curie temperature of the magnetic film could be focalized on the area less than 100 nm in diameter by the current heating. In experiment, applying a pulsed voltage between the STM tip and the sample, the magnetization switching has been confirmed without an assisted external field and the magnetic domains of 200 nm in diameter have been observed using a polarized optical microscope. The domain formation through the magnetization switching is considered to be due to the demagnetization effect of the neighboring domains. It indicates that the method has a potential to realize a new data strage technique with ultrahigh densities.

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  We have prepared CO_xNi_1-x /Pt multilayers by evaporation under UHV conditions and studied their magnetic and magneto-optical properties. By adjusting the Co content it is possible to tailor the Curie temperature (T_C) for magneto-optical storage application without trading off the other useful characteristics. For instance for x=0.3, for magnetic layers of the order of 5 Å one has a rectangular M-H loop with coercivity as high as 1.4 kOe with a polar Kerr rotation peak of 0.3 deg at the photon energy of 4 eV and a T_C = 180°C. For x=0.5, one has similar properties but with a T_C of 200°C. These materials hold very good promise for high density magneto-optical recording in the blue light.

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  Pt/Co films with thicker Co bottom and top layers improve the magnetic sensitivity of Pt/Co multilayer disks. By increasing the Co bottom and top layer thickness into 7Å in Pt8Å/Co3Å disks, the magnetic sensitivity is improved to an erasing field of -150 Oe and a writing field of 150 Oe, whereas in a conventional disk an erasing field of more than -400 Oe and a writing field of 300 Oe are needed. Carrier level increases because the total Co thickness is larger. Therefore, compared with a conventional Pt/Co disk, 1 dB higher carrier to noise ratio is obtained. Improved Pt/Co disks using thicker Co layers are promising candidates for high density magneto-optical disks using a short wavelength laser and a magnetic field modulation method.

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  The dependence of microstructure and magnetic properties of Co/Pt multilayers sputtered on sputter-etched Si nitride underlayers were systematically investigated under varied conditions, The microstructure was determined using x-ray scattering and cross-sectional high-resolution electron microscopy. It was found that the characteristics of the underlayer surface and consequently the microstructure and magnetic properties of the multilayers are sensitive functions of the sputter-etching conditions. Uniaxial perpendicular anisotropy was found to initially increase as the underlayer was made smoother by sputter-etching, due to stronger interface anisotropy. However, with longer sputter-etching times and extremely smooth underlayers, it was found that the anisotropy peaks and decreases because there is a concomitant reduction in grain size which reduces the volume anisotropy. Coercivity was the largest for slightly etched samples. Static domain writing tests suggest that the multilayers deposited on etched underlayers have improved thermal conductivity.

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  Co/Pt multilayers were evaporated in one batch on substrates at room temperature, which were precoated with Ga₂O₃ and ZuO underlayers of various thickness. The column size of the multilayers was found increase with the thickness of underlayers. The coercivity measured from Kerr magneto-optic loops of Co/Pt multilayers increases with the column size until it reaches the maximum, ∼900 Oe, at size ∼700Å, then decreases with column size. A model of magnetically independent columnar particles was assumed to correlate the measured coercivtiy and column size. The values of saturated magnetization, Ms and anisotropic energy, K, calculated by this model are 378 emu/cm³ and 1.66x10⁵ erg/cm³, respectively.

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  Magnetic and magneto-optical(MO) properties are investigated for Nd(Tb,Dy)/FeCo multilayers(MLs) prepared by rf magnetron sputtering method. Perpendicularly magnetized films with good square hystereses loops and reasonably large Kerr rotation θ_K at shorter wavelength, are obtained by adjusting the composition as well as the bilayer period. In this work the maximum perpendicular anisortropy K_u of 50x10⁴J/m³ and the maximum θ_K of 0.33deg. are obtained for Nd₆₅Tb₃₅/Fe₈₁Co₁₁ and Nd₆₇Dy₃₃/Fe₈₁Co₁₁ MLs with the bilayer period of 1nm and the bilayer thickness ratio of 1.

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  The exchange coupling between a planar GdFeCo and a perpendicular anisotropy DyFeCo amorphous films has a strong influence on the magnetization processes of the bilayer as investigated in the present work from both experimental and theoretical analysis. From appropriate choice of the sputtering parameters during deposition of the bilayers we have adjusted the composition of each layer which gave the possibility to well separate their compensation temperature and simplify the investigation of the temperature dependence of the hysteresis diagrams of the coupled bilayers as observed from Faraday rotation measurements. The exchange coupling between the in-plane and perpendicular magnetization GdFeCo and DyFeCo layers has been investigated from the different perpendicular saturation fields observed in the GdFeCo single layer and in the GdFeCo/DyFeCo bilayer. A capping field produced by the exchange coupling induces strong modifications of the hysteresis in both planar and perpendicular layers which have been calculated from the total free energy of the coupled system and compared to experiment.

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  PrGd/FeCo multilayers prepared by the rf sputtering method exhibit perpendicular magnetic anisotropy Ku enhanced by the multilayer (ML) structure. The largest value of Ku obtained is about 30×10⁴ J/m³ at a bilayer period of 1 nm with Pr composition at around 35at. % in rare earth layers and Co composition at 10at. % in transition metal layers. The figure of merits of magneto-optical effect, is 20 to 30% larger than conventional TbFeCo films at the wavelength of 400nm. From the analysis of low angle X-ray diffraction, the relationship between the enhanced anisotropy and the ML structure is discussed.

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  The multilayer amorphous GdCo films were prepared by diode and triode r.f. sputtering method. The compositions of the layers were determined by a magnetic compensation temperature (T_comp) with use of torque method. T_comp was found by the dependence torque moment as a function temperature L(T). The minimums of this function were connected by T_comp. The magnetization reversal processes were studied by use of Hall effect and magnetoresistance (MR) methods. The hysteresis loops of anomalous Hall effect and magnetoresistance have three satellites loops besides of the band loop. The observed anomalous hysteresis loops of Hall effect and MR are discussed in terms double layers' model with use the H-T diagram of the magnetic state.

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  Well oriented CoTi-substituted Ba-ferrite thin films, with c-axis perpendicular to the film plane, have been produced by pulsed laser deposition on (0001) sapphire substrates at 840 °C. These films were of good optical quality and exhibited optical and magneto-optical properties similar to the bulk single crystal material. Furthermore, angular thickness variations caused by narrow plume distributions were studied by depositing onto glass substrates and correlating variations in reflectance with thickness variations through optical interference effects. The surface morphology of the ceramic Ba-ferrite targets after progressive laser illumination was studied by scanning electron microscopy.

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  For the purpose of reducing the media noise N_n of garnet films for magneto-optical recording, we investigated the technique to increase the stress induced perpendicular uniaxial anisotropy energy K_λ by stacking the garnet film with the stressed overlayer. K_λ of the garnet film was increased from 1.4×10⁴ to 2.2×10⁴ erg/cm³ by stacking with the stressed reflective Al-Tl overlayer. This effect leads the decrease in N_n and the increase in the carrier to noise ratio (CNR). As a consequence, CNR =55∼56 dB was achieved.

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  Bi which precipitates near the surface of as-deposited film is the origin of surface roughness of Bi-substituted garnet film. The Bi-rich thin layer can be effectively removed from the film surface by successively sputter-etching a film after deposition for a period equal to 1/12 of sputtering time. The averaged surface roughness of garnet film crystallized from this state is improved by up to 1/4 compared that of the non-etched sample. Regular shaped bits can be recorded on the garnet bi-layered medium each layer of which was processed using this method.

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  Garnet fine particles are prepared by coprecipitation and annealing. The saturation magnetization of the particles increases as the annealing temperature increases. Almost all X-ray diffraction peaks from the particles annealed at 700°C for 1h are assigned to garnet. Faraday rotation of the particles which are dispersed into methylene jodide is measured under a polarization microscope. The Faraday rotation of the coated films are shown as a function of wavelength. Existence of small fine particles of about 50nm diameter is confirmed in the coated film by SEM observation. A magnetic field pattern was displayed using the coated film prepared.

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  A soft-spin Heisenberg model is used to investigate the Curie temperature of elementary iron and iron-rich intermetallics such as Sm₂Fe₁₇. In the localized limit the mean-field solution of the classical Heisenberg model is reproduced, while quasi-localized perturbation theory accounts for band-structure effects. An extrapolation of this quasi-localized approach yields physically reasonable results, which makes it possible to interpolate between the delocalized band-structure and localized Heisenberg limits. Using Stoner-type magnetic energies derived from paramagnetic band-structure calculations it is argued that the comparatively low Curie temperature of iron-rich rare-earth intermetallics such as R₂Fe₁₇ originates from their quasi-weak ferromagnetism. Upon interstitial modification, these materials leave the quasi-weak limit and become nearly strong ferromagnets with enhanced Curie temperature.

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  Using the KKR Green's function band structure calculation, the electronic and magnetic structures in Fe_n/Co_m and Fe_n/Ni_m (n,m=1∼5, n=1 and m=9) multilayer systems are investigated. The lattice constants of Fe₃/Co₃ and Fe₃/Ni₃ multilayers are evaluated to be those of bulk bcc Fe and bulk bcc Co and Ni. An oscillation of the length of local spin moment from monolayer to monolayer is observed in the Ni layers, while it is hardly observed in the Co layers. Although the effects of interfaces on the local spin moment at the site in the interfacial monolayers are slightly larger in the [100] stacked system than in the [110] stacked one, the behaviors of the local spin moment distributions are the same between the two cases.

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  We have sputter deposited (Pt/Co/Pt)/X multilayers (MLs) with the thickness of the Pt layers corresponding to one atomic monolayer, i.e., 2.3 Å, and X=Pd,Ag,Cu,Ni. The Kerr rotation, Θ_K, perpendicular anisotropy energy, K_⊥, and magnetic coercivity, Hc, all improve dramatically in the sputter-deposited (Pt/Co/Pt)/X films over the corresponding Co/X multilayers. In the (Pt/Co/Pt)/Pd case the films show considerable property improvement over both Co/Pt and Co/Pd multilayers. When X=Ag,Cu,Ni the increase in K_⊥ is approximately ten-fold compared to Co/X MLs and the Kerr rotation is high (∼0.15°-0.3°) and comparable to that of Co/Pt films at short wavelengths.

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  We report in situ measurements of the stress and clarify the contribution of stress-induced anisotropy to the magnetic anisotropy in Co/Pd multilayer films prepared by dc magnetron sputtering. Stress of a multilayer film was measured in situ during the deposition using a home-made optical displacement probe. The sensitivity of the displacement probe was 5.9μ V/Å and it turned out to be good enough to detect stress caused by deposition of a monoatomic-layer-thick Co and Pd. The stress-induced anisotropy is ranged between 1.9 × 10⁶ erg/cm³ and 3.1 × 10⁶ erg/cm³ in our samples. In comparison with contribution of the Néel's surface anisotropy, this magnetoelastic contribution to the perpendicular magnetic anisotropy is estimated from 40% ∼ 50%.

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  Observations of domain structure in Co/Pd multilayers indicate that the shape and the size of the domains as well as their growth strongly depends on the substrate conditions and the total thickness of the film. Multilayers of Co/Pd were fabricated by sputtering in Ar at a pressure of 20 mTorr onto various substrate conditions and thickness. The Co and Pd layers were deposited by rf (radio frequency) and dc (direct current) magnetron sputtering, respectively. Four different conditions were chosen, namely the multilayers were deposited onto Si(111) substrate, Si(111) etched substrate, and unetched SiN film which was deposited onto Si(111) and etched SiN film on Si(111).

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  The uniaxial anisotropy K_u, the coercive energy E_c and the Bloch wall energy σ_w were measured as a function of Nd content and temperature. Nd showed no significant contribution to K_u on TbNd-FeCo films with Tb contents of more than 15 at% . The determined relation between E_c and K_u indicated that the magnetization reversal process was dominated by domain wall movement. σ_w has been determined for TbNd-FeCo magneto-optic disks. The procedure consists of applying a magnetic field to thermomagnetically written cylindrical domains and measuring the magnetic fields for which the domains expand and collapse. The wall energy can then be calculated from the difference of both fields. σ_w decreased continuously with increasing Nd content, reaching about one third of its initial value for more than 15 at% Nd. This effect cannot be explained by a corresponding decrease in the exchange stiffness constant A or the anisotropy constant K_u Therefore, we conclude that the simple formula for the Bloch wall energy is no longer valid due to the strong distortion induced by the Nd causing locally a sperimagnetic structure. which disturbs significantly the magnetic ground state.

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  A structural analysis of amorphous TbFeCo films has been performed by using EXAFS of as-deposited and annealed samples. It is found that the numbers of inplane Fe-Fe (and Fe-Co) pairs for as-deposited TbFeCo are larger than in the perpendicular direction. On the other hand, in the case of the annealed samples, the number of in-plane Fe-Fe pairs is smaller than in the perpendicular direction. Thus, the direction of the structural anisotropy of the TbFeCo film changes 90 degree due to the annealing procedure. However, the direction of the perpendicular magnetic anisotropy of the TbFeCo does not change before and after the annealing procedure.

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  For two amorphous DyGdFe films, one with weak coherent uniaxial anisotropy normal to the film plane (CA) and the other with strong CA, we measured magnetization and ac susceptibilities in small de fields (H). The results suggest that a ferrimagnetic-like phase is induced by the strong CA even for H=0.

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  Microstructure and the electronic property of amorphous (Tb_0.5Gd_0.5)_X Fe_100-X (X= 10∼30) films with a giant perpendicular magnetic anisotropy (GPMA, the uniaxial anisotropy constant K_u =∼10⁷ erg/em³) have been studied in detail. As a result it is found that these films consist of large “crystals” of which the local atomic arrangement is similar to GdFe₅ (CaCu₅-type, hexagonal) and their c-axes orient in the normal direction to the film plane. Therefore, the GPMA is considered to be generated from the “crystalline” phase. Considering the large electrical resistivity of these films, perpendicular anisotropy is probably induced by the random pair formation of neighboring rare earth (RE=Tb,Gd) atoms in the <001> direction of the REFe₅ structure.

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