Details are given of a method of measuring perpendicular magnetic alumite discs using anodization with an additional new process called “pore widening” which is effective in controlling the coercive force. Electro-deposited fine iron needles were in a single crystalline state, and the perpendicular orientation of magnetization was confirmed. The resulting magnetic recording characteristics of the rigid discs were satisfactory, indicating usefulness of the method as a perpendicular recording medium.

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Partially oxidized Fe-Co films were prepared by reactive RF magnetron sputtering. They have a large perpendicular magnetic anisotropy K_u (larger than 2 × 10⁶ erg/cc) and saturation magnetization M_s (larger than 700 emu/cc), which are comparable to those of CoCr films.
X-Ray diffraction analysis showed that the film consisted of metal and oxide. It is thought that the shape effect is important as the origin of large perpendicular anisotropy.
Writing and reading at 90 kFRPI for the medium that has a soft magnetic under-layer was also possible.

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We have studied dependence of Bi composition on the perpendicular magnetic anisotropy of evaporated thin films from Fe_100-xBi_x evaporant at the film growth site. The films were prepared by a one-point vacuum evaporation method in which Fe and Bi were put in the same place. The evaporated films clearly showed perpendicular magnetization characteristics at x = 1.6 at%. The saturation magnetization: 4πM_s, remanent magnetization: 4πM_r⊥, and coercive force: H_c⊥, were 20 × 10³ (G), 0.6 × 10³ (G), and 500 (Oe), respectively. One cause of the increase in the magnetization is thought to be the effect of a perpendicular configuration for Fecolumn grains growth which is constituted just as Bi reevaporates. Namely, formation of regular column grains with excellent orientations had a favorable influence upon the magnetization characteristics. We inquired into the process of the growth of the films by X-ray diffractometer, AES analysis, and SEM photographs and found the optimum production of the film.

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It has been reported that outgoing gas from a substrate affects the magnetic properties of Co-Cr film during deposition of Co-Cr on the substrate.
Therefore, the procedure of degassing a substrate by heating it in a vacuum prior to formation of Co-Cr film is necessary to reduce the amount of outgoing gas if high perpendicular magnetic anisotropy of the Co-Cr film is to be obtained for perpendicular magnetic recording media.
Three kinds of polymer substrate were used to study the influence of the degassing procedure on the properties of Co-Cr film deposited on each polymer substrate by changing sputtering Ar pressure. With polyimide film which has high water absorption and high glass transition temperature, the degassing at 100 °C in a vacuum is not sufficient to increase magnetic anisotropy of Co-Cr film. The large amount of outgoing gas from a substrate such as polyimide disturbs the crystal orientation of Co-Cr and reduces the magnetic anisotropy of Co-Cr film. But a comparatively small amount of outgoing gas from a substrate such as PET film prevents Cr atoms from segregating at the columnar boundary and reduces coercive force in the perpendicular direction.

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The effect of ion bombardment during film growth was investigated on perpendicular anisotropy CoCr films. Films were prepared by a web-coater type evaporating system equipped with a Kaufman 3 cm ion source. M_s, H_c⊥ and Δθ₅₀ decreased while H_k⊥ and grain size increased in bombarded films. These results indicate the reduction of crystallographic defects and Cr segregation, suggesting that the grain boundary plays an important role in the segregation.

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Co-Cr films were prepared on polyimide substrates with temperatures of T_s=27°C and T_s > 150°C by rf sputtering method with application of a magnetic field H_a up to 41 Oe normal to substrates and/or a negative bias voltage V_B up to 150 V at substrates. The films of T_s=27°C have good orientation of c-axis (Δθ₅₀=3.2°) and show magnetization values near those of the bulk materials. In these films, we were able to obtain reentrant perpendicular hysteresis loops having low coercivity H_{c (⊥)} and sharp shoulder, and could observe stripe domains with a width of about 0.3μm and also the clear wall motion by the Bitter method. The application of H_a induces a change in Cr-content, saturation magnetization M_s and perpendicular anisotropy K_u. The c-axis orientation is improved by applying V_B up to 50 V and the value of Δθ₅₀ becomes larger. In films of T_s=150°C, the values of M_s, K_u and H_{c (⊥)} are higher and c-axis orientation is worse than in films of T_s=27°C.

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A roll coater system was investigated for establishment of a mass production system for Co-Cr perpendicular recording media. Improvements of the crystal orientation and the magnetic properties of Co-Cr media with the introduction of new seed layers of Co-Cr itself are described. In the light of these results, a Co-Cr film with a composition gradient in the growing direction but without any seed layer has been proposed and its properties discussed. It was found that the anisotropy field H_k can be remarkably increased for the film with a composition gradient over that of a conventional Co-Cr film. It is concluded that the newly developed Co-Cr film is very suitable for mass production by a roll coater because of its simplified process which requires no sputtering of any seed layers.

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Double layer CoCr films with under-layer CoCr of various compositions were continuously prepared by DC magnetron sputtering equipment on PET film.
The dependences of H_c and H_k of double layer CoCr film on Cr concentration of under-layer CoCr film were measured. When the Cr concentration of the under-layer is higher than that of the over-layer, the H_k of double layer is larger than that of single layer film. In the case of lower Cr concentration of the under-layer than that of the over-layer, the result is the opposite. On the other hand, the dependence of H_c on Cr concentration of the under-layer film is contrary to that of H_k.
According to TEM observation, double layer film with an under-layer of high Cr concentration has larger grain size than does single layer film.

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The domain structures of cores with patterned permalloy films are investigated in order to develop magnetic recording thin film heads with narrow track widths. For single layered permalloy films, domain patterns indicate that the writing and reading abilities decrease when the track width becomes less than 10μm. For six layered permalloy films with an alumina interlayer of 0.02μm thickness, domain patterns show that domain walls remain oriented along the direction of the track width even at the width of 7μm. Furthermore, six layered permalloy films with small anisotropy field show no change of wall positions when the external magnetic field is applied along the hard axis. It is thus concluded that six layered permalloy films with small anisotropy field are most suitable for magnetic recording thin film heads with narrow track widths.

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The shapes of magnetoresistive (MR) elements which suppress Barkhausen noise originating from domain activity were studied. We particularly attempted to suppress the Barkhausen noise by using a flux closure scheme which consists of shaping the MR element into a “picture-frame” geometry with a small gap (called a Closed Type MR element).
We investigated MR response of the CTMR element and compared it with the conventional MR element shaped stripe. In the stripe element, when the length was shorter than 100μm, Barkhausen noise was observed throughout the region of the sensor by a Kerr-effect microscope. On the contrary, the CTMR element exhibited quiet response in most of the sensor region. We found that an MR head with track pitch of less than 40μm could be realized, based on the design of the optimum sensor region.
We fabricated Yoke Type MR heads which incorporated the CTMR element or the stripe element in the magnetic yoke, and evaluated the difference in the reproducing characteristics between these elements. The results showed that the noise level was 10dB lower for the CTMR element than for the stripe element and higher harmonics distortion decreased.

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Performance improvement for a magnetic read-out head using induced RF permeability change has been attempted from both electric and magnetic standpoints.
First of all, from an electric viewpoint, the practical system noise reduction method capability for this new head was investigated. Results show that the system noise can be reduced accompanying an increase in reproducing sensitivity, by supplying an optimum forward bias voltage to a diode composing the peak-detector. Consequently, it has been confirmed that this method leads to a 6-10 dB improvement in the carrier-to-noise ratio for a read-out signal.
From a magnetic standpoint, output voltage response to magnetic fields was investigated with magnetic film thickness as a parameter. Reproducing sensitivity was found to be suppressed by the eddy current and the demagnetizing field for an exciting RF magnetic field (Hrf), with increasing film thickness, if the domain behavior effect can be neglected. It is expected that the closed magnetic circuit for Hrf, as well as a signal field, will diminish this suppression.

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MIG head which has metal magnetic thin film in the gap, has been developed for high coercivity medium. But the head has problems of the pseudo output caused by the pseudo gap at the boundary plane between Fe-Al-Si alloy thin film and ferrite, and low R/W efficiency. The pseudo gap is caused by a damaged layer in the ferrite and the first layer of Fe-Al-Si film that is about 0.1 μm thick and about 10 in permeability. The result that the first layer is examined in the magnetic characteristics presents that it causes the pseudo output. These problems are solved by inserting Ni-Fe intermediate thin film between Fe-Al-Si film and ferrite, which lowers coercive force of Fe-Al-Si thin film and significantly reduces the pseudo output.

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The feasibility of high bit density recording was investigated experimentally in a perpendicular magnetic recording system using a single pole head and a Co-Cr/Ni-Fe double layer medium. To improve the reproducing sensitivity and resolution, the following were adopted: (a) Use of a newly developed high-sensitive single pole head. (b) Use of a medium with a relatively thin (0.1 μm) Co-Cr layer and a thick (0.5μm) Ni-Fe underlayer. (c) Achievement of head-to-medium spacings less than 0.03μm. As a result, reproduced signals were detected up to 680 kFRPI. The recording bit length at the highest density was of the order of the Co-Cr column diameter of the medium. This result proves that the high density recording up to the intrinsic limit of the medium is possible because this method is free from recording demagnetization effects at high densities.

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A new recording layer construction of a double layer perpendicular recording media is proposed. The recording layer is constituted of double layers, a high H_{c (⊥)} layer of the surface side and a low H_{c (⊥)} layer of the soft magnetic layer side. The recording sensitivity is improved without decreasing the reproduced voltage. Total thickness of the recording layer is set at 0.3 μm, and coercivities of the high and low H_{c (⊥)} layers are set at 650 Oe and 350 Oe, respectively.
The satisfactory result is explained by the reproduced voltage depending strongly on the coercivity of the recording layer of the surface side, but not of the soft magnetic layer side; the recording sensitivity then mostly depends on the average coercivity of the recording layer. This new recording layer construction is useful to secure degradation of the recording and over-write sensitivities accompanied by thinning of the main pole thickness of the recording head. The Double-Recording-Layer media reported here is also useful to improve the reproduced voltage of media, since the recording sensitivity is raised without decreasing the total thickness of the recording layer.

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In order to compute the vectorial magnetization process of a crystalline particle in a Co-Cr sputtered film, a magnetization reversal model was investigated. A curling mode and a statistical method were introduced for the calculation of a probable vectorial magnetization of the particle. Using this method, the M-H loops of Co-Cr films were restored well by computer. Simulation of the perpendicular magnetic recording process was carried out in good agreement with the measured reproduced waveforms.

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A novel head system composed of four ball-shaped pads and one small-sized head of a single pole type was investigated for driving of a Co-Cr/permalloy flexible disk of 3.5″ diameter. In the disk drive, the head system was scanned from a position with a radius of from 32 to 38 mm at rates ranging from 400 to 1000 rpm to evaluate the influence on read-write characteristics and the penetration of the SPT head. Steady read-write characteristics were observed in the high density region of some 70 kfci.
Since this system is structured to relax the excess stress on the head and the disk, improvement in signal durability is expected in addition to the steady read-write characteristics.

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Durability of CoCr thin film media on head running condition is important in practical application. During head running, some phenomena such as scratch, crack and removal of the CoCr thin film from PET are locally on the surface of the media. One of the methods of obstructing these phenomena is to form a protective layer on the CoCr thin film. In this report, fluoride oil, fluoride resin and CoCrO_x thin film are studied by the observation of a scratch and the measurement of friction coefficient. The scratch is made by a diamond or steel needle with 50μm or 500μm radius under contact loads from 1 grf to 80 grf. It is shown that CoCrO_x thin film is not as easily scratched as other organic films; its friction coefficient is small on media with small surface roughness and shows a constant value which does not depend on load applied to the needle.

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Magnetization distributions around vertical Bloch lines (VBL's) in the wall-center plane are calculated by direct minimization of the energy of the system. A successive approximation method using the Newton's method has been developed to solve the Euler equation numerically. The method has been found very effective to obtain equilibrium configurations in small iteration steps as compared with the dynamic calculation based on the so-called equation of wall motion. The calculation includes two-dimensional VBL's in which variations along the Z-axis are neglected and three-dimensional VBL's in which surface-to-surface magnetization twist is taken into consideration. Effective interaction field between two VBL's is calculated as a function of the VBL separation in both cases. The paper descibes the formulation of the problem, method of numerical calculation, and results.

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Relationship between surface mode perpendicular ferromagnetic resonance (spin wave resonance) spectrum patterns and anisotropy field profiles has been studied for ion-implanted garnet films. Implantation depth markedly changes the mode of the spectrum. Profile of anisotropy field H_k mainly changes the line position at high external field region. On the contrary, H_k profile at boundary region between implated and un-implanted layer changes the line position at low field (near the main body mode). Existence of an extremely large H_k, region in the profile produces ‘trapped modes’ which appear separately at high field. Examples of spin wave resonance spectrum for H₂⁺ implanted Bi-substituted garnet films for 1 μm bubble devices are also shown. It is possible to monitor the ion-implantation process by measuring the spectrum.

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The write gate for Bloch line memory devices have been investigated by computer simulations and experiments. In the case of conventional gates where a write conductor is located at the stripe domain head, the computer simulation shows that the VBL-pair generation takes place in such a way that the horizontal wall magnetization between the generated VBL's is opposite in direction to the applied in-plane field H_ip. As a result, the VBL's collapse easily when the write current is small. To overcome this shortcoming, a new write gate where the write conductor is located along the stripe domain wall has been designed and examined. In this gate. VBL's are stable because the generated VBL's have the horizontal magnetization in the same direction as H_ip. While the current margin of a conventional gate is about 6%, the new gate has been confirmed experimentally to show a greatly improved current margin as high as 77% at H_ip of 7 Oe.

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Highly Bi-substituted films of YIG were prepared on <111> oriented (GdCa)₃(GaMgZr)₅O₁₂ substrates by using a reactive ion beam sputtering (IBS) method. In films deposited without substrate heating, <111> oriented garnet crystal phase together with secondary phases were formed by post-deposition annealing. Epitaxial growth of single-phase garnet films was achieved in situ when depositing at ∼550°C In the post-deposition annealed films and the epitaxially grown films, the maximum Bi-contents were 1.93 and 2.16 atoms/f.u., respectively, and the Faraday rotation at a wavelength of 633 nm resulted in -4.3 × 10⁴ and -5.25 × 10⁴ deg/cm, respectively. The Bi-content of 2.16 atoms/f.u. is much higher than that of 1.97 atoms/f.u. expected as the theoretical limit for bulk YIG, which suggests that such a heavy Bi-substitution is achieved through non-thermal equilibrium process characteristic of IBS. It was also revealed that Bi-content in films strongly depended on O₂ partial pressure.

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Annealing effects in H₂-atmosphere on the optical absorption loss and lattice constant are studied for Ca- and Si-doped YIG and Ca-doped (BiGd)₃(FeAlGa)₅O₁₂ films grown by LPE technique. H₂-annealing was done at 150∼500°C for 22 hrs. The absorption loss and lattice constant in YIG films with poor impurities or doped Si did not change by H₂-annealing at 150 ∼450°C, however, those in Ca-doped YIG and Bi-substituted garnet films changed notably. The changes of the absorption loss are explained by the reduction of Fe ions. The minimum value of the absorption loss was about 250 dB/cm at λ = 0.8μm for both Ca-doped and Ca-free garnet films. These results show that H₂-annealing is effective to get iron garnet films with a high figure of merit. The lattice constant increased with increase of annealing temperature, and only in Ca-doped YIG films it decreased drastically at 450°C.

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Temperature dependence of Faraday rotation, which causes degradation of isolation at high or low temperature for an optical isolator, was measured at 1.3 and 0.78 μm wave lengths together with saturation magnetization and optical transparency for epitaxially grown (TbBi)₃Fe₅O₁₂ films. Temperature dependence of Faraday rotation for these films was smaller than that for (GdBi)₃(FeAlGa)₅O₁₂ films and (GdBi)₃Fe₅O₁₂ bulk single crystals. Particularly, Tb_2.13Bi_0.87Fe₅O₁₂ films showed only a 2.1% shift in Faraday rotation from that measured at 25°C in the temperature range 0∼50°C. These values correspond to those of Y₃Fe₅O₁₂ bulk single crystals. Additionally, (TbBi)₃Fe₅O₁₂ films had a smaller saturation magnetization than Y₃Fe₅O₁₂ and sufficient optical transparency in 1.3∼1.5 μm wavelength for an optical isolator.

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We have studied two methods for improvement of Faraday rotation temperature dependence in (BiRe)IG for optical isolators, where Re denotes rare-earth ion. One method is utilization of Tb for Re in (Bi_xRe_3-x)Fe₅O₁₂. We measured Tb concentration dependence of Faraday rotation (θ_F) and its temperature dependent deviation coefficient from 45 degrees (≡ β). β decreased with increasing Tb concentration (3-x) and became zero between (3-x) =2.4 and 2.5 at which Faraday rotation was θ_F = −400∼ −600 deg/cm of λ = 1.3μm . In this case. new substrates with lattice constants of 12.47Å and thick films of 0.7∼1.1 mm are required. The other method is the two-step-epitaxial method, where (BiLuGd)IG is employed with any of (TbLa)IG, Tb(FeSc)G and Tb(FeIn)G. We achieved β=0.04deg/°C in (BiLuGd)IG/Tb(FeSc)G and β=0.00 deg/°C in (BiLuGd)IG/(TbLa)IG. θ_F values for these Tb garnets were smaller than calculated values using Crossley's model. Pb contamination in Tb garnets and canting of Tb sublattice magnetization are plausible reasons for this effect.

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Highly Bi-substituted LPE garnet films, Bi_0.85Lu_2.15Fe₅O₁₂ and Bi_1.4Y_1.6Fe₅O₁₂ have been grown with FMR linewidth as small as YIG, using only Bi₂O₃ as a flux. Substitution of Al for Fe increases ΔH rapidly. The minimum value of ΔH obtained was 1.5 Oe for Bi_0.85Lu_2.15Fe₅O₁₂ films and 0.73 Oe for Bi_1.4Y_1.6Fe₅O₁₂ films, which is the smallest value reported to date for such highly Bi-substituted garnet films. This could be ascribed to there being no Pb incorporation into the film.
It was experimentally observed that MSSW propagation was possible for Bi_0.85Lu_2.15Fe₅O₁₂ films.
These films are very promising for MSW-based optical waveguided devices since they have ten times larger specific Faraday rotation than YIG as well as a very small optical adsorption coefficient at 1.3μm wavelength.

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Effect of the low symmetry crystal field S₄ was investigated on the spectral shape of Faraday rotation in ferrites containing tetrahedral Co²⁺ ions.
The calculated shape of Faraday rotation in ⁴T₁(⁴F) becomes broad with increasing α′, a parameter proportional to the magnitude of the low symmetry field (S₄), above about 1000 cm ^-1 , and has a shoulder or other structure when α′ ≥ 2000 cm ^-1.
Using α′ = 2000 cm ^-1 explains well the broad shape of the experimentally observed Faraday rotation at about 1.5 μm in a (Y_2.8Gd_0.2)(Fe_4.6Co_0.2Ge_0.2)O₁₂ thin film grown by the conventional liquid phase epitaxy (LPE) method.

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Magneto-optical properties of rf-sputtered PtMnSb/TbFe films with a double layered structure have been investigated to improve the magnetic and magneto-optical properties of a PtMnSb monolayered film.
Measurements of polar Kerr effect of PtMnSb/TbFe double layered films were made using a Xe lamp under an external magnetic field H=5 kOe. The Kerr rotation peak of the films was found to shift at a wavelength shorter than that of PtMnSb monolayered film. The coercive force H_c of the PtMnSb/TbFe double layered films was found to be about 700 Oe, which was six times as large as that of PtMnSb monolavered film.

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Magnetic and magneto-optical properties of TbFeB films prepared by rf-sputtering have been investigated. Amorphous films of Tb₂Fe₁₄B with perpendicular magnetization were obtained when rf-power 50 W was applied. The amorphous films were found to have a value of polar Kerr rotation θ_K ≅ 0.2 deg at He-Ne laser wavelength (632.8 nm). Coercive force (H_c) measured using a vibrating sample magnetometer (VSM) and resistivity (ρ) varied with the concentration of B in TbFeB films, and each had a peak value at the B concentration x=0.05. Curie temperature (T_c) and compensation teperature (T_Comp) were found to be 90∼100°C and 70°C, respectively, from measurements of the temperature dependence of θ_K.

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Co based amorphous binary alloy films. Co_100-xR_x (10≤x≤55, R=Pr, Nd) were prepared on glass substrates using the electron beam evaporation technique. From magnetic and magneto-optical viewpoints, systematic experimental investigations were carried out on these films. As a result, (i) the dependence of perpendicular magnetic anisotropy constant with the correction of 2πM_s², K_⊥, on temperature and composition, and (ii) the dependence of polar Kerr rotatiom angle, θ_K, on wavelength, λ (0.4∼1.1μm) and composition were systematically clarified. A maximum value of K_⊥ of about 6 × 10⁶ erg/cm³ at 77 K was obtained for Co-Nd amorphous film with 25 at% Nd concentration. K_⊥ decreases monotonically with increasing temperature and becomes zero around 400 K. This temperature at which K_⊥ disappeared was nearly the same for all the films examined regardless of alloy composition. A maximum value of θ_K, 0.38 deg (λ=0.4μm) in the present amorphous films was obtained at about 11 at% Nd concentration. The peak at which the minimum value of θ_K is observed shifts from 0.46μm (Co) to 0.65μm (31 at% Pr, Nd) in wavelength with increasing Pr, Nd concentration. Change of the magneto-optical active transition induced by the existence of Pr and Nd atom was found to be remarkable around at 30 at% rare earth concentration.

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Highly pure single crystals of YIG are obtained by an FZ method and a remarkable photoinduced change of permeability is observed. Permeability is decreased over 90% by illumination of white light at 77 K and the influence remains up to about 260 K. By an annealing at 1100°C (oxygen atmosphere, 6 hours) in the sample preparation stage, the magnitude of the effect is reduced to 40%. After the sample is illuminated strongly at 77 K, the loss factor below 5 kHz shows double peaks, contrasting with the unilluminated flat curve on warming to 300 K. These activation energies are obtained as 0.3 and 0.1 eV. The mechanism of the effect is discussed in relation to relaxation processes with which these peaks are concerned, and F° center, an oxygen vacancy with two trapped electrons, is supposed to play an essential part.

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To investigate properties of Bi-substituted garnet film with many oxygen deficiencies, Bi, Ga : DyIG films have been prepared by sputtering in Ar+H₂ gas (H₂: 0∼5% in partial pressure) and post-deposition annealing for crystallization. When H₂ concentration in sputter gas increased, the Bi content of the film decreased. The film sputtered in Ar+H₂ crystallized as a garnet single phase at relatively low temperature (560°C for Bi=1.5) even when it had low Bi content and non-stoichiometry. The optical homogeneity of the film remarkably improved with increasing H₂ concentration; optical scattering due to crystal grain boundaries was reduced further than that of the film sputtered in pure Ar. This is associated with many defects remaining in the crystal grains even after annealing, as confirmed by the extent of the linewidth of X-ray diffraction. The magnetization and Faraday rotation hysteresis of the films sputtered in Ar+H₂ showed anomalous curves, which may have been caused by an impurity phase undetectable by X-ray diffraction measurement.

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Magnetic and magneto-optical properties of (Nd, Pr)-(Fe, Co) amorphous films fabricated onto heated substrates by r.f. sputtering are discussed in conjunction with structure. The perpendicular magnetic anisotropy is strongly dependent on temperature, concentration and film thickness. These results together with structural information suggest that the origin of the perpendicular magnetic anisotropy is closely related to atomic short range ordering of fine crystalline clusters inherited through the film growth.
The polar Kerr rotation angle increases with decreasing wavelength for the alloys of light rare earths, in contrast to those with heavy rare earth elements.

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Magneto-optical properties and corrosion resistance of amorphous Tb-Fe-Co films containing noble metals (Pt, Au, Ag and Cu) have been investigated from the viewpoint of application. By addition of these noble metals, the Curie temperature T_c is increased. The Kerr rotation angle θ_Ks is also increased by addition of Pt and Cu. However, the direct correlation between the Kerr rotation angle and the Curie temperature T_c is not observed. The figure of merit √R · θ_Ks is improved by addition of these noble metals, especially Pt and Cu. The corrosion resistance is improved by addition of these noble metals to Tb-Fe-Co amorphous films.

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Magneto-optic Kerr effect of amorphous (a-)GdFe films has been investigated by separating each magneto-optic contribution of Gd and Fe. Amorphous GdCu and YFe alloy films which consist of a single magnetic element have been prepared and their magnetization and polar Kerr rotation in the wavelength range of 400-700 nm have been measured at liq. N₂ temperature. From the Kerr spectra of a-GdCu and a-YFe and their magnetization, the constant K(λ) defined by θ_K=K(λ), M(T) has been estimated. Using the K(λ) values we have separated each contribution of Gd and Fe to the Kerr rotation of a-GdFe. Comparing the Kerr spectrum of a-GdFe with that calculated from θ_K= K_Gd(λ) · M_Gd(T)+K_Fe(λ) · M_Fe(T), the Kerr spectrum of a-GdFe is fairly well explained by superposition of the contribution of Gd and Fe. It is concluded that the contribution of each sublattice is quite dependent on the photon energy in the range of 1.5 to 3 eV. Especially, the contribution of Gd becomes large with increasing photon energy and comparable to that of Fe at λ =400 nm.

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Magneto-optic and magnetic properties on compositionally modulated TbCo films were studied. Films were prepared on glass substrates using RF sputtering method by modulating substrate bias voltage with a sequence of -200 V/0 V/....../0 V or -250 V/0 V/....../0 V. Single layered films of 0 V have high perpendicular magnetic anisotropy (K_u), small Kerr rotation angle (θ_K) and good chemical stability, while high biased films have low K_u large θ_K and poor chemical stability. The period of modulation was changed to between 1500Å and 40 Å and was confirmed by Rutherford backscattering spectrometry and X-ray small angle scattering method. The modulated films showed higher K_u and resistivity to oxidation. High θ_K and high reflectivity can be obtained at glass side by this multi-layered structure.

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Rare earth-transition metal amorphous films are promising for use in erasable optical memory media. A number of studies have been made of corrosion or reliability of the media, and for practical use, more systematic tests on corrosion and reliability are essential. We have studied dependences of pitting corrosion on aging humidity and temperature. Specimens were noncoated, SiO-coated, or SiO₂-coated TbFe and TbCoFeTi films deposited onto glass substrates by RF sputtering and were aged at a variety of humidity and temperature conditions. The degree of corrosion was quantified by transmittance changes of the specimens. Relative humidity was an accelerating factor of the corrosion for all the specimens, but temperature was only for the coated specimens. High temperature and humidity tests are good accelerative tests of the corrosion for the coated specimens but not for the noncoated specimens.

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The lifetime estimate of a magneto-optical disk which has GdTbFe for the magnetic layer, AlN for dielectric layers, and AI for the reflective layer was discussed. In order to study the aging characteristics, accelerated aging tests were performed by changing the ambient temperature (20∼100°C in air). In addition to the coercivity, recording sensitivity which was evaluated with recorded bit length was chosen as the basis on which the lifetime was estimated quantitatively.
As the aging time grew longer, the recording sensitivity tended to decrease. The higher the aging temperature, the larger the decrease rate was. Using the Arrhenius method, the magneto-optical disk with the quadri-layer structure mentioned has an expectant lifetime of about 18 years, which is long enough for optical data storage application.

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An important subject remains in realizing an optical data system using a magneto-optical disc. It is a function of real-time recording and erasure of information. We developed an optical head using a laser diode array with three elements and realized its function. We also measured real-time recording/erasure characteristics against composition of a TbFeCo disc by using the optical head and six TbFeCo discs of different composition. The characteristics were estimated by measuring carrier-to-noise ratio and block error rate in Compact Disc formats. Real-time recording/erasure could be performed by applied magnetic field of more than 400 Oe. But a TbFeCo disc of composition in the neighborhood of magnetic compensation point had better characteristics against deviation of applied magnetic field and record power than one of other composition. In result a TbFeCo disc of 23∼27 at%Tb is better for real-time recording/erasure with an optical head using a laser diode array.

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Measurements of magnetization and susceptibility were carried out in the temperature range from 4.2 to 300 K for amorphous Co_100-xR_x (R=Pr, Nd, Sm; 50 ≤ x ≤ 70) alloys prepared by a rapid quenching technique. The magnetic behaviour of the Co-R amorphous alloys was discussed based on a local moment model. It is suggested that the Co ion loses its moment around x=60 assuming the rare earth ions retain their normal R³⁺ character and that the magnetic contributions of R in these disordered systems are similar.

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Structure and hard magnetic properties for the rapidly quenched SmCo_5-xB_x (O ≤ x ≤ 1) and Sm(Co_1-xFe_x)₄B(O ≤ x ≤ 0.74) alloy ribbons, which were fabricated under the various quenching rate, were systematically examined. Metastable states, such as CaCa₅ type disordered structure whose superstructure is CeCo₄B type and amorphous state were obtained in the wide composition range, O.6 ≤ x ≤ 1 for SmCo_5-xB_x and O ≤ x ≤ 0.5 for Sm(Co_1-xFe_x)₄B in the ribbons fabricated under high quenching rate. The maximum value of _iH_c (> 18 kOe) was obtained for the ribbons which consist of CaCu₅ disordered structure as a single phase. Furthermore, in the case of CaCu₅ disordered structure, the value of T_C remarkably increased with increasing Fe and decreasing B content (SmCo₄B(T_C= 197°C)→SmCo_0.4B_0.6(T_C=557°C), Sm(Co_0.5Fe_0.5)₄B(T_C=472°C)). The value of M (H_ex=18 kOe) also increased with increasing Fe and decreasing B content. It was concluded that the formation of CaCu₅ type disordered Sm (Co-Fe-B)₅ compound with high Fe and low B content was considered to be effective to improve the hard magnetic properties for Sm-Co based alloys.

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In melt-spun ribbons of Didymium (Nd-10 %Pr)-Fe-B and Ce-didymium (Nd-15 %Pr-5 %Ce)-Fe-B alloys prepared by the single roller method, the effects of composition, substrate surface velocity and subsequent annealing on the magnetic properties were studied, and their bonded magnets were made of the optimum-quenched ribbons. A maximum energy product of 93.6 kJ/m³ was obtained with 34 wt% (Ce-didymium)-65 wt%Fe-1 wt%B ribbon prepared at a substrate surface velocity of 11.8 m/s.
The best magnetic properties obtained in these bonded magnets of 34 wt% (Ce-didymium) -65 wt%Fe-1 wt%B alloy were B_r=0.595 T, H_CJ= 1410 kA/m, H_CB =400 kA/m and (BH)_max=60.3 _KJ/m³. The temperature coefficients (from 25 to 125°C) of B_r and H_CB for these bonded magnets were −0.154%/°C and −0.180%/°C, respectively.

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Effects of rare-earth oxides addition on the magnetic properties of the Nd-Fe-B sintered magnets are studied. The addition of Dy₂O₃ and Tb₄O₇ increases the intrinsic coercivity. For Dy₂O₃ addition, the optimum conditions for the powder mixing and Dy₂O₃ particle size are determined. A mixing time of over 10 minutes and the Dy₂O₃ particle size under 3μm are required to obtain a high intrinsic coercivity. EPMA measurements on NdFeBAl magnets added with Dy₂O₃ reveal an inhomogeneous distribution of Dy in the Nd₂Fe₁₄B matrix; Dy is rich near the grain boundary but poor inside of the matrix. Formation of such an inhomogeneous distribution of Dy atoms is attributed to reduction of Dy₂O₃ in the Nd-rich phases followed by diffusion of the Dy atoms into the matrix.

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Ribbons with compositions of Sm(Co_0.70-xFe_0.20Cu_0.10Zr_x)_7.5 (x=0-0.06) are prepared by meltspinning technique to examine the structures and magnetic properties of 2-17 type Sm-Co magnets. In the as-prepared state, these consist of predominantly single phase of disordered 1-7 phase. With the optimal aging treatment, the coercivity increases markedly with an increase in Zr content to reach the maximum value of 14.5 kOe at x=0.04. During the aging, the 1-7 phase transforms into a cellular structure of 2-17 and 1-5 phases, to exhibit high coercivity by pinning mechanism of the domain wall. With higher Zr contents, in particular. platelets of new precipitate phase are found to overlap the cellular structure. This is identified as a 1-3 phase of (Sm, Zr) (Co, Fe, Cu)₃, and presumably contributes to the coercivity enhancement.

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The effects of the partial substitution of Sm by Nd and a small addition of Ce to Sm₂(TM)₁₇ resin bonded magnets were studied. The obtained results were as follows:
1) Saturation magnetization, optimum solution temperature and anisotropy constant K₁ change linearly with Nd content. This result suggests that, depending upon the extent of substitution, Nd containing alloy has the same magnetic hardening mechanism and the same configuration of atoms except for rare earth atom as no substitution alloy.
2) Intrinsic coercive force decreases monotonously with Nd content. It is supposed that the cause of this is the decrease of domain wall energy difference between 1 : 5 phase and 2 : 17 phase.
3) Magnetic properties such as (BH)_max=14.5 MGOe, Br=8.1 kG, iH_c=11.2 kOe were achieved in Sm_0.5Nd_0.4Ce_0.1(Co_.672Cu_.08Fe_.22Zr_.28)_8.35 resin bonded magnet. Those values are comparable to no-substitution material data.

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Theoretical problems of amorphous ferrimagnets are discussed. Transition temperatures, compensation temperatures and thermal dependences of magnetizations in amorphous ferrimagnetic rare earth-transition metal alloys are investigated using the effective-field theory with correlations. Research on amorphous ferrimagnetic insulators is described. The obtained results suggest the opening of a new field of magnetism.

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The magnetostriction constants, λ₁₀₀ and λ₁₁₁, of Sendust alloys (7∼11 wt%Si, 4∼7 wt%Al, bal. Fe) were determined as a function of temperature between -196°C and 120°C by means of the strain gauge method. For the central composition of Sendust alloy (9.6 wt%Si, 5.7 wt%Al, bal. Fe), the sign of λ₁₀₀ is positive at -196°C and the magnitude of λ₁₀₀ is fairly large (≅1.3 × 10^-5). With increasing temperature, the magnitude of λ₁₀₀ gradually becomes small and crosses zero at room temperature. With continued increasing temperature, λ₁₀₀ again increases (-2 × 10^-6 at 120°C). In λ₁₁₁, however, no sign change took place for most of the alloys examined in this temperature range and the magnitude of λ₁₁₁ is nearly constant (e.g.,-1 × 10^-6 for the central composition of Sendust alloy). The composition at which λ_s=(2/5) λ₁₀₀+(3/5)/λ₁₁₁ becomes zero is strongly temperature dependent. With increasing temperature, the compositional line of λ_s=0 moves to the area with rich Fe and less Si concentration in the Fe-Si-AI ternary alloy system. The compositions at which λ_s=0 and K₁=0 are both realized exist on the composition line of about 84 wt%Fe. These composition shift to lower Si concentration along this composition line with increasing temperature.

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Temperature dependence of the magnetocrystalline anisotropy constant, K₁, and the magnetostriction constants, λ₁₀₀ and λ₁₁₁, was determined for the Fe₃(Al_1-xSi_x) alloy single crystals with D0₃ and B2 types of ordered structure. For the Fe₃(Al_1-xSi_x) alloys with D0₃ type of ordered structure, the value of K₁ at R.T. is -4 × 10⁴ erg/cm³ at x=0. With increasing x, K₁, decreases gradually and crosses zero around x ≅ 0.6. In alloys with B2 type of ordered structure, the value of K₁ is +2.9 × 10⁴erg/cm³ at x=0. With the slight increase of x, K₁ changes drastically in its sign and magnitude, and as a result, K₁=0 is realized at R.T. around 0.05 < x < 0.1. Temperature dependences of K₁ in this alloys with B2 structure are completely different from those of the alloys with D0₃ structure. The concentration dependence of λ₁₀₀ and λ₁₁₁ at room temperature for the alloys with B2 structure is similar to that for the alloys with D0₃ structure. The values of λ₁₀₀ and λ₁₁₁ at room temperature for the alloys with B2 structure are 70∼90% of that for the alloys with D0₃ structure.

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Reinforced Large Barkhausen effect and the Matteucci effect are realized applying a tension anneal to cold drawn amorphous magnetostrictive wires (Fe_77.5Si_7.5B₁₅ made by Unitika Co.). Sharpness and the amplitude of induced voltage pulses at the pick-up coil of the amorphous wire are proportional to the value of H*-H₀, where H* is the critical field of domain nucleation at the flux reversal, and H₀ is the critical field of domain-wall displacement. The value of H*-H₀ increased about ten times that of as-prepared wires. The Matteucci voltage was also increased in the tension annealed cold drawn wires. The critical length of the wire which shows the large Barkhausen effect could be reduced to about 20 mm (60mm for as-prepared wires). Therefore, small-sized rotation sensors are realized using the new wires.

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We have plated polycrystalline Co_xFe_3-xO₄ films by “thin liquid-film” method at T=55-90°C and pH=7.0 using NaNO₂ as an oxidizing agent. The film quality was improved by (1) introducing CH₃COONH₄ buffer which stabilizes the pH, and (2) filtering the reaction solution. Thus we obtained a film deposition rate of 300 Å/min at 90°C for x=0 and 0.43 without deterioration of the film quality. The deposition rate increased with the temperature. The films of Fe₃O₄ and Co_xFe_3-xO₄ (x=0.43) plated at 90°C on glass substrates exhibited a preferential texture of (100) and (111) planes respectively, parallel to the surface. Both films had a columnar structure normal to the surface plane, but the magnetization lay in the surface plane. Fe₃O₄ films plated at 90°C on α-Al₂O₃ (0001) and MgAl₂O₄ (100) crystal plates exhibited a preferential texture of (111) and (100) planes, respectively, the oxygen-packing layer of the substrate coinciding with that of the ferrite film.

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We have previously reported that the Fe-B-O system films fabricated by rf-reactive sputtering from composite targets of thin iron sheet, on which B₂O₃-tablets are placed, show pronounced properties of ferromagnetism and ferroelectricity simultaneously at room temperature. This method, however, lacks reproducibility of ferroelectricity due to poor controllability of water content in the films, which is considered to be essential for the ferroelectricity. To improve this situation, film fabrication was altered using targets of mixed powders of α-Fe₂O₃ and B₂O₃ and sputtering in mixed gases of argon, oxygen and hyrogen, where hydrogen was added to synthesize water. All films prepared showed dielectric hysteresis loop at room temperature. Magnetic, dielectric and optical properties of the films are presented in comparison with those by the previous method.

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