Durability of a Co-Cr perpendicular magnetic recording medium is studied with regard to its macroand microscopic surface profiles. Macroscopic deformation of medium caused by head sliding is investigated with a newly developed measurement system which uses laser light. Also, microscopic topography of the medium is estimated by spectral analysis of surface profile data. These are used for observation in head sliding. The medium starts to wear at the sites of protuberances, and the worn portions scratch the medium surface severely. It has been found that the period of durability before deformation of medium is entirely dependent on the initial profile. When the microscopic surface roughness of medium is so uniform that extraordinary protuberances cannot be observed, the macroscopic medium profile never changes during a period of examination of 72000 passes, suggesting a more durable medium.

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Dependence of perpendicular anisotropy of continuously vacuum deposited Co-Cr films on glow discharge treatment of polymer film surface and on thickness of Ti underlayers was investigated. The relation between the microstructure and the recording characteristics of the Co-Cr films was also studied. When the polymer film surface was pretreated by glow discharge with Ar gas, H_keff of the Co-Cr films decreased. On the other hand, using H₂ gas instead of Ar gas, deterioration of H_keff was negligible. The Co-Cr films deposited on the Ti underlayers had high H_keff independent of the condition of the glow discharge treatment. Thickness of the Ti underlayers had to be more than 40Å in order for the Co-Cr films to have small Δθ₅₀ such as 5-6°. Columnar structure of the Co-Cr films appeared when thickness of the Ti underlayers was in the range of 100-2000Å. The Co-Cr films consisting of columnar structure yielded high reproduced voltage.

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Magnetic properties of partially oxidized Fe-Co sputtered films are comparable to those of CoCr films. We studied the relationships between magnetic properties and recording characteristics using a combination of ring-type head and single layer medium. Recording density D₅₀ increased in proportion to anisotropy field H_k, and reproduced voltage depended on saturation magnetization 4πM_s and Co content. Maximum reproduced voltage was obtained in the 4πM_s region of 8500 to 11000 gauss at 60 at.% Co content. From X-ray diffraction analysis of these films, it is thought that reproduced voltage relates to microscopic structure of the films.

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This paper reports the relation between composition and characteristics of Co-Cr films prepared by DC magnetron sputtering. The composition of Co-Cr films can be controlled by changing the magnetic flux from magnet and solenoid coils. In films of high Cr content, a good orientation of c-axis and small in-plane squareness are obtained, while perpendicular coercivity and saturation magnetization are small. In-plane M-H loop of a Co-30 at.%Cr film shows that the film has large perpendicular anisotropy from the initial layer.

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It is well known that the magnetic properties of Co-Cr film vary with several sputtering parameters, among which impurities of sputtering gas and target are very important. However, the effect of impurities in the target has not previously been investigated. In this paper, we describe the effect of oxygen content in sputtering targets on the magnetic properties of Co-Cr film. In a range of a small amount of oxygen, with increasing oxygen content H_k and H_c(⊥) of Corich magnetic particles was thought to be enhanced. However, with further increase of oxygen content, the crystal orientation was so markedly degraded that the H_k and H_c(⊥) showed too small values for a perpendicular medium. This effect is more severe for thinner Co-Cr film below 0.1μm. Finally, it is concluded that the impurity oxygen content of the target should be as small as possible to realize excellent properties of the Co-Cr medium in a mass production system.

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Electroless plated Co alloy films for perpendicular magnetic recording media were investigated as a means of controlling magnetic properties by changing the catalyzing process. In the thin region, such as 500Å thick, a large difference in magnetic properties was shown between the films deposited after acid treatment and with no acid treatment. This was due to the difference in the microstructure of the films. Especially, highly crystallized parts appeared in the grain deposited after acid treatment. The films deposited after acid treatment had high perpendicular coercivity H_c(⊥). Such a high coercivity turned out to be due to these highly crystallized parts. The grain size was controllable with acid treatment which changed the density of active nuclei.

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Co-Cr and Co-Cr-W films were prepared by DC magnetron sputtering equipment on PET film. The dependence of magnetic anisotropy constants K_u1 and K_u2 on film thickness was determined from the torque curve measurement. When the film thickness is thin, the K_u1 is very small, and it increases rapidly as the thickness increases. On the other hand, the K_u2 is extremely large for thin films but as the thickness is increased, it decreases rapidly and approaches a nearly constant value. K_u1/K_u2 values are not constant. The dependences of φ₂ and φ₄ on film thickness were measured, where φ₂ and φ₄ were tilt angles of the easy magnetization axis from film normal for K_u1 and K_u2. The value of φ₂ was not equal to that of φ₄. These results suggest that there is another fourfold symmetry besides that of uniaxial anisotropy.

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Higher vertical coercivity of Co-Cr film is needed in order to obtain highr reproduced output. In this paper, we report how to obtain high vertical coercivity of Co-Cr film using PET film as the substrate. A low degree of crystal orientation in Co-Cr film yields a high vertical coercivity of the Co-Cr film. In double layer media, crystal orientation of Co-Cr layer is changed with that of permalloy underlayer. A high reproduced output was obtained up to 100 kBPI using the Co-Cr/permalloy double layer media with high vertical coercivity in the Co-Cr layer and a single-pole head. The inclination of the easy axis in a simple magnetic wall motion model or a rotation model cannot explain the increase in the vertical coercivity. The degradation of the orientation of the Co-Cr film may increase the Cr segregation in Co-Cr film, and then its vertical coercivity is increased.

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Co-Cr films were prepared on polyimide substrates with a temperature of T_s=27°C by rf sputtering method. Film thickness was varied from 0.2μ to 2μm. These films have low coercivity. When the c-axis orientation was good, the reentrant perpendicular hysteresis loops could be obtained. In these films, we observed domain patterns as a function of the thickness h and the c-axis orientation Δθ₅₀ by the Bitter method. The stripe domain and wall motion could be observed clearly in thick films with good c-axis orientation. The relations between the period of stripe domain D and h could be explained by wall motion. The dependence of h and Δθ₅₀ on the squareness ratio of in-plane hysteresis loop M_r(//)/M_s was studied. We calculated M_r(//)/M_s versus Δθ₅₀ and h based on a model assuming the μ* effect. Good agreement between the exprimental and calculated values was obtained.

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Sony Corp., Information Systems Res. Center A return path core of a single-pole thin film head for perpendicular recording was extended up to the top surface of the head in order to improve the reproducing sensitivity. In this type of head, as the gap length between the main pole and the return path core decreases, the reproducing sensitivity increases, while distortion of a reproduced waveform caused by a contour effect of the return path core increases. We developed a new head with waved edge of the return path core in order to reduce the distortion of the reproduced waveform. The waved edge was formed by the ion milling process. By simulation and experiment, the azimuth effect of the waved return path on recording characteristics, reproduced waveform and peakshift characteristics was investigated. The new head has high sensitivity, low distortion of waveform and small peakshift displacement.

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Miniaturization of the magnetic head core was sought aiming for wide band recording. To achieve this, core size effect and magnetic permeability effect on reproducing efficiency of the film core head was studied by both computer simulation and experiment. The main results are as follows: Minimum core width can be reduced to around 160μm without apparent decreasing of core efficiency; and core efficiency depends strongly on the permeability of the film core. Finally, the frequency characteristic of the FeAlSi film laminated core head constructed by these concepts was measured. The core loss ratio of 3.8 dB was gained between the frequencies of 2 MHz. and 18 MHz.

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Various metal-in-gap heads have been developed for the high density recording system. We report on a metal-in-gap head composed of a Mn-Zn ferrite core and FeGaSiRuO metal film which is prepared by sputtering, and in which the metal film is shown to run parallel to the gap-forming layer. In this type of head, the boundary between the metal and the ferrite usually acts as a pseudo-gap, resulting in a ripple in the playback output spectrum. It was found through experiments that some metal elements and oxygen contained in both the magnetic metal alloy and the ferrite diffuse around the boundary during the heating process. Due to the diffusion of these elements, nonmagnetic and less magnetic layers grow at the boundary and form a pseudo-gap. We suppressed the formation of these undesired layers by using FeGaSiRuO alloy having high B_s, thus remarkably reducing the ripple of playback output spectrum.

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An MIG mini-composite head for rigid disk drives which is composed of Fe-Al-Si thin film deposited on ferrite has been developed. The characteristics of the MIG head were studied and its magnetic field was calculated by FEM and compared with the ferrite head. Relation between the MIG head characteristics and the magnetic characteristics of Fe-Al-Si thin film was also studied. The magnetic field distribution at the trailing edge of the MIG head was found to be sharper than that of the ferrite head, indicating that the MIG head has high performance as a high density recording head. Output voltage of the MIG head with 1μm thick Fe-Al-Si film was low. The reason for low output was the low magnetic characteristics of the magnetic film.

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MR (magnetoresistive) heads, the characteristics of which do not depend on medium velocity, are superior to inductive heads at low medium velocity and high recording density. Because of the non-linear relation between applied magnetic field and magnetoresistance, second harmonic distortion occurs. In this study, dependence of the second harmonic distortion on peak shift and error rate was investigated. Intervals between zero cross points of a differentiated readout waveform on a two bit pattern were measured by a time counter. Error rate was calculated by peak shift and standard distribution on a zero cross point interval. Peak shift and error rate as a function of second harmonic distortion is considered using Gaussian distributed noise. It was found that calculations by Gaussian distributed noise correspond to the experimental data.

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The sensitivity of a magnetic read-out head using induced RF permeability change (active head) with NiFe/Al₂O₃ multilayered films has been investigated by measuring the output voltage response to magnetic fields, with film thickness and width as parameters. All thick multilayered films showed low coercivity and high permeability for a frequency of less than 50 MHz, though they showed a small decrease in induced RF permeability for about a 600 MHz frequency, even with a decrease in film width to 10 μm. The sensitivity increased by more than 10 times for all thick films, compared with NiFe single layered films, due to the improvement in softmagnetic properties and eddy current reduction.

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The paper describes a magnetic tape recorder for low frequency which uses a parametric reproducing head. The head is based on parametric oscillation in a resonant circuit comprised of a head and a variable capacitance in order to reproduce low frequency signals, which is difficult to achieve by conventional methods. The output voltage of the equipment is dependent only on the magnetic field of the input recording signal and is independent of the frequency of that signal. Consequently, the equipment has an output proportional to the input and a constant frequency response from zero to about 100 Hz. Here, the operation of the equipment is analyzed theoretically and good features are described.

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Domain structures of Co-Zr-Nb amorphous film for main-poles of single-pole type perpendicular magnetic recording head have been observed with the Bitter method. A narrower Co-Zr-Nb main-pole having lower H_k shows the disordered domain structure near the tip in the remanent state. It causes lower and unstable sensitivity of the narrow-track single pole head. The rotation magnetization of main domains works dominantly in the magnetization of a stable main-pole. A stable and highly sensitive single-sided single pole head is obtained by using a shorter main pole having the aspect ratio of about 1, which shows an ordered and stable domain structure even in the remanent state.

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Runout (dynamic deflection) of both a Co-Cr/permalloy flexible A disk and a commercialized particulate flexible B disk of 3.5'' diameter was studied using a disk drive with two pairs of two pads arranged in series to the disk rotating direction, and a photometric positioning sensor in place of a small sized head of the single pole type. In the disk drive, the radial position on the disk was varied between 30 and 37 mm at disk revolution rates ranging from 400 to 1200 rpm, to evaluate the effect of the pads' configuration on runout characteristics. Runout of A disk was controlled between15 and 30μm, while runout of B disk was over 60μm and almost unchanged. Stable read/write characteristics of A disk were observed in the high density region of 70 kfci under 1 gf head-pressure and runout of around 20 μm.

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A simulation study of the deformation of magnetic tape above the VTR drum using FEM has been carried out to investigate the tape flying characteristics. Reynolds' equation and the deformation equations of the tape are solved, taking into account the in-plane stress (i.e., geometrical nonlinearity). The validity of this simulation is checked by comparison with the experimental data. The following results are obtained by this simulation: 1) The flow of lubricant air from head window causes the tape to dip. 2) The dip enlarges above the rear of the window. 3) The dip becomes deep and long with increase of the length of the head window.

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Head field calculation of a single-pole type head was conducted to determine the effect of magnetic interaction between head and medium. We found that head field was influenced strongly not only by the magnetic properties of the backlayer but by those of the recording layer. We therefore clarified the relationship between the head field and the parameters of head and medium by our calculations, taking the magnetic properties of the recording layer into consideration. Moreover, a comparison of the head field between a single-pole type head and a ring type head showed that the former could obtain high density recording even with a relatively thick recording layer.

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The longitudinal magnetic recording process has been simulated by a super computer and compared with that of perpendicular magnetic recording. A curling incoherent magnetization reversal model and the statistical calculation of probable magnetization for magnetic particles in the interior of the magnetic layer of a medium have been introduced to the computer simulation. It has been theoretically confirmed by the computer simulation that the circular magnetization mode is formed in the medium at high desity recording and causes the recording demagnetizing loss, as we predicted qualitatively about twenty years ago.

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The influence of the thickness of a Co-Cr layer in a Co-Cr/Ni-Fe double layer medium on the recording and reproducing characteristics was investigated by computer simulation. In practice, the perpendicular media with a relatively thin Co-Cr layer, about 0.1 μm in thickness, but which is thicker than the longitudinal media, produce high reproduced voltage at high densities. The reason is that the sharp magnetic field distribution of a single-pole-head is created for a thin Co-Cr layer by enhancing the head-to-medium magnetic coupling. As a result, the large residual magnetization remains in the recording process, and the high resolution of the singlg-pole-head generates high voltage in reproduction, even at high densities.

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Possibility to decrease signal recorded noise of metal thin-film media by decreasing magnetic coupling between crystallites was studied with the following results. 1) Reverse DC erase noise is strongly related to signal recorded noise. 2) Reverse DC erase noise characteristics show a positive peak metal thinfilm media which have strong magnetic coupling between crystallites. 3) Contrarily, they show a negative dip particulate media which have weak coupling between magnetic particles. A Co-Cr thin-film medium and an isotropic anisotropy particulate medium are selected as a medium which has weaker magnetic coupling than a metal thin-film medium and a Co-γ sputtered medium with a peak in reverse DC erase noise characteristics, respectively. Reverse DC erase noise characteristics of these two media show a dip. As expected from the above results, signal recorded noise of a Co-Cr medium decreases slightly and that of an isotropic particulate medium also decreases as the recording density increases. Thus the possibility to decrease signal recorded media noise of metal thin-film media by decreasing magnetic coupling is confirmed.

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The relationship of the reproduced voltage and spacing in perpendicular recording is studied experimentally and analytically. Experimental results are obtained with a scale model of perpendicular recording enlarged 5,000 times, which simulates a single pole head and double layer medium system. In the analysis of the relation we extend Lopez's method to include the effect of the potential variation near the top of the main pole related to the variation of spacing. We obtained good agreement between experimental and analytical results.

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The photoinduced effect of this study is presented as the decrease ΔH_p of ferromagnetic resonance field of surface spin wave modes in an ion-implanted layer of YIG films during light irradiation. The H₂⁺ or He⁺-implanted films are annealed in a hydrogen atmosphere. The results with annealing show various behaviors of ΔH_p caused by implanted and diffused hydrogen, and the formation of large anisotropy in the surface layer of He⁺ -implanted films. Proposed models on the changes of chemical reaction between hydrogen and ferrous ion and the origin of the large anisotropy are discussed.

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A test chip using ion-implanted functions for a 16 M bit bubble memory device has been designed, fabricated and characterized. A new delineation process for ion-implanted tracks using SiO₂ ion-implanted masks is effective to reduce the defects in the minor loops. As a result, bias margin of 22 Oe was obtained for minor loop bubble propagation. The test chip operation with a wide-temperature range from −25°C to 80°C has been realized.

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Ion-implanted tracks with 1.5μm period for 64M bit magnetic bubble memory devices have been fabricated and operated. The bubble material used here is (BiSmLu)₃(FeAl)₅O₁₂ garnt film supporting 0.45μm bubbles. The resist mask patterns for implantation were formed by a 1/10 reduction projection aligner using rectangular patterns on a reticle. The bubble propagation tracks were fabricated by double deuterium implantation and annealed at 400°C for 30 min with a SiO₂ layer deposited on the garnet surface to stabilize the implanted layer. More than 7% operating bias field margin was stably obtained in quasistatic bubble propagation. This shows that the ion-implanted devices have great potential for 64M bit magnetic bubble memory devices.

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Effects of spin-orbit interaction (S.O.) and S₄ low symmetry crystal field on the Faraday rotation spectra (FRS) of the tetrahedral Co³⁺ in magnetic garnets are investigated in the scheme of the crystal field theory. The FRS of the magnetic garnets containing tetrahedral Co²⁺ and Co³⁺ are also calculated. In order to explain the observed FRS of the tetrahedral Co³⁺, (1) the coefficient λ of S.O. having negative sign in the -100∼-160 cm^-1 range, and (2) a fairly large low-symmetry field are required.

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The optical absorption loss a and Faraday rotation θ_F in the wavelength region λ=0.5∼2.5μm are investigated for YIG films incorporated with a small amount of Pb, Ca and other ions. The contribtuions of pb²⁺, Pb⁴⁺, Fe²⁺ and Fe⁴⁺ ions to α and θ_F are studied by reducing the Ca-free and Ca-droped YIG films grown by LPE method. It turns out that the absorption enhancement due to Pb²⁺ is remarkable near the optical absorption edge, and that due to Pb⁴⁺ is remarkable at λ∼0.56μm. The strong absorption at λ∼0.56μm is thought to originate in the combined presence of Fe³⁺ and Pb⁴⁺. As for the Faraday rotation, it is found that the contribution by Fe⁴⁺ is negative in the θ_F spectra in the near infrared recion like that bv Pb²⁺, while the Fe²⁺ contribution is negligible in the measured wavelength region.

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Optical absorption and Faraday rotation of bulk single crystals of R_3-xBi_xFe₅O₁₂ (R=Gd, Tb, Dy, Ho, Y, Er, Tm, Yb, Lu) were measured in the wavelength range of 0.7 to 1.1μm. The peak position of the broad absorption band located at ∼0.9μm shifts to the higher energy side with the increasing size of R ion, at the rate of -0.27μm/Å. Therefore, the absorption at a given wavelength near 0.8μm, the valley between two broad absorption bands located at ∼0.7μm and ∼0.9μm, can be minimized by the choice of R of a proper size. The magneto-optical figure of merit of Lu_2.2Bi_0.8Fe₅O₁₂ is 13 deg/dB at 0.83μm, and that of Gd_2.2Bi_0.8Fe₅O₁₂ is 24 deg/dB at 0.78μm.

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Magnetization reversal in Bi−Ga-substituted YIG film rectangular patterns, formed by micro-lapping and subsequent acid etching, is based on the nucleation and extent of reverse domains. As the pattern size decreases from 300×300μm to less than 100×100μm, nucleation field (H_n) increases from 100 to 530 Oe which is equal to the anisotropy field. To control the H_n, an artificial magnetic defect is formed in the center of the pattern by focussed ion-beam implantation. When Ge- or Si-ions are implanted at 50 keV in a spot 0.3μm in dia., H_n drops less than 330 Oe. As the Ge-ion implanted area extends, H_n decreases gradually. Assuming the ion-implanted region is a reverse domain nucleus, H_n is calculated as the external field where the maximum of total magnetic energy is attained. The theoretical values of H_n agree well with the experimental ones.

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Theoretical investigation has been performed on the Faraday effect of Cd_1-xMn_xTe epitaxial films prepared by ionized-cluster beam deposition technique. Splitting energies and oscillator strengths of an exciton level are calculated by taking account of a nondegenerate second order perturbation. The wavelength dispersion of the calculated Faraday rotation spectra is compared with the experimental data of Cd_1-xMn_xTe films. This suggests that the Faraday rotation is closely related to the magnetooptical transitions to Zeeman splitting levels of exciton.

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Artificial superlattice of Co-(Pr, Nd) was fabricated on glass substrates using the electron beam evaporation technique. Magnetic properties such as (i) the dependence of saturation magnetization, M_s, on temperature, (ii) the dependence of perpendicular magnetic anisotropy constant, K_⊥, on temperature and (iii) the dependence of polar Kerr rotation angle, θ_k, on wavelength were systematically investigated. For Co/Pr, Co/Nd artificial superlattice, rare earth atoms within 25Å of the interface were found to be coupled ferromagnetically with Co atoms at 77K. K_⊥ increases with decreasing artificial period, D, for both Co/Pr and Co/Nd artificial superlattice. The maximum values of K_⊥ at 77K are 10×10⁶ erg/cm³ and 4×10⁶ erg/cm³ for Co/Pr and Co/Nd artificial superlattice, respectively. The wavelength where the minimum θ_k is observed shifts from 0.45μm to 0.65μm with decreasing artificial period.

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Magneto-optical properties of Fe-F, Co-F and Ni-F films have been investigated. The films were produced by rf-sputtering using compressed powder targets of FeF₃, CoF₃ and NiF₂. The structure of films was confirmed to be amorphous, containing a small amount of crystalline fluoride. Some of the films showed perpendicular magnetic anisotropy, high coercivity (600∼2000 Oe), fairly high remanence ratio (∼0.7), and saturation magnetization of 5∼50 emu/g. The films also exhibited Faraday rotation coefficient of ∼10⁴ deg/cm in low wavelength range and depended smoothly on wavelength for 500∼2000 nm. Optical absorption coefficient was also at the level of∼10⁴ cm^-1 for 400∼1500 nm. Both Kerr rotation angle and reflection spectrum varied depending on wavelength in the transparent films. The electronic structure of films was measured by soft X-ray spectroscopy and thought to be in an interme-diate state between metallic and compound states.

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A study on rf sputtering plasma of Co, Gd pure metals and Gd₂₆Co₇₄ alloy with optical emission spectroscopy (OES) is performed under various discharge conditions such as argon pressure P_Ar, taget voltage V_rf and substrate bias voltage V_b. From the measurements of OES line intensities and deposition rates in various P_Ar, V_rf and focussing field H, it is found that the line intensity of both Co and Gd atoms is represented as a linear or square function of the atomic densities in the plasma. Moreover, the preferential resputtering effect of Gd atoms is also confirmed from the change of the line intensity under the condition of negative bias voltage | V_b | ≥20V.

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Magneto-optical contribution of Nd in vacuum evaporated Nd-(Fe, Co) films has been investigated by measuring the wavelength dependence (λ=250∼800 nm) of Kerr rotation (θ_K), together with the spectra of photoelectrons emitted under X-ray (XPS). The Kerr rotation for Nd-Co films increases with decreasing λ when Nd concentration is over 14 at.% and shows a peak at 300 nm, while the Kerr spectra of Nd-Fe films become flat with increasing Nd content. The compositional dependence of Kerr spectra for Nd-Co and Nd-Fe films is characterized by the following two factors, 1) the contribution of Nd to θ_K at short wavelength, and 2) the differences of the Kerr spectra between crystalline and amorphous states of Co or Fe. The XPS intensity for Nd-Co and Nd-Fe shows a maximum at about 4.2 eV below the Fermi level, which corresponds to the peak of θ_K at 300 nm. In pseudobinary system Nd-(Fe, Co) films, θ_K is larger than any other binary system with the same Nd composition in the entire wavelength region, and Nd₂₂(Fe₆₅Co₃₅)₇₈ film shows θ_K of about 0.58° at 300 nm.

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Exchange coupled double-layered TbFeCo films, which consist of a transition-metal dominant 1st layer and a rare-earth dominant 2nd layer, are found to be a high performance medium for an erasable optical memory disk. In this paper, we have studied the dependence of recording characteristics on the magnetic properties of each layer. The temperature dependence of switching fields of each layer was measured by Hall effect, and the change in magnetization process with temperature was discussed. It is suggested that the recording noise of large H_c1 (coercive force of the 1st layer) film at lower write power results from a difference of the magnetization process on recording temperature.

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This paper presents a new design of magnetooptic pick up which detects the phase shift of circular polarized light instead of the rotation of plane polarized light. The use of a polarizing beam splitter and a quarterwave plate allows theoretically 100% efficiency. Efficiency is important not only in order to reduce the laser power when recording but also to avoid the reflected light which would interfere with the output of the laser. We discuss the theory of circular polarized readout and describe on experiment on reading a rare earth iron garnet magnetooptic disk. In conclusion, we discuss the advantages and drawbacks of such a reading method.

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To develop Nd-Fe-B permanent magnets suitable for radial or circumferential applications, such as a stepping motor, a hot extrusion method was utilized. The extrusion was applied to billets produced by hot-pressing rapidly quenched powder. A planeanisotropic magnet was obtained by forward extrusion and a radial-anisotropic magnet by backward extrusion. The respective magnetic properties of these magnets in the radial direction were as follows: B_r=0.895 T, _iH_c=860 kA/m and (BH)_max 134 kJ/m³ for the former, and B_r=1.065 T, _iH_c=520 kA/m and (BH)_max=183 kJ/m³ for the latter.

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In melt-spun ribbons of (Pr, Dy)₁₅(Fe, Co,)₇₇(B, C)₈ alloys prepared by the single roller method, the effects of C substitution for B, Co for Fe and Dy for Pr in Pr₁₅Fe₇₇B₈ alloy, substrate surface velocity and subsequent annealing on the magnetic properties were studied, and their bonded magnets were made of the optimum-quenched ribbons. The maximum energy product of 98.3 kJ/m³ was obtained for Pr₁₅Fe₇₇B₈ ribbon prepared at a substrate surface velocity of 11.8 m/s. In (Pr, Dy)₁₅(Fe, Co)₇₇(B, C)₈ ribbons, we confirmed that the best maximum energy product of 96.4 kJ/m³ was obtained for (Pr_0.95Dy_0.05)₁₅(Fe_0.9Co_0.1)₇₇(B_0.5C_0.5)₈ alloy which contains Dy and Co to improve the temperature dependence of B_r and H_CB. X-ray diffraction patterns from samples with the highest coercivity showed a mixture of an amorphous and a fine crystalline phase. The best magnetic properties obtained in these bonded magnets of (Pr_0.95Dy_0.05)₁₅(Fe_0.9Co_0.1)₇₇( B_0.5C_0.5)₈ alloy were (BH)_max=64.9 kJ/m₃, H_CJ=1400 kA/m, H_CB=419 kA/m, and B_r=0.62 T. It was known that the temperature dependence of B_r and H_CB for (Pr, Dy) -(Fe, Coi)-(B, C) bonded magnets was superior to those of Pr-Fe-B bonded magnets.

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This experiment was carried out to investigate the effects of composition and annealing condition on the magnetic properties of the isotropic cast (Pr, Dy)-(Fe, Co)-(B, C) alloys. Compositions were Pr₁₅Fe₇₇B₈, Pr₁₅(Fe_0.9Co_0.l)₇₇(B_1-xC_x)₈ and (Pr_0.95Dy_0.05)₁₅(Fe_0.9Co_0.1)₇₇( B_0.5C_0.5)₈. In Pr₁₅(Fe_0.9Co_0.1)₇₇(B_1-xC_x)₈ alloys, the value of H_CJ increased with the increase of C substitution for B from x=0 to x=0.5. In these cast alloys, (Pr_0.95Dy_0.05)₁₅(Fe_0.9Co_0.1)₇₇(B_0.5C_0.5)₈ alloy after annealing 5 h at 800°C showed the best magnetic properties, (BH)_max=38.4 kJ/m³, H_CJ=392 kA/m, H_CB=248 kA/m and B_r=0.54T. From EDX analysis, it was known that this alloy consisted of two phases, (Pr, Dy)-rich phase and (Pr, Dy)₂(Fe, Co)₁₄(B, C) phase.

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The concentration and temperature dependences of coercive force have been studied on Fe-Sm and other Fe-rare earth (R)a morphous alloys prepared by sputtering. The coercive force of Fe-Sm amorphous alloys shows a large concentration dependence as expected from the random anisotropy model. The temperature dependence of coercive force shows a linear relationship between log H_c and T, and it is composed of two straight lines in the ferrimagneticlike amorphous alloys. The magnitude of coercive force of Fe_66.7R_33,3 amorphous alloys depends on the second order electrostatic field except for that of Fe-Ce.

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The effect of annealing on the generation and detection characteristics of magnetoelastic waves (MEWs) is studied in Fe_77.5Si_7.5B₁₅ amorphous wires. Annealing after wire-drawing is found to be exceedingly effective in improving the efficiency in a high frequency region. The wire-drawing is indispensable to get rid of inhornogeneities which may scatter the high frequency MEWs. The annealing is necessary to soften a magnetic hardness arising from the wiredrawing. It is found that a partial annealing develops a highly sensitive small region to a driving magnetic field in the sample wire which is made insensitive to the driving field by a wire drawing. This small region serves as an excellent source which is preferable to generate high frequency MEWs.

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The recent development of the numerical analysis of magnetic flux in electrical machines has given rise to a need for an accurate expression of the magnetic hysteresis process in core materials. In this investi- gation the idea of the Everett function, which is an integral form of the Preisach density function, was applied to simulate the hysteresis curves of practical core materials. The Everett function of various core materials was measured using a microcomputer- controlled hysteresis tracer and a mathematical for- mulation of the function was obtained. The formula can predict the hysteresis curves of the materials with good accuracy.

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Magnetic properties were measured on Co-Si-B amorphous wires with negative magnetostriction prepared by in-rotating water quenching technique and results were compared to those of Fe wires with positive magnetostriction. The Co wire was found to exhibit the large Barkhausen discontinuities as well as Matteucci effect similar to the Fe wire. It was also found that the Co wire shows a bamboo-like domain pattern at the surface and has a reverse domain propagation mobility larger than the Fe wire.

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New reinforcement methods are introduced for the large Barkhausen and Matteucci effects in amorphous magnetostrictive wires. Cold-drawn and then torsion annealed (CDTA) wires (Fe_77.5Si_7.5B₁₅, 50 μm diameter) generate ac pulse voltages, e'_p, (Matteucci voltage, for short) of 35∼75 mV between the two ends of 200-mm long wires for 2 Oe, 60 Hz external fields. The critical wire length, l*, for the large Barkhausen (LB) effect is about 25 mm, which is useful for construction of small sized field sensors. The critical field, H*, for LB effect is 0.3∼0.9 Oe. The value of e'_p/l* of the CDTA wires is more than 200 times that of as-prepared 125μm diameter wires. Magnetoelastic wave propagation characteristics are also remarkably improved in the CDTA wires.

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Magnetic properties of narrow stripe Co-Ta-Zr amorphous films with induced anisotropy across the stripe width have been investigated. Permeability of the films decreases with a decrease in the stripe width. This can largely be explained by the increased demagnetization field which may reduce the initial anisotropy and rotate the easy axis to the direction perpendicular to the initial easy axis, or change the magnetic domain structures. Film stress may act positively or negatively on this, depending on the film's magnetostriction constant. It is, therefore, essential to determine an appropriate magnitude of induced anisotropy and to choose a proper combination of magnetostriction constant and thermal expansion coefficient of the substrate. Utilizing this knowledge, thin film heads with 5μm track width have been fabricated. Reproduced voltage of 380μVpp/mm · turn · m/s has been obtained when operated with Co-Cr perpendicular recording medium.

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The magnetostriction of Fe_1-xY_x (0.2≤x≤0.6) and (Fe_1-x-Co_x)_0.8Y_0.2(0≤x≤0.6) alloys has been measured in the temperature range from 20 to 300 K. In FeY alloys, the magnetostriction λ is 2.8×10^-6 at 20K for x=0.2 and shows a monotonic decrease with increasing x and temperature; this magnetostriction of the Fey alloys is the smallest in the Fe-based amorphous binary alloys investigated so far. In (Fe_1-x-Co_x)_0.8Y_0.2 alloys, λ at room temperature shows a minimum of 1.0×10^-6 at x≈0.3, where the magnetization and coercive force are 125 emu/g and 0.05 Oe, respectively.

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Magnetooptical effect of magnetic fluids is investigated. The phase difference θ between the ordinary ray and the extraordinary ray which are transmitted through the magnetic fluid thin film was found to be described in the functional form θ₁f(H)/[T-T₁+f(H)], where H is the magnetic field applied to the magnetic fluid thin film, T is the absolute temperature of the film, f(H) is a certain increasing function of H and T₁, θ₁ are the positive constants. The field dependence of light transmissivity of magnetic fluid thin films is well described by the cluster model of ferrous colloidal particles in the applied field direction when the aggregation is small. The field dependence of transmissivity is, however, interpreted neither by the electric absorption of the clusters nor by the Rayleigh scattering when the cluster becomes larger. The diffraction effect by the linear clusters directed to the applied field must be taken into account in interpreting the light extinction.

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Temperature dependences of magnetocrystalline anisotropy constant K₁ and magnetostriction constants λ₁₀₀ and λ₁₁₁ were measured for Fe-Si-Al alloy single crystals annealed at 1200°C or quenched from 1200°C around the composition region 4∼6 wt%Si, 2∼5 wt%Al, bal. Fe. The crystal structure of these single crystals was determined by electron diffraction. The large difference in the magnitude of K₁=9.1×10³ erg/cm³ for 4.8 wt% Si, 5.0 wt% Al, bal. Fe alloy and K₁=1.1×10⁵ erg/cm³ for 4.7 wt%Si, 3.8 wt%Al, bal. Fe alloy at room temperature was found to be connected with the difference in their crystal structures. The lines of λ₁₀₀=0 and λ_S=0 were determined as a function of composition. The concentration of second peak alloy for μ_m locates along the line of λ₁₀₀=0. Moreover, the second peak alloy may have the D0₃ structure.

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