A read/write simulation based on the Poisson equation by a finite element method was performed on keepered media (KM) with a thin soft magnetic layer (keeper layer) under a recording layer and a thin-film head. An extendedn Stoner-Wohlfarth (SW) model was used for the recording layers, in witch the switching rate of each SW particle at finite temperatures is taken into account using the Neel-Arrhenius law and the master equation.Thermal stability of the medium was estimated by the recorded magnetizations and the corresponding output voltage waveforms for 423 kBPI calculated at 300 K as a function of time t after the recording. Although the output voltage of the KM was slightly less than that of the conventional medium due to magnetic flux circulation through the keeper layer, the output voltage reduction rate due to thermal fluctuation decreased remarkably with a thin keeper layer.

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A finite element read/write simulation was performed by solving the Poisson equation for a two-dimensional model of an antiferromagnetically coupled magnetic medium (AFC medium) and a thin-film-head system. The AFC medium is composed of two recording layers and a thin intervening Ru layer. From the simulation of an isolated transition, we found (1) the output waveform at t = 0 s has a shoulders on the tail of the main peak corresponding to the extra transition in the bottom recording layer. However, the shoulder becoms small at around t = 10^-7 s, and disappears completely at t = 10¹⁰ s, (2) An antiparallel magnetization alignment in a bit is produced by thermal energy as well as a reverse field to write the transition. From the simulation at 423 kFRPI, it was found that (3) an antiparallel magnetization alignment in a bit is established in the write process by a reverse field to write the bit. Furthermore, from thermal stability estimation, we found that (4) the time needed to be an antiparallel magnetization alignment in a bit lengthens with the increase of the bottom layer coercive field H_c and with the decrease of the interlayer antiferromagnetic exchange constant A. (5) The output voltage reduction curves at around t = 10¹² s depend greatly on A and H_c. (6) The thermal stability of the AFC medium is improved by an order of magnitude in time scale compared with that of the conventional medium.

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This paper provides a microstructure model for perpendicular recording media based upon magnetic clustering, taking into account the size variation. We discussed comparisons between experiments and calculations based on the model for the saturation tendency of the experimental medium noise and confirmed validity of this model. With this model, both mean cluster size and standard deviation can be estimated from experimental read/write characteristics. The estimation shows that the cluster size deviation of current perpendicular recording media is somewhat larger than that of longitudinal recording media. The significance of the cluster size variation is pointed out.

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The perpendicular stray field from the tracks neighboring the center track in a perpendicular SPT head/double-layer medium system was investigated using a 3D read/write simulation system in witch the Poisson equation for the head/medium system is solved by the edge-based finite element method. The main results were as follows: (1) the stray field in the double-layer medium is about two times greater than that in the single layer, (2) the stray field under the main pole or the auxiliary pole in an SPT head as a function of the relative permeability μ_r of a soft underlayer (SUL) initially increases, reaches a maximum at around μ_r = 10, and decreases monotonically with increasing μ_r, (3) the stray field for SUL μ_r greater than 10 is increased by cutting tha SUL into short tracks, and (4) the stray field is almost independent of the thickness of the SUL when μ_r is greater than 100.

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The magnetization process in Co/Pd multilayers under a tilted magnetic field was studied using ferromagnetic Hall effect analysis. The loci of the tip of an effective magnetization vector were determined from the simultaneously detected anomalous and planar Hall voltage signals contributed by the perpendicular and in-plane magnetization components, respectively, inside a multilayered specimen. The evaluated magnetization reversal process exhibited a clear dependence on the multilayer structure due to the variation of the Co or Pd layer thickness. For different types of multilayers, Hall effect study under a tilted magnetic field revealed the difference in the magnetization reversal phenomenon, while no significant difference was detected in the characteristics measured in a perpendicular applied field.

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Co-Pt thin films were prepared on glass substrates by gas flow sputtering (GFS), and the relationship between the magnetic properties and film structures was studied. GFS is a high pressure sputtering in the range of 100 Pa, which enables low-temperature and soft film growth to occur. It was found that the coercivity of Co-Pt films with a thickness of 30 nm increased with increasing Pt content and took high value of over 4 kOe at Pt contents of about 20 at%, and also found that films with Pt contents less than 30 at% were of hcp structure and composed of small grains about 5 nm in diameter. A high coercivity observed in these films was assumed to be due to their grain structure, consisting of small hcp-Co-Pt crystallites surrounded by more oxidized boundaries.

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In perpendicular magnetic recording, the major concerns are transition position jitter, which is the dominant noise source, and magnetization transition width or transition parameter, which affects readback pulse width. Thus, these parameters restrict attainable linear density. Their influence on error rate performance was investigated with numerically synthesized waveforms and a software channel. Calculated error rate shows that transition jitter restricts the bit error rate (BER) for small pulse widths. However, when the pulse is wide, it causes BER degradation by system noise emphasis during equalization. Assuming a target density of 200 Gb/in², with linear density of 1200 kFCI, a transition jitter of 1.6 nm and transition parameter of 20 nm are a compromise. In this case, 2% resolution is estimated at the linear density of 1200 kFCI for a read gap of 60 nm and magnetic spacing of 15 nm.

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The head field strength for saturation recording was investigated with the assistance of a simulation to determine the head field. The saturation field was defined as the minimum write field that gave an overwrite erasure of − 30 dB. A strong correlation between the medium coercivity and the head field for saturation was revealed. Head fields required to saturate the media were between 1.3 and 1.5 times larger than the H₀ of the media. With a CoPtCr-SiO₂ medium, the head field for saturation was almost 0.7 times the anisoropy field.

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We designed and fabricated new flying heads with pico-sliders for cylindrical magnetic storage and evaluated read-resolution and flying height. A one-pad slider for a cylindrical medium fabricated in this study has only small trailing pad formed on the trailing edge of the slider. We clarified the relation between the length of the trailing pad and its flying height. The envelope of the head output did not show any modulation, large spike pulse, or thermal asperity associated with contact with the cylindrical medium. The D₅₀ values increased as the designed flying height decreased, i.e. as the length of trailing pad decreased. The relative flying height, derived by calculating the spacing loss factor, showed good quantitative agreement with designed flying height. The results mean that read-resolution, i.e. flying height, is improvable by appropriate design of the ABS structure of the head-slider for cylindrical media.

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Magnetic tunnel junctions using half-metallic La_0.7Sr_0.3MnO₃ (LSMO) were investigated. Two types of junctions, Co/SrTiO₃(STO)/LSMO (CSL junction) and LSMO/STO/LSMO (LSL junction) were prepared, where the Co layer on the STO layer of the CSL junction was grown at room temperature and the LSMO layer on the STO layer of the LSL junction was grown at 500°C or 700°C. The observed TMR ratios for CSL and LSL junctions were 50% and -4%, respectively. The junction resistance of CSL increased exponentially with increasing STO thickness (t_STO), whereas that of LSL was almost independent of t_STO. It was found that the low TMR ratio of LSL was due to the inferior quality of the STO layer, caused during the growth of LSMO on the STO layer in an Ar atmosphere at high temperature. The inferiority of the STO layer-that is, introduction of defects into the STO layer- causes a decrease in the junction resistance and affects the decrease in the spin polarization of the upper LSMO layer, and subsequently results the small TMR ratio.

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A process for fabricating small magnetic tunnel junctions (MTJs) by using focused ion beam (FIB)-assisted chemical vapor deposition was investigated. Deposited tungsten was used as an electrode, and deposited carbon was used as a mask. MTJs with a junction area of 3 × 3 μm² showed a TMR ratio of about 30 % at room temperature.

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We investigated the structural and magnetic properties of Co₂MnAl thin films with Cr buffer layers, and the tunnel magnetoresistance (TMR) effect of junctions using Co₂MnAl Heusler alloy. The saturation magnetization of Co₂MnAl film deposited at 350°C was 711 emu/cm³ which was almost the same as that reported for bulk. The maximum TMR ratio of the junctions was 12% at room temperature and 26% at 25K. TMR ratio increased to 17% at room temperature after annealing at 200°C for one hour.

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The structural and magnetic properties of Co₂MnSi thin film grown by the ion beam sputtering method were investigated. Films grown on glass substrate at temperatures from 300°C to 600°C were polycrystalline, as were films grown on Si(100) and MgO(100) substrates at 600°C. The crystalline quality of the film improved with increasing substrate temperature. Film grown at 600°C showed the largest magnetization near the bulk value. On the other hand, film with the preferred orientation to the (001) plane was obtained by growing a Ta buffer layer before the growth of Co₂MnSi film on any substrates. The saturation magnetization increased with the increase of substrate temperature. This fact is considered to be due to the increase of the long-range order parameter.

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Insulator layers of Nd₂CuO₄ (NCO) and Ba_0.4Sr_0.6TiO₃ (BSTO), which have a good lattice matching to SFMO, were epitaxialy grown on SFMO by magnetron sputering in different preparation atmospheres (Ar, Ar+H₂, Ar+O₂). The quality of SFMO was evaluated by measurement of magnetization and crystal structure. We suggest that insulator materials having a small misfit to SFMO and the same preparation condition (Ar+H₂) as SFMO are suitable as insulators of TMR junctions. We also demonstrated the hetero-epitaxial growth of SFMO/NCO/SFMO trilayers.

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We succeeded in creating a partial nonmagnetic area in magnetic 0.65C-13Cr-Fe alloy. This ‘dual state magnetic material’ is expected to separate magnetic design from mechanical design for ideal magnetic parts. A material for automoive use must be able to withstand temperatures below -40°C. To use dual state magnetic material as an automotive part, it is necessary to find an appropriate method to obtain a steady state down to -40°C. We performed heat treatment with parameters of heat treatment temperature and heat treatment time. By measuring magnetic permeability and microscope images, we found that a heat treatment temperature of 1200°C and heat treatment time of 2 min. is the most appropriate condition. With a heat treatment temperature of 1100°C, permeability is not low enough to be considered nonmagnetic.

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Magnetic field sensors such as flux gate and magnetoimpedance elements have been sonsidered to be useful tools for indicating the direction of a terrestrial field. Downsizing of these sensors is essential for then to be used in highly integrated electronic devices such as mobile phones and computers. We developed a new type of magnetic field sensor that has a great advantage in this respect. The sensor has a composite structure cosisting of a mechanical resonator with a high Q factor and magnetostrictive layers. With the high sensitivity of the magnetostrictive layers to external fields, the resonance frequency of the resonator is expected to be shifted by the ΔE effect. Since the shift in frequency is independent of the resonator size, appreciable downsizing of the sensor is possible. In this paper we describe our initial experiments to verify that the composite resonator is sufficiently sensitive to detect terrestrial fields. The results show that it has a sensitivity of 40 Hz/Oe for a resonator with a resonance frequency of 120 kHz.

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A micromachined magnetoimpedance (MI) element was developed and its MI properties were investigated. Consisting of a SiN/Al/NiFe/SiO₂ film, it was prepared on a Si (100) wafer and fabricated by photolithography and etching. Ni₈₀Fe₂₀ film with nearly zero magnetostriction prepared by bias magnetron sputtering under a magnetic field was adopted as a magnetic layer in the MI element, and magnetic anisotropy was induced parallel to the current direction. Sensitivity corresponding to the maximum fractional change in impedance increased with thickness and length, and was greatest for a width of 20 μm. The values for whick the MI element had the best properties were 38 % for the sensitivity, 1446 ppm/°C for the temperature coefficient of impedance and 712 ppm/°C for the temperature coefficient of sensitivity. These values were much better than those of conventional magnetoresistance (MR) sensors. Therefore, these micromachined MI elements have great potential for use in integrated magnetic sensors.

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Recent requirements for voltage regulators in mobile apparatus have included small size, thinness and low power dissipation. We have developed a new dc-dc converter module which includes a microinductor using CoFeSiB/SiO₂ multilayer film and a control IC with dimensions of 6.0 × 6.0 × 1.0 mm³. Characteristics are an input voltage from 3.0 V to 5.0 V and an output voltage from 0.8 V to 4.8 V. This converter module has achieved a maximum efficiency of about 92% and 70% at output voltages of 2.0 V and 0.8 V, respectively.

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A switched reluctance motor (SRM) has such desirable features as simple construction, high reliability, and low cost. The SRM has not, however, been put into wide application because of large torque ripple and acoustic noise. In addition, quantitative analysis and optimum design of the SRM have not been fully charified. In a previous paper, we proposed a simple magnetic circuit model of an SRM based on its configuration. We calculated such dynamic characteristics of the SRM as excitation voltage, winding current, and flux in each part of the motor. In this model, however, reluctance of the stator and rotor cores are approximated by a linear function. In order to improve the calculation accuracy, we have to consider nonlinear characteristics of the core material. Furthermore, local saturation occurring at stator and rotor pole-tips and leakage fluxes from the stator pole must be considered. In this paper, we examine a nonlinear magnetic circuit model of the SRM considering the local saturation at the pole-tips and the leakage fluxes.

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This paper describes iron losses segment cores made of grain-oriented (50ZG) and non-oriented (50H350) silicon steels. The segment core shape does not make the magnetic flux distribution uniform, and the induction frequency makes it difficult to calculate the core loss in both materials. In the segment core of grain-oriented silicon steel where the rolling direction is parallel to the yoke in the segment, the core loss is lower than in the segment core where the rolling direction is parallel to the teeth. It is also lower than that in a core made of non-oriented silicon steel at 1.5 T and 50 Hz.

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Magnetic circuit methods make it possible to analyze characteristics of various magnetic devices by simple calculations. Furthermore, we can use general-purpose tools, such as a SPICE circuit simulator, for calculation. In a previous paper, we proposed a method for calculating iron loss characteristics based on a magnetic circuit model considering iron loss. However, since this method treats hysteresis loss and eddy-current loss collectively, it is necessary to vary the parameters of the magnetic circuit model when frequency is varied. In this paper, we propose a method for calculating iron loss for each frequency without varying the parameters of the magnetic circuit.

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An interior permanent magnet synchronous motor (IPMSM) has high efficiency and torque because the motor utilizes both magnetic torque and reluctance torque, because of the locations of permanent magnets in the rotor. The IPMSM has many applications, such as in electrical household appliances, in office automations and in electrical vehicles. Establishment of the optimum design for an IPMSM is thus important. Here, we present one calculation method for the dynamic characteristics of an IPMSM with concentrated winding based on the magnetic circuit model. In this model, the magnetic circuit of the IPMSM is expressed by variable reluctance and permanent magnet magnetomotive forces (MMFs) changing with rotor angle. In order to obtain the reluctances and permanent magnet MMFs, we calculate fluxes passing through a stator pole using the finite element method (FFM). Using the proposed model, we can easily calculate dynamic characteristics of the IPMSM.

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In most wire communication systems, communication lines are also used as power lines. Therefore, the powered terminal needs to separate as communication signals and dc supply power in its input Well-known separators usually utilize a combined circuit of inductors (or transformers) and capacitors. When the lowest frequency of the signal is low, the inductance bocomes high and the size of the inductor increases. A conventional electronic choke circuit with no inductor has the disadvantages that power dissipation is high and the dc current is limited to unidirectional flow. Our original communication system consists of low-power dc-dc converters. Because a converter in the powering terminal operates not only as power supply but also as transmitter, it is preferable that the electronic choke be bidirectional. In this paper, the ac voltage attenuation characteristics of a new low-loss electronic choke with small inductors and an amplifier are investigated by experiment and analysis.

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Switched reluctance motors (SRMs) have such desirable features as simple construction, high reliability, and low cost. Characteristics of the SRM differ with the excitation timing or period even if the SRM is operated at the same source voltage, because motor torque depends on gap reluctance, which changes timing of SRMs have been reported in many papers. On the other hand, no examination of excitation direction has been reported. Furthermore, combinations of excitation direction in each phase also have not been investigated. In this paper, based on a finite element analysis, we examine the effects of an excitation direction on characteristics of the SRM.

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In previous studies, we examined a magnetic micro-machine composed a magnet and spiral structure. As the magnet was magnetized in the diameter direction, the micro-machine rotated in synchronism with the rotating magnetic field. This time, we fabricated two types of spiral magnetic micro-machines. One had the magnet and the wire of the spiral structure (head type). The other had the wire of the spiral structure (spiral type). We examined the influence of the micro-machine length. As a result, we found that the swimming velocity of the head type micro-machine depended on the machine length. The swimming velocity of the spiral type micro-machine does not depend on the machine length.

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We produced a clutch prototype using MR (magnetorheological) fluid free from particle sedimentation. A thixotropic carrier fluid consisting of the mixture of Di-2-ethylhexylphthalate and synthetic smectite is proposed in order to solve the sedimentation problem usual in MR fluids. The new MR fluid was utilized in the clutch produced experimentally, and the clutch performance was examined by measuring the relationships between transmitted torque and dc applied magnetic field. The clutch torque can be controlled actively by changing intensity of the magnetic field.

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We measured bilateral somatosensory evoked fields (SEFs) by electrically stimulating the right thumb of four subjects, using a three-dimensional second-order gradiometer connected to 39-channel SQUIDs, which can detect magnetic field components perpendicular to the scalp (Br) and tangential to the scalp (BΘ,BΦ).
In order to assess the relation between phase lag and stimulus repetition frequency (SRF), we detected the delay time of a component synchronous with stimulation interval (27 to 501 ms) by convolution of the reference and SEF wave (15-40 Hz, BPF).
The phase lag of contralateral hemisphere was linear to SRF for at least two different SRFs in all components, but the phase lag of the ipsilateral showed a slope for some SRFs in all components. It was tested for significance of the linear regression slope (β≠0, P<0.05).
A simulation study for phase lag was carried out with ipsilateral hemispheres. It was concluded that response latencies calculated by using the slope of each component corresponded to the SEF latencies.

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We measured magnetocardiograms (MCGs) of a normal subject and a Wolff-Parkinson-White (WPW) syndrome patient. It is generally difficult to separate the accessory pathway and normal conduction system by visualization of the current density distribution (VCDD), because the VCDD has a wide range. Independent component analysis (ICA) is a useful method for separating independent signals from overlapping signals. In this study, the source of the accessory pathway was estimated by using ICA to obtain the VCDD.
First, principal component analysis was applied to the MCG as a pre-process and ICA was performed on the same dominant components. The activity of the accessory pathway was extracted from these components, and the waveform was reconstituted.
The VCDD was displayed from the onset of the delta wave (150 ms) to the R wave region (220 ms). The positions of the current density (a) without the ICA and (b) with the ICA were particularly different at 160 ms and 180 ms. The current density with the ICA remained in the same position, D5, from 160 ms to 220 ms, and was also about 2 cm different from the current density without the ICA.
It was confirmed that ICA is useful method for estimating the VCDD of an MCG of a WPW syndrome patient.

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Conductivity tensor images of a rat’s brain were obtained by a method using diffusion-weighted magnetic resonance imaging (MRI). Signal attenuations in the cortex and the corpus callosum were measured using the stimulated echo acquisition mode (STEAM) sequence with a motion probing gradient (MPG). The fast and slow components of the apparent diffusion coefficient (ADC) were obtained by fitting a biexponential attenuation function to the measured signals. The conductivity tensor of the tissue was calculated from the fast component of ADC and a fraction of the fast component. The mean conductivity (MC) of the cortex and the corpus callosum were 5.1 × 10^-2 S/m and 8.9 × 10^-2 S/m, respectively. Using a spin-echo imaging sequence, diffusion-weighted images were obtained with b factors up to 3600 s/mm². Conductivity tensor images were calculated from images of the fast component of ADC and images of the fast component fraction. Tissues with highly anisotropic cellular structures, such as the corpus callosum, the internal capsule, and the trigeminal nerve, exhibited high anisotropy in conductivity.

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