After mixing RuO₂ and CrO₂ powders, (RuO₂)_x (CrO₂)_1-x was sintered at a low temperature of 473 K. The effects of using an RuO₂ spacer between CrO₂ grains were systematically studied for values of x between 0 and 1. The x-dependence of the averaged saturation magnetic moment μ _s per transition metal ion abruptly decreased even at x = 0.03, and it linearly varied in the range 0.3 ≤ x ≤ 1, where the estimated magnetic moment per Cr ion was 1.43 μ _B, a 30% reduction from the value of 2 μ _B for pure CrO₂. The magneto-resistance ratio (MRR) remained almost unchanged in the range 0 ≤ x ≤ 0.7.

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The high-frequency permeability of Mn₈₀Ir₂₀ (at.%)/Fe₈₉Si₁₁ (at.%) exchange-coupled films for microwave applications was evaluated. For this purpose, a micromagnetic simulator based on the LLG equation was introduced. When the complex permeability of exchange-coupled and non-exchange-coupled films with the same Fe-Si thickness of 100 nm was compared in the experimental results, parameter Δf_r/f_r of the exchange-biased Fe-Si film was larger than that of a single Fe-Si film with uniaxial magnetic anisotropy. This is where f_r is the ferromagnetic resonance (FMR) frequency and Δf_r is the frequency bandwidth of the FMR half line-width, i.e., where Δf_r/f_r corresponds to the inverse of the FMR Q factor. An exchange-stiffness dispersion model was introduced into the LLG simulation to investigate the behavior of FMR in the exchange-biased film. We found that the exchange-stiffness dispersion in Fe-Si gives rise to a distribution of exchange bias in the thickness direction, and that such spatial distribution increases parameter Δf_r/f_r. The authors consider that the exchange-stiffness in polycrystalline Fe-Si film is not constant and has a Gaussian distribution, because distributed exchange-stiffness occurs with lattice defects and/or grain boundaries. When average stiffness constant A was 1.7 μerg/cm and its standard deviation σ_A was 0.83 μerg/cm, the calculated results agreed with those from experiments.

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Cancellation performance of a loop-current array shielding module depends on the overcompensation method used to adjust current in the loops. In previous experiments we used a single value as an overcompensation factor to all of the loops in the array. In this paper a new method of the overcompensation is proposed and verified numerically. In this method overcompensation factors are calculated independently for each of the loop-current. Simulation results show almost two times improvement in the attenuation ratio and 6-8 times expanding of the best cancellation area by the new method. An example of the implementation of the proposed overcompensation method is described in the paper.

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The optimization of head field gradient and inter-granular exchange coupling was studied usinmicromagnetics simulation so that we could predict future R/W properties with combinations of different head and medium properties in perpendicular magnetic recording. The results revealed that SNR degradation with media exchange coupling could be suppressed by using a shielded head with a high field gradient. Shielded heads are also effective when the average size of media grains is reduced to 75% to achieve SNR improvements of 2-3 dB.

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The duplication characteristics of perpendicular magnetic media were analyzed by using metal evaporated (ME) tape as a slave medium. In the case of bit printing (BP), the best duplication characteristic was obtained at a duplication field of 4 kOe, about 2 times higher than the coercivity of the ME tape. On the other hand, in the case of edge printing (EP), duplication characteristics were saturated when the duplication field was more than 3kOe. When the duplication field was strengthened, in the case of BP, the peak position shifted towards the outside of the magnetic layer of the master, whereas, in EP, the peak position shifted towards the center of the magnetic layer. The calculated MFM output waveform obtained by using computer simulation almost coincided with the experimental result, and the cause of the sub-peak could thus be explained. It was concluded that EP has better duplication characteristics than BP.

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We demonstrated the micromagnetic simulation of magnetic duplication for perpendicular magnetic recording (PMR) media. The magnetization distributions of the PMR media duplicated by edge printing (EP) and bit printing (BP) were investigated. The dependence of duplication characteristics on the duplication field was also estimated. An AC erase state in the off-track region appeared for a strong duplication field in EP. The dependence of the duplication characteristics on the duplication field we found in this study is in agreement with that calculated by macroscopic-magnetization analysis in a previous report. Although the intergrain exchange constant has almost not influence on the duplication characteristics in EP, the duplication characteristics in BP are improved as the intergrain exchange constant increases.

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The magnetic properties and recording performance of hard/soft-stacked media consisting of a magnetically hard layer (9-10 nm) underneath a very thin soft layer (2 nm) with a large saturation magnetization were investigated. Magnetic energy calculations revealed that reducing the strength of the interfacial exchange coupling between the hard and soft layers reduces the remanence coercivity, H_r. Moreover, an increase in the saturation magnetization of the soft layer <M_s^soft> significantly enhances the H_r reduction. It is theoretically predicted that the grain volume of hard (10 nm)/soft (2 nm) stacked media having <M_s^soft> of 1000 emu/cm³ could be reduced to about 1/3 that of conventional media whilst maintaining good recording writability and thermal stability. An experimental study of stacked media revealed that the magnetization reversal mechanism changed systematically as a function of the strength of the interfacial exchange coupling, as predicted theoretically. The H_r reduction on adjusting the interfacial coupling reached 22% of that of media consisting of directly coupled hard/soft grains. It was successfully demonstrated that hard/soft-stacked media having thin soft layers with a large <M_s^soft> showed better recording writability without degradation of SN_mR, recording resolution, or thermal stability.

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Gd-Fe-Co and SiN_x were prepared by magnetron sputtering using Ar or Kr gas. The sample structure consisted of glass substrate/underlayer SiN_x/Gd-Fe-Co/protective layer SiN_x. When the SiN_x layers were prepared using Kr gas, the coercivity H_c of Gd-Fe-Co increased. On the other hand, when the Gd-Fe-Co layer was prepared using Kr gas, the perpendicular magnetic anisotropy K_u and H_c of Gd-Fe-Co increased. The ratio of M_sH_c to 2K_u was also increased by Kr sputtering. This means that H_c increased at a greater rate than K_u. By etching the surface of the underlayer SiN_x prior to the deposition of the Gd-Fe-Co layer, it is possible to reduce H_c without affecting K_u. By combining the Kr gas sputtering and the etching, K_u can be increased without increasing H_c. A Gd-Fe-Co layer with a periodic structure of Gd and Fe-Co has larger K_u and H_c than alloys of Gd and Fe-Co. Etching the surface of the underlayer SiN_x is also effective for reducing the H_c value of the periodic structure of Gd-Fe-Co.

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The magnetization mechanism of an Nd-Fe-B HDDR magnet was studied by measuring its recoil curves. When compared with those of isotropic Nd-Fe-B sintered, HDDR, and melt-spun magnets, the behavior of the recoil curves of the HDDR magnet was similar to that of the recoil curves of the melt-spun magnet. This means that the isotropic HDDR magnet behaved like single-domain particles. In addition, calculated isotropic recoil curve that assumes only rotation of the magnetization of single-domain particles showed the same tendency as the recoil curves of the HDDR magnet. This result indicates that the recoil curves of an isotropic HDDR magnet were dominated by rotation of the magnetization, and were not significantly influenced by domain wall movement. Moreover, the recoil curve of an anisotropic HDDR magnet behaved similarly to calculated anisotropic recoil curve based on the rotation of the magnetization of single-domain particles with an orientation distribution. This means that the recoil curves of an anisotropic HDDR magnet were also dominated by rotation of the magnetization. These results suggest that the HDDR magnet behaved like single-domain particles in its recoil curves, which were dominated by rotation of the magnetization and were not significantly influenced by domain wall movement.

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With high quality thin films of the double perovskite Sr₂CrReO₆, we have investigated an electronic state of the surface of the Sr₂CrReO₆ thin film and the interface of bi-layer Sr₂CrReO₆ / MgO or SrTiO₃ film by X-ray photoemission spectroscopy (XPS). The Re 4f spectrum of Sr₂CrReO₆ has shown a multiple peak structure, which originates from the inherent electronic state of Re in half-metallic Sr₂CrReO₆. Moreover, it has been found that the electronic state in Sr₂CrReO₆ is preserved at the Sr₂CrReO₆ / MgO interface.

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This paper describes detailed studies of the easy axis alignment of L1₀-FePt nanoparticles synthesized by the recently developed “SiO₂-nanoreactor” method (Appl. Phys. Lett. 87 032503 (2005)). The L1₀-FePt nanoparticles can be made dispersible in styrene solution containing small amounts of oleic acid and oleyl amine. The hysteresis loop of the L1₀-FePt nanoparticles solution showed superparamagnetic-like behavior at room temperature due to the free motions of nanoparticles, indicating that the easy axis of the dispersed nanoparticles can be aligned by an application of external magnetic field. The easy axis of the L1₀-FePt nanoparticles was aligned and fixed parallel to the direction of the external magnetic field by performing free radical polymerization of styrene at 60 °C under an external field of 50 kOe. Powder X-ray diffraction measurements revealed that the L1₀-FePt nanoparticles/polystyrene composite thus obtained has a (001) preferred orientation showing a strongly enhanced (001) superlattice peak and a (002) fundamental peak, as well as a (003) superlattice peak. The composite showed strongly anisotropic magnetic properties with the room temperature coercivities perpendicular and parallel to the aligning field direction of 3.3 and 25 kOe, respectively. The anisotropy field of the composite was determined to be about 70 kOe at room temperature.

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Free layer structures, where two soft magnetic layers were ferromagnetically coupled with a synthetic antiferromagnet (SAF) through non-magnetic layers, were demonstrated to freely control the spin-flop field ( H_flop) and the saturation field ( H_s) of 0.32-μm-wide magnetic tunnel junctions in toggle magnetoresistive random access memories (MRAMs). In the free layer, by reducing the coupling strength through the non-magnetic layers, the magnetization reversal of each soft magnetic layer induced a spin flop of the SAF at a lower field (called the “induced spin-flop mode” ), resulting in an H_flop reduction. The H_swas significantly increased while maintaining a low H_flop by replacing the bilayer SAF with a multilayer SAF. The free layers using the induced spin-flop mode are expected to reduce the write field of toggle MRAMs with densities greater than 4 Mb to less than 50 Oe.

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We investigated magnetic damping parameters (α) in Co-Fe-B alloy thin films having various compositions, thicknesses, and annealing temperatures. Ferromagnetic resonance (FMR) was used to determine α values. The out-of-plane angular dependencies of the resonance field and the line width of FMR spectra were measured and analyzed by using the Landau-Lifshitz-Gilbert equation, taking the effect of magnetic inhomogeneities in the films into consideration. The Co-Fe-B films with an fcc structure phase had a larger α value than that of the film with a bcc structure. The damping parameter of the Co-Fe-B film was increased by increasing the B concentration and annealing temperature, and the very thin Co-Fe-B film (∼2 nm) had a large damping parameter. We discuss the advantages of Co-Fe-B thin film as a material for current-induced magnetization switching (CIMS) systems.

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This paper describes the use of a self-oscillator made by employing a magnetoelastic ribbon resonator as a remote viscosity and density sensor. The magnetoelastic ribbon was placed between a drive coil and a pickup coil. The vibration of the magnetoelastic ribbon was detected as an induced voltage by the pickup coil. The induced voltage was amplified (with an amplifier) and fed back to the drive coil, whose magnetic field increased the amplitude of the ribbon vibration. As a result, a self-oscillator was realized when a one-wavelength longitudinal elastic standing wave was excited on the ribbon. We demonstrated that the inverse of Q of the self-oscillator was proportional to the square root of the product of the viscosity and density of the surrounding liquids. These results suggest that this self-oscillator is a promising candidate for use as a compact remote viscosity and/or density sensor.

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A giant magnetoimpedance sensor with a step-like impedance property was obtained in the case of amorphous Co₈₅Nb₁₂Zr₃ soft magnetic thin film in a rectangle shape with an in-plane uniaxial easy axis in a direction nearly 60 degrees relative to the width direction of the element. It was shown experimentally that the magnetic field in which the step-like impedance change occurs has an almost constant value with a standard deviation in the microtesra (μT) range. The magnetic field in which the step-like change occurs includes information on the external magnetic field. To realize a magnetic field sensor with an accuracy of nT/Hz^1/2 by using this step-like phenomenon, a differential circuit was studied in combination with an alternating bias field in the kilohertz (kHz) frequency range. The aim of the differential circuit was to make the driving circuit into a digital logic circuit, by using pulse signals timed to coincide with the step-like changes. The alternating bias field increases the sampling number, because of the step-like changes in the bias frequency. The aim of the ac bias is to improve the sensor accuracy by using an averaging effect. This paper reports a first trial of the method. As a result, a high-linearity sensor without hysteresis was obtained, which had a linearity error of less than 0.5% in the range of ±100 μT. A measurement accuracy of 460 nT was achieved with a 20 Hz time constant of the output low pass filter (LPF).

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Magnetic force microscopy (MFM) has been applied to permalloy multistep-semicircular wires containing nearly-free magnetic domain walls (DWs). In this study, we investigated the effect of stray-magnetic fields from the probes in the MFM measurement using low-, medium-, and high-moment probes, which are coated by 12 nm-, 24 nm-, and 72 nm-thick CoPtCr films, respectively. By using the low-moment probe, the DW signal was clearly observed at the side of the wires, which is consistent with a micromagnetic simulation. By using the high and medium moment probes, in contrast, we observed complete and incomplete DW manipulations, respectively. These manipulation signals were found to be maximized immediately above the wire. These phenomena were analyzed by calculating the stray fields from the MFM probes. We also discussed the possibility of the controllable DW manipulation in terms of the stray fields and the MFM scanning sequences.

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We tried to control the magnetic anisotropy of a high-frequency carrier-type magnetic field sensor by varying the shape of the magnetic film instead of the induced anisotropy. We confirmed that the impedance of the sensor was changed by applying a magnetic field, and showed that the properties of the sensor could be controlled through the design of the magnetic film’ s shape.

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In a previous paper, I proposed a new sinusoidal-wave output inverter based on the principle of a magnetic oscillation circuit that has a dual dc voltage supply. An ac voltage source is connected to an excitation winding of the magnetic circuit in series. The inverter can supply electric power to the ac voltage source because the current flowing through the ac voltage source can be controlled by small signal-current flows through a control winding of the magnetic circuit according to the law of equal ampere-turns. This inverter could be used in an electric power interconnection system. In this paper, I present an improved sinusoidal-wave output inverter that can operate with a single dc voltage supply. The fundamental characteristics of the inverter are described in this paper.

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The Preisach model is constructed with some experimental loops that are measured to turn over at any external magnetic field to oppsite maximum one. It is possible to predict relations between magnetization and magnetic field, using the distribution function made from the experimental loops. It can think that the magnitude of distribution function imply the number of magnetic dipole in the magnetics. Therefore, it can expected that all values in the distribution function are positive. However, in the actual distibution function maken from the experimental loops, both areas having positive and having negative exist actually. In this paper, examples of adverse effects because of the large negative regions are shown. Then the moving model is applied as a solution of the problem. Predicted minor loops with the model are good agreement with experimental ones, confirming the effectivity of moving factor decided experimentally.

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An EIE core can be used as a variable inductor with a simple structure and good controllability. It is suitable for larger-capacity machines since it is with a laminated iron core. In addition, it has no gaps for harmonic current reduction. Therefore, it is expected that the EIE core variable inductor will be used as an automatic voltage regulator (AVR) for electric power systems. However, some aspects of the core operation have not been clarified. One of them is the main winding configuration. The EIE core has two main windings, which are wound around the top and bottom center-legs and connected so that the fluxes generated by the winding currents are in opposite directions. On the other hand, if the main windings are connected so that the fluxes are not in opposite directions, the control characteristic becomes worse, although the core structure remains the same. In this paper, the influence of the main winding configuration is investigated by using reluctance network analysis (RNA) and the finite element method (FEM).

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We studied a new type of three-phase induction motor excited by a single-phase power supply, and have succeeded in generating a three-phase rotating magnetic field in the stator of the motor. However, sufficient values for the output power and efficiency have not yet been obtained. This paper discusses the relationships between the stability of parametric oscillation and the magnetic flux density inside the outer magnetic path in the motor with a view to improving the output power of the motor. As a result, the condition of magnetic flux density distribution necessary for stable parametric oscillation is obtained.

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To meet the changing needs of society, battery-free portable equipment is required. This paper reports the results of a study that investigated the construction of a generator in a pen. The goal of this research was to produce light in an LED over a long period by using less vibrational energy. A linear generator that produces electric energy from vibrational energy was examined. As a result of examining the coil dimensions of the linear generator, we found that it obtained 40% of the energy for our goal. In addition, we confirmed that 58.6% of the goal could be achieved when the number of coils was optimized, and when a pipe made of magnetic material was adopted.

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The switched reluctance (SR) generator has various desirable features, including simple and solid structure, ease of maintenance, small moment of rotor inertia, and low cost, because it has no rotor windings and no permanent magnet. The solid structure would be advantageous for an ultra-high-speed generator such as a micro gas turbine generator, which the simple structure and small moment of inertia would suit a low-speed multipolar generator for use in wind turbine generators. However, the SR generator has not been put to practical use because an optimum design for the SR generator has not been established. In this paper, we present some considerations on the design of an SR generator and report an application for a variable-speed small wind turbine generator. We analyze the fundamental characteristics of the SR generator, conduct a quantitative analysis of the exciting circuit, and examine aspects of its variable-speed operation.

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Reduction of the iron loss and copper loss of induction motors has been thoroughly studied in a conventional sense. However, the fact that no method for estimating the harmonic loss due to the materials or dimensions of a motor has yet been established, has been an obstacle to harmonic loss reduction. We proposed an evaluation index E_w² for the harmonic loss that is caused by slots of a capacitor motor, which is a kind of a single-phase induction motor. E_w² is calculated from effective value of electromotive force with a virtual coil of the rotor surface. On no load, we found that E_w² was effective as an evaluation index for the harmonic loss. In this paper, we calculate E_w² on load and examine the propriety of using E_w² as a harmonic loss evaluation index.

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The purpose of this study was to clarify what effect electromagnetic fields had on living bodies. We experimented on Xenopus laevis as an individual. We compared the lengths of tails of frogs exposed to the electromagnetic field (20 kHz) of an IH cooker and a Merritt coil to the tail lengths of sham-exposure frogs. We experimented by changing the exposure time and strength of the electromagnetic field. The results for the present study revealed that an increase in the total daily exposure of Xenopus laevis to an electromagnetic field will speed up metamorphosis.

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Magnetic separation is an important method of purifying of cells or DNA. A properly designed magnetic separator causes less physical and chemical damage to a target and has a high separation rate. This paper presents a new high-throughput continuous magnetic separator for biomaterials labeled by magnetic beads. The separator consists of three rectangular coils, two circular coils, and a separation chamber. These instruments were designed by a numerically analyzing of the magnetic field and the movement of magnetic beads. A separation rate over 90% was obtained with this system in a separation test using magnetic beads.

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Magnetoencephalography (MEG) was recorded to detect the 40 Hz component in auditory steady-state responses (ASSRs) to stimuli (optimized chirp sounds) regularly repeated 40 times/s. The phase of 40 Hz component in ASSRs was synchronized to the repeated chirps. To obtain information on its mechanism, we used a differential-equation model for phase synchronization of ASSRs. The differential equation was numerically solved by the Runge-Kutta Method to obtain simulated results. The behavior of phase coherence of 40 Hz component in ASSRs obtained from the experimental results was compared with that shown by the simulated results and the simulated result predicted its experimental result to a satisfactory degree. In addition, the parameter representing the external force by stimulus in the model was found to be significantly influenced by the stimulus intensity. These results suggest that the model is validity.

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Simulations of finite-difference diffusion are used for solving the diffusion equation of nuclear magnetization in discrete space and time. The purpose of this study was to obtain the time step, Δt, and the spatial step, Δx, which minimize discrete errors in simulation. We evaluated the difference between a discrete solution and an exact solution that had been derived from the magnetization diffusion equation. The results revealed the existence of Δx, which minimizes discrete error. Spatial step Δx and discrete errors increased as time step Δt increased. The results should be useful for efficiently carrying out diffusion simulations within given time limitations for computation.

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Mechanical strain in biological tissues causes a change in the diffusion properties of water molecules. This paper proposes a method of estimating mechanical strain in biological tissues using diffusion magnetic resonance imaging (MRI). Measurements were carried out on uncompressed and compressed chicken skeletal muscles. A theoretical model of the diffusion of water molecules in muscle fibers was derived based on Tanner’s equation. Diameter of the muscle fibers was estimated by fitting the model equation to the measured signals. Changes in the mean diffusivity (MD), the fractional anisotropy (FA), and diameter of the muscle fiber did not have any statistical significance. The intracellular diffusion coefficient (D_int) was changed by mechanical strain (p<.05). This method has potential applications in the quantitative evaluation of strain in biological tissues, a though it poses several technical challenges.

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Hyperthermia is a method of treating cancer that uses heat to destroy tumors. Soft heating has been proposed as one method of treating hyperthermia. This is where the thermosensitive ferrite inserted into the tumor as a heating element produces heat in a high-frequency magnetic field. Although the heater needs to be implanted the heater in the tumor tissue, there are various advantages to soft heating, such as easy retreatment, localized heating of the tumor, and a low degree of invasiveness. We applied soft heating in this study. We created a complex heater composed of thermosensitive ferrite wound on a metallic ring. It produced a greater amount of heat due to losses through hysteresis and inductive current than thermosensitive ferrite alone. We could also control the temperature of the heater by using the Curie-point. To use this technique, it is necessary to miniaturize the element and achieve optimal performance. We demonstrated that the proposed heater has superior performance and operation at high power.

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Using stents is one method of treating stenosis of lumens from various causes. Cylindrical metallic stents are composed of alloy wire. After stents are implanted, however, stenosis may recur due to tumors or abscesses. It is particularly difficult to remove tumors or abscesses of the bile duct by surgery, because this is in a deep portion of the abdomen. We propose a non-invasive method of remedying tumors and abscesses by using thermotherapy with magnetically excited metallic stents. Clinical stents are not currently manufactured to allow for heating. We fabricated stents of thermosensitive magnetic material so they could be heated the heat controlled by external magnetic excitation for thermotherapeutic applications. We used a solenoid coil for clinical applications.

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We measured somatosensory evoked fields (SEFs) by electric stimulus to the right finger (thumb, fourth, and little finger) using a 39-channel SQUID system. In order to investigate relationship between phase lag and stimulus repetition frequency (SRF), delay time of a component synchronous the SRFs (2.0 to 30.3Hz) was calculated by the convolution of the reference signal and the measured SEF waveform. The phase lag was linear to SRF for at least three different ranges of the SRFs in each SEF data. It was tested for significance of the linear regression slope (β≠0, P<0.05). We also carried out souce estimation with these calculated slopes. Finally, in order to discuss relationship between phase-lag and SRFs, we demonstrated the simulation with the result of the phase lag characteristic.

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