The operation of conventional electric motors is based on the electromagnetic interaction between the coil and permanent magnet, and the size of these parts limits the miniaturization of these motors. Nano-motors, which generate driving force, are indispensable for achieving future nano-machines. We propose a novel rotary motor whose operating principle is based on the gyromagnetic effect due to electron spin, and this is accomplished by spin-injection and spin-relaxation. This spin-transfer motor makes ultimate miniaturization possible thanks to its simple structure.

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A strong and sharp write-head magnetic field distribution is necessary in order to achieve higher density in perpendicular magnetic recording. The magnetic field of a head medium model was calculated by using a finite element method (FEM) simulator. In studying the head-medium interaction, an FEM simulator was combined with a magnetizing reversal model to realize self-consistent calculation. The magnetic circuit formed by a single-pole head and the soft-magnetic underlayer of a double-layered medium produces an efficiently strong magnetic field. By taking account of the head-medium interaction, a stronger and sharper head field distribution was produced.

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The recorded magnetization structures of longitudinal and perpendicular recording media were investigated by magnetic force microscopy in a temperature range between −50 and 300 °C. We found that when the sample temperatures are increased, variations in recorded magnetization occur preferentially in regions recorded with shorter bit lengths for longitudinal media. On the contrary, they tend to occur in regions recorded with longer bit lengths for perpendicular media. The behaviors of variations in magnetization structures with heating differ slightly bit by bit even for similar bit lengths.

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This paper discusses the possibility of iron loss reduction in non-oriented electrical steel (NO) sheets with a composition corresponding to JIS grade 35A210, and estimates the optimum iron loss from experimental data. The hysteresis loss of processed pure NO steel was decreased by 0.27 W/kg from the present 35A210 standard. The 0.35-mm-thick NO sheets with random {100} textures and the optimum crystalline sizes of polycrystals and withoutprecipitation may decrease iron losses from 2.0 W/kg to 1.0 W/kg, because random {100} textures may reduce theeffects of steel surfaces on iron losses and make coercive forces low, and optimum crystalline sizes minimize total iron losses. If pure NO sheets with random {100} textures are used in motors, the iron loss of a motor may become low, notonly because those of the core materials are low, but also because the motor core characteristics improve as a result of uniform flux distributions due to the low coercive force and lower internal stress caused by magnetostrictions. The decrease in the hysteresis loss was about 20%, relative to the present 35A250 standard, in a 12-pole 9-slot motorwhere a core made of pure NO was excited by a NdFeB bonded permanent magnet, although the decrease in thehysteresis loss of the core material was only about 18%.

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An experiment was carried out to investigate the effect of MnO substitution, mole ratio n { = Fe³⁺/(Co²⁺+Ni²⁺+Mn²⁺)}, reaction temperature, and concentration of alkali on the magnetic and physical properties of Co-Ni-Mn ferrite prepared by the chemical coprecipitation method without post-annealing. The chemical coprecipitation compositions were chosen according to the formula (CoO)_0.5(NiO)_0.5-x(MnO)_x·n/2(Fe₂O₃), where x varied between 0 and 0.5 and n varied between 1.80 and 2.00. To remove the superparamagnetic substance, the coprecipitation fine particles were etched with dilute sulfuric acid. As a result, in the (CoO)_0.5(NiO)_0.3(MnO)_0.2·1.95/2(Fe₂O₃) composition, when the reaction temperature and excess NaOH were 60°C and 0.5 mol, the following magnetic and physical properties were obtained: saturation magnetization σs = 79.77×10^-6 Wb·m/kg, residual magnetization σr = 47.38×10^-6 Wb·m/kg, coercivity H_cJ = 184 kA/m, and average particle size D = 19.61 nm.

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We newly prepared two types of DMS films deposited on quartz glass substrates by molecular beam epitaxy (MBE). The compositions of the DMS films are ZnMnTe and ZnMnSe. To determine the basic characteristics of these DMS films, we evaluated their transparency and Faraday rotation, and evaluated the ac magneto-optical properties at 1.6 kHz. Finally, we discussed the potential of these DMS films in the development of applications such as optical CT.

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To establish a technique for fabricating microstructural devices using half-metallic manganese oxideswithout any negative effect of microfabrication, we investigated the effects of defects in La_0.7Sr_0.3MnO₃ film caused byAr ion milling and a method for removing them by means of annealing. Our results show that Ar ion milling results ina resistance increase of up to several orders in magnitude with a damage depth of about 40 nm. We found that annealing in oxygen atmosphere corrects these problems almost completely. Furthermore, we actually fabricated model devices and demonstrated that undamaged devices can be fabricated by annealing in oxygen after the milling process.

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We fabricated Co₂MnSi/(Mg)/Al-O/CoFe MTJs using UHV magnetron sputtering. The interfacial chemical bond between Co₂MnSi and Al-O was intensively optimized by changing plasma oxidation time for Al-O and by inserting a Mg layer. The Mg inserted layer between Co₂MnSi and Al-O effectively suppressed the generation of interfacial magnetic impurities. Finally, we successfully observed a giant TMR ratio of 203% at 2 K in the MTJ with a 1.0 nm-Mg layer inserted. The spin-polarization for Co₂MnSi estimated from this TMR ratio was 0.97-1.00, which indicated that an almost perfect spin-polarized state was achieved. We also investigated the relationship between the TMR ratio and the site-ordering level of Co₂MnSi. As a result, we found that an L2₁-ordering state is not necessary to achieve high spin-polarization for Co₂MnSi in MTJs.

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Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a full-Heusler alloy Co₂Cr_0.6Fe_0.4Al (CCFA) thin film and a MgO tunnel barrier. Cross-sectional high-resolution transmission electron microscope observations clearly showed that all layers of CCFA/MgO/Co₅₀Fe₅₀ MTJ layer structures were grown epitaxially and were single-crystalline. The fully epitaxial CCFA/MgO/Co₅₀Fe₅₀ MTJs, where we used the difference in the coercive forces to form the antiparallel magnetization configurations between the lower and upper electrodes, demonstrated high tunnel magnetoresistance (TMR) ratios of 90% at room temperature (RT) and 240% at 4.2 K. This result suggested that a CCFA film composition close to the stoichiometric one is essential for obtaining high spin polarizations in CCFA thin films. The fully epitaxial CCFA/MgO/Co₅₀Fe₅₀ MTJs with exchange-biasing, where a Co₅₀Fe₅₀ upper electrode was used in a synthetic ferrimagnetic Co₅₀Fe₅₀/Ru/Co₉₀Fe₁₀ trilayer exchange-biased with an IrMn layer through the Co₉₀Fe₁₀/IrMn interface, exhibited high TMR ratios of 109% at RT and 317% at 4.2 K. From the obtained TMR ratio of 317% at 4.2 K, a high tunneling spin polarization of 0.88 at 4.2 K was estimated for epitaxial CCFA films with the B2 structure. These results confirm the promise of an epitaxial MTJ using a Co-based full-Heusler alloy as a key device structure for utilizing the potentially high spin polarization of this material system.

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For the development of room temperature spin-filtering devices with a ferromagnetic barrier, very thin ferromagnetic barrier films were required. Co-ferrite thin films are prepared by the surface plasma oxidization of a CoFe₂ underlayer deposited on MgO (001) single crystal substrates. During oxidization, the substrate temperature was varied from 523 K to 673 K. The plasma oxidized CoFe₂ films had a spinel structure, 4-fold symmetry in the plane, and an epitaxial relationship with the CoFe₂ underlayer. The lattice parameter of Co-ferrite thin film was 0.828 nm, which is 1.2% less than that of bulk. The interface between the CoFe₂ and its oxide was relatively smooth. When the substrate temperature during plasma oxidization was lower than 623 K, magnetization of CoFe₂ and Co-ferrite rotated independently. XPS and MOKE measurements identified that the hard and soft phases as Co-ferrite and CoFe₂, respectively. Measurements of the magnetic properties showed that the magnetization of the Co-ferrite thin films was about 1100 emu/cm³, which is 2.6 times more than that of bulk (420 emu/cm³). This phenomenon may be explained by the exchange of Co and Fe cation distribution in our Co-ferrite films.

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A new method of strain sensing using the stress-magnetoresistance (MR) effect was investigated. In thisstudy, an Ni₈₇Fe₁₃ (at.%) alloy film with in negative magnetostriction and a magnetive MR effect was used for strainsensing. The resistance increased with increasing compressive stress and decreased with increasing tensile stress. A gas pressure sensor was demonstrated using the film.

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We have developed a cryocooled superconducting magnet for the 28 T hybrid magnet. The liquidhelium-free hybrid magnet has been designed to generate the magnetic field of 28 T that can be accomplished bycombining 9 T generation due to the cryocooled superconducting magnet with 19 T generation due to a water-cooledresistive magnet, which is inserted into a room bore of the superconducting magnet. In this work, we developed the 10T cryocooled superconducting magnet with the 360 mm room bore, whose inner coils are wound for employinghigh-strength Nb₃Sn wires in consideration of large hoop stress. The liquid helium-free hybrid magnet has reachedthe generation of 27.5 T, which is greatly useful for high magnetic field science. The hybrid magnet also achieved thehigh magnetic-force field (B·dBz/dz) of 4500 T²/m, which could levitate materials of small magnetic susceptibility such as an InSb semiconductor.

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Micro magnetostrictive vibrator using Iron-Gallium alloy (Galfenol) was investigated. Galfenol is an iron-based magnetostrictive material with the magnetostriction more than 200 ppm, high permeability μr > 100 and Young's modulus of 70 GPa. The material is machinable to free of the shape by conventional cutting process, and sustainable for tensile, bending, and impact. Micro actuator using Galfenol equipped with iron yoke and winding coil, therefore, has advantages over PZT type, in simple, low voltage driving, high robustness and wide temperature operation range. This paper describes the performance of a micro vibrator improved to our previous prototype, in configuration, material, and fabrication process. The vibrator using stress-annealed Galfenol machined to the rod of 1mm diameter was observed the displacement of 1.2μm, high bandwidth of 30 kHz and high tensile robustnesswithstanding suspended weight of 500g. The vibrator was also verified useful as speaker which can generate clearsound from the power of a portable music player.

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We investigate a bending actuator based on unimorph, lamination of Galfenol (Iron-gallium alloy) and non-magnetic material. The Galfenol U-shape yoke bonded with stainless plates (lamination) is wound coils, and iscomposed close magnetic loop with connected an iron plate. The magnetostriction in longitude direction is constrained by the stainless, thus, the lamination yields bending deformation with the current induced. The advantage of the actuator is simple, compact and ease of assembling including winding coil, and high tolerance against bending, tensileand impact. We machined the yoke from a plate of 1mm thickness of Galfenol of Research grade using ultra highprecision cutting technique. The prototype with lamination thickness of 1mm was observed the displacement 13 μm and 1st resonance 1.6 kHz, and the high bending (tensile) tolerance withstanding suspended weight of 500g.

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Somatosensory evoked field (SEF) using a 39-channel SQUID system was carried out. We proposed a new method for improving the signal-to-noise (SN) ratio. The proposed method, combining a reference coil (hardware) withadaptive filter (ADF) processing (software), was applied to the SEF data. First, independent component analysis (ICA) was applied to the SEF data, and correlation coefficient between each independent component and measureddata with the reference coil was calculated. Second, the adaptive noise processing was applied to frequencycomponents obtain by the discrete wavelet transform (DWT). The SN ratio of averaged SEF data obtained by proposed method was improved than ordinary averaging method. We confirmed that the proposed method, combining information of the hardware (reference coil) and the software technique (the ICA and the ADF) is useful to improve the SN ratio of the SEF data.

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The energy source of the artificial heart is located outside body. Moreover, signal transmission system is important to control the implanted device and to monitor inside body environment. Transcutaneous power and signal transmission system is useful, because it doesn't penetrate through the skin. The signal transmission coil, which is called figure-eight coil, is set in power transmission coil. Induced voltage from power transmission in signal transmission coil can be canceled by this signal transmission coil, because the direction of figure-eight coil is opposite in each loop. We design signal transmission circuit by using PIC (Peripheral Interface Controller), so we examine character of signal transmission in power transmission system.

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Hyperthermia is a therapeutic method that necrotizes cancer tumora by heating. We developed an implantable heat element for tumors, which is excited by applying an external magnetic field. The previously proposed soft-heating method of hyperthermia features the use of thermosensitive ferrite as the heat element. This means that the heat element can control the temperature automatically by referring to the Curie temperature of the thermosensitive ferrite. The heat element consists of a thermosensitive ferrite and a metal ring. For wrapped around the ferrite to increase the heat quantity. For application to superficial tumors, the utility of a plane-type spiral coil was examined. As a result, it was confirmed that the influence of the magnetic gradient in excitation does not greatly influence the temperature characteristic. Moreover, arranging the magnetic ferrite in a plane-type coil is effective in easing the excitation current value and the directivity of the magnetic flux.

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