(Mn_0.24Zn_0.09Fe_0.67)Fe₂O₄ (MZF) thin films were grown on Si substrates without and with MOSFETs by pulsed laser deposition (PLD). The deposition of MZF films was carried out by the following two procedures: (1) “1-step deposition,” in which 300-nm-thick MZF film was deposited at 800°C, and (2) “2-step deposition,” in which 10-nm-thick MZF film was deposited at 800°C and 300-nm-thick MZF film was deposited at 27°C followed by post–deposition annealing at 800°C for 1 h under an O₂ pressure of 1.3 × 10^-3 Pa. For both preparation procedures, epitaxial growth of MZF thin film with (111)-orientation was observed. The saturation and remanent magnetization of MZF thin film depends on the preparation procedure, and the highest magnetization was obtained for film prepared by 1-step deposition. A microfabrication process in which preparation of MZF thin film was limited to the gate areas of Si-MOSFETs was attempted, using a combination of the abovementioned processes and etching processes: (1) 1-step deposition followed by wet chemical etching, and (2) 2-step deposition. In the 2–step deposition, a lift-off process was inserted before 27°C deposition. I_D-V_DS characteristics before and after magnetization of the MZF thin film was measured. As a result, modification of the drain current was observed. The modification was brought about by the Lorentz force, which was caused by the magnetic field induced by remanent magnetization. For MZF/Si-MOSFETs fabricated by 1-step deposition, the modification of the drain current was on the order of several μA when the gate voltage was 5 V. For MZF/Si-MOSFETs fabricated by 2–step deposition, the modification of the drain current was on the order of a few dozen pA when the gate voltage was 0.8 V. It was also clarified that the degree of modification increases with decreasing gate length. These results suggest that this principle could be used in a novel nonvolatile memory application.

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Mixtures of metallic Pauli paramagnetic MoO₂ and half-metallic ferromagnet CrO₂ were prepared by planetary ball milling. The magnetization M, resistivity ρ, and magneto-resistance ratio MRR were measured for (MoO₂)_x(CrO₂)_1-x from _x = 0 to 1. M and |MRR| rapidly decreased with increasing MoO₂ content. Rpm-dependence of the coercive force H_c was observed in the x = 0.05 sample.

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To use L1₀-FePt film with magnetic storage media, it is essential to reduce the thermal annealing temperature so that L1₀ phase can be obtained. By using Ar-discharge cleaning before sputter-deposition of FePt film, with the aim of removing residual gas impurities in a sputtering chamber, especially water vapor, we reduced the temperature at which FePt film begins to change from a disordered phase to an ordered one (L1₀ phase) to 290°C, and the temperature at which the transition is complete to 350°C. These temperatures are lower than the lowest values hitherto obtained by internal baking of a sputtering chamber using preheating of the substrate (with the same aim of removing residual gas impurities). This success will facilitate the practical use of L1₀-FePt film.

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A flexible disk medium composed of Co-Ni-Mn spinel ferrite fine particles was investigated in order to confirm its high-density recording performance. This medium was prepared from particles with a mean size of 25 nm using a spin coater without burnishing. The average surface roughness and particle size of the coated disk were approximately 20 and 34 nm, respectively. The recording characteristics were measured on a spinstand tester at a rotating speed of 2940 rpm, using a floating MIG head for writing and reading. The linear recording density at 50% of maximum output was 52 kBPI, whereas that of commercial zip media (Fe-Co particles) was 67 kBPI. The overwrite performance is very important for high-density recording, and it was better than 28 dB, which was close to the results for zip media at 1 MHz. The carrier-to-noise ratio for this disk was 32.2 dB after writing a 10 MHz signal, while the signal-to-noise ratio was 20.2 dB with the band width of 50 MHz, after writing a 20 MHz signal. The resuls of experiments showed that the Co-Ni-Mn spinel ferrite disk has potential for use in high-density data storage tapes.

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The magnetic duplication technique using patterned master media is a promising means of writing servo signals onto hard disks at high speed and low cost.It is expected that the direction of the applied magnetic field in the duplication process significantly influences the duplication characteristics.The objective of this paper is to clarify the influence of the oblique magnetic field out of the master plane.Experiments showed that the reproduced waveform from a slave duplicated with an oblique field is asymmetric near both edges of the protrusion of the master.The asymmetric waveform is improved by increasing the field, but the duplication characteristics with an oblique field are still inferior to those with an in-plane field.Computer simulation of the magnetization distribution of the slave duplicated with an oblique field shows that the distribution is asymmetric near both edges of the protrusion of the master, coinciding with the experimental results.

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We studied the thermal magnetic noise of TMR heads by using micromagnetic simulation, which considers an effective random thermal field corresponding to the thermal fluctuation. In this paper, we report the relationships between the thermal magnetic noise spectrum and the TMR head parameters. The free layer and the synthetic ferrimagnetic (SF)-pinned layer have individual magnetic resonant peak frequencies which depend on the internal magnetic fields, such as the permanent magnetic biasing field or the unidirectional exchange coupling field, between the pinned layer and the antiferromagnetic layer. The magnitude of the thermal magnetic noise increases with a decrease in either resonant peak frequency. Moreover, the magnetic resonant peak frequency depends on the TMR sensor aspect ratio, namely the ratio of width to height. Two peaks appear in the thermal magnetic noise spectrum if the individual resonant frequencies of the free and SF-pinned layers, which depend on the internal field strength, are markedly different.

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The magnetization distributions of recording layers recorded by magnetic head writing and magnetic duplication were calculated by the two-dimensional finite element method. The recording characteristics of the two methods were evaluated by comparing the magnetization distributions. In head recording, conspicuous bit shifts appeared when the recording current was optimal. In magnetic duplication, slight bit shifts were obtained when the strength of the applied field was greater than optimal. The reproduced output signals were calculated from the magnetization distributions of recording layers recorded by magnetic head writing and magnetic duplication. As a result, it was found that the output voltages of magnetic duplication were the same as those of head recording.

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A magnetic particle with a coercivity control layer (CCL), which stacks a hard magnetic region and a soft magnetic region, can create a lower coercivity than a conventional magnetic particle without a soft magnetic region. In this paper, the coercivity reduction mechanism is considered from the viewpoint of magnetic torque, and it is found that the exchange interaction between the hard region and the soft region assists the magnetic switching in the hard region, and that the magnetic torque due to magnetic anisotropy is decreased by the formation of a non-uniform magnetization configuration in the hard region. The thermal stability of a magnetic particle with a CCL is found to be less than that of a conventional magnetic particle with the same anisotropy constant but more than that of a conventional particle with the same coercivity. As a result, a thin-film medium that comprises magnetic particles with a CCL can be used as a recording medium without damaging the thermal stability. Moreover, it is found that incoherent magnetic reversal takes place at a finite temperature for a magnetic particle, even though its reversal mechanism is coherent at 0 K.

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The influence of the erased state of a recording medium on the read response of a GMR head was investigated using a micromagnetic simulator that takes into account the full interaction between a GMR head and a double-layered medium. The calculated results clearly showed that a baseline shift occurs for a dc-erased medium. In addition, the magnetization configurations in the shields and the soft underlayer (SUL) result in complicated roll-off properties: the amplitudes of the output signal was increased by suppressing the longitudinal bias field strength when the vortex magnetizations in the shield and SUL rotate counter-clockwise, and vice versa.

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Dot arrays with diameter D = 80-245 nm were made from Co₈₀Pt₂₀ (20 nm) films with a large perpendicular anisotropy energy. Coercivity increases as D decreases, and reaches 7.6 kOe at D = 80 nm. The switching volume for the dot arrays, estimated from the field sweep-rate dependence of the coercivity, was very small in comparison with the dot volume: about 7% of the dot volume when D = 140 nm, for instance. However, the angular dependence coercivity of these dots exibits a typical rotational type of magnetization reversal. Moreover, MFM images revealed that all the dots show a single domain state during the magnetization reversal. Comparison of the coercivity and the anisotropy field suggests that the reversal process starts from a nucleation at the center of the dot followed by a propagation process. This possibility was confirmed by numerical calculation. It was estimated that the switching field distribution, SFD, of dot arrays was mainly due to the distributions of the c-axis of the hcp-CoPt lattice and the dot diameter. Calculated results indicate that the magneto-static coupling between the dot arrays must be a dominant factor in determining the SFD value when the dots are used for patterned media with a recording density of ∼1 Tbits/inch².

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In perpendicular magnetic recording, reduction of nonlinear distortion is necessary in order to achieve a higher areal density as well as to improve the signal-to-noise ratio. CoPtCr-SiO₂ perpendicular magnetic recording media with various SiO₂ contents were used to examine nonlinear distortion mechanisms and optimization of pre-compensation was investigated by the 5^th harmonic method. The results showed that the nonlinear distortion was caused by nonlinear transition shift (NLTS) and nonlinear amplitude distortion caused by transition percolation. This was supported by micro-track model calculations. Therefore, the pre-compensation values should be optimized by taking both nonlinearities into account.

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Magnetic dot arrays were fabricated by using focused ion beam (FIB) lithography to pattern a continuous CoPt film with the aim of establishing design guidelines for patterned media with a soft magnetic underlayer. First, the magnetic influences of Ga ion irradiation were investigated in order to understand the characteristics of FIB milling. It was found that the implantation of Ga ions in the recording layer or the soft magnetic underlayer seriously affected the magnetic properties. Magnetic dot arrays were then fabricated, taking account of this effect. The switching field of the film drastically increased with the patterning and exhibited a further increase with decreasing dot size. The slope of the remanent magnetization curve decreased considerably as the dot spacing was decreased. The results suggest that patterned media should have a smaller dot size and larger spacing.

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Spike noise of double-layered perpendicular magnetic recording media with exchange-biased soft-magnetic underlayers (SULs) was studied on the basis of readback signals from a GMR head. By obtaining their averaged waveform and standard deviation, readback signals were classified into two groups: signals from the hard magnetic component and signals from the soft magnetic component. No spike was observed when the SUL retained a single domain condition: either (1) no magnetic field was applied, or (2) an external magnetic field less than the bias field was applied to the easy axis of the SUL. When an external magnetic field greater than the bias field was applied to the easy axis of the SUL, the domain wall caused spike noise with a width of a few micrometers. When an external magnetic field was applied to the hard axis of the SUL, single-peak pulses with a width of about 200 nm were observed. Since these pulses were distributed randomly in the media and the pulse density increased with increasing magnetic field, they probably originated from ripples in the SUL.

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The track-edge effect in perpendicular magnetic recording was investigated. Dc-erased tracks were used to clarify the characteristics of track-edge noise for various perpendicular media. The slope of the hysteresis loop at coercivity, (slope parameter, α), was used as a measure of the intergranular exchange coupling, and the magnetic cluster sizes were estimated by comparison with Voronoi cell calculations using auto-covariance functions. It was found that media with a large slope parameter showed large track-edge noise, and thus a clear positive correlation between track-edge noise and magnetic cluster size was observed. It is concluded that reduction of the magnetic cluster size is necessary not only for improvement of the transition jitter but also for reduction of track-edge noise.

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In order to investigate the pinning assist effect of Co_100-xFe_x-nano-oxide layer (NOL), the MR performance of Co_100-xFe_x-NOL specular spin-valves with a wide range of Fe contents was studied. Enhancement of both the MR ratio and the exchange bias field was comfirmed by increasing the Fe content in the Co_100-xFe_x-NOL. This might be due to the interdiffusion of Fe atoms from the nonequilibrium fcc Co_100-xFe_x layer with high Fe content. Furthermore, a ferrimagnetic component is considered to be formed in Fe-rich Co_100-xFe_x-NOL, which improves the degradation of the exchange bias field by the ferromagnetic coupling through the NOL.

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Since L1₀ ordered Fe-Pt has very high uniaxial magnetic anisotropy, it is an attractive candidate for ultra-high-density storage using heat-assisted magnetic recording. But its Curie temperature of 500 °C needs to be lowered if a temperature rise above the Curie temperature is to be achieved by the use of moderate laser power. Control of the Curie temperature was investigated in Fe_60-xNi_xPt₄₀ thin films sputtered on quartz glass substrates. L1₀ phase (001) texture was found in all the films with x = 0 to 24, indicating that the crystalline structure is L1₀ phase. XRD rocking curves revealed that the (001) orientation is much improved as x increases, while the order parameter S is gradually degraded, and magnetic anisotropy energy is decreased. A Curie temperature of around 300 °C, which may be suitable for heat-assisted magnetic recording, is obtained for x = 20 to 24.

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Suppression of spike noise and wide adjacent track erasure (WATE) are important technical issues for perpendicular recording media (PRM) with a soft magnetic underlayer (SUL). To solve these problems simultaneously, we propose in this paper a new type of SUL with negative uniaxial perpendicular magnetic anisotropy (Ku_⊥) induced by material with negative uniaxial magnetocrystalline anisotropy (K_u^grain). For the proposed SUL, it can be expected that (1) WATE will be suppressed due to a wide distribution of magnetic flux under the return yoke, and that (2) spike noise will be eliminated due to the formation of a Neel wall instead of a Bloch wall. We selected hcp-CoIr as a negative k_u^grain material and fabricated c-plane-oriented CoIr film by sputtering. K_u^grain of c-plane-oriented CoIr film had a minimum value of -6 × 10⁶ erg/cm³ (saturation magnetization, M_s = 920 emu/cm³ ) at an Ir content of 22 at.%. In PRM using c-plane-oriented CoIr films as SULs, WATE could be suppressed compared with the PRM using amorphous CoZrNb as SUL. And from evaluation of envelopes for PRM using c-plane-oriented CoIr films as SULs, it was found that spike noise could not be clearly observed with a CoIr thickness below the calculated critical thickness of Neel wall formation.

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An experiment was carried out to examine the effect of composition, heat treatment, and nitrogenation conditions on the magnetic properties of Sm-Fe-Co-Mn nitrides with TbCu₇-type structure. The optimum preparation conditions of the compounds were as follows: composition {Sm₁₀(Fe_0.9Co_0.1)_89.5Mn_0.5}₈₄N₁₆; roller velocity 50 m/s; heat treatment 700°C × 60 min in high-purity Ar gas; and nitrogenation condition 420°C × 15 h in high-purity N₂ gas. Typical magnetic properties of the obtained powders were as follows: J(_r = 0.96 T, H_cJ = 699.2 kA/m, (BH)_max = 138.3 kJ/m³ (17.4 MGOe), and T_c = 508°C. Recoil loops of the hysteresis curve and X-ray analysis showed that the sample was an exchange spring magnet. The value of (BH)_max of the bonded magnet prepared from {Sm₁₀(Fe_0.9Co_0.1)_89.5Mn_0.5}₈₄N₁₆powder was 92.1 kJ/m³ (11.6 MGOe) when the density of the bonded magnet was 6.05 Mg/m³. The magnetization process of these nitrides is of the pinning-type. The reversible temperature coefficient of J(SUB>r was α(J(SUB>r) = -0.04%/°C in the range from 25°C to 125°C.

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An experiment was carried out to examine the application of an Sr-Zn-W-type hexagonal ferrite bonded magnet as a hysteresis bonded magnet in a non-contact-type torque limiter using a magnet. The magnetic properties of Sr-Zn-W-type hexagonal powders ware first examined in order to prepare a bonded magnet. The preparation conditions for a typical sample were as follows: chemical analysis composition, Sr²⁺_0.93Zn²⁺_0.93Fe²⁺_1.02Fe³⁺_16.07O27; reaction sintering condition, 1300°C × 4.0 h in air; average particle size after pulverizing, 0.85 μm. The magnetic properties of Sr-Zn-W-type hexagonal ferrite powders are σ_s = 95.5 × 10^-6 Wb·m/kg, H_cJ = 60.5 kA/m. Next, an injection molding bonded as a hysteresis bonded magnet was prepared by using these powders and Sr-M-type ferrite powders. Non-contact-type torque limiters were made experimentally by using these bonded magnets. The torque value of a torque limiter prepared from an Sr-Zn-W-type ferrite bonded magnet was found to be better than that of a torque limiter prepared from an Sr-M-type ferrite bonded magnet, and the leakage magnetic flux decreased by 13%.

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Melt-spun ribbons of Didymium-Fe-Co-Nb-Y-B system alloys were prepared by the single-roller liquid rapid-quenching method. The effects of Y addition, wheel velocity, and heat treatment on the magnetic properties were investigated. The optimum preparation conditions of the compounds were as follows: composition Didymium_12.5Fe_69.8Co₁₀Nb₁Y_0.7B₆; wheel velocity 20.0 m/s; heat treatment 650°C for 10 min. Magnetic properties of this ribbon were (BH)_max = 126.4 kJ/m³ and HcJ = 1409.0 kA/m. The value of (BH)_max for the isotropic compression molding Didymium_12.5Fe_69.8Co₁₀Nb₁Y_0.7B₆ bonded magnet prepared by using the ribbons annealed at 650°C for 10 min was 66.3 kJ/m³ and the density was 6.1 Mg/m³. The irreversible loss of this bonded magnet was -3.58 % (at 150°C). It was found that the irreversible loss was improved by Y addition.

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An experiment was carried out to investigate the manufacturing condition for chemical coprecipitation method, and the effect of Li₂O₃ substitution on the magnetic and physical properties of Co-Ni spinel ferrite fine particles. As one of the examinations, alkaline aqueous solution inflowed into the metal mixture solution on a constant speed. As a result, this method yeilded fine particles with more stable properties than the pH control method (the conventional method). As regards the (CoO)_0.5(NiO)_0.5-x(Li₂O₃)_0.5x·Fe₂O₃ (x = 0—0.5) composition, the new method showed a good properties in (CoO)_0.5(NiO)_0.3(Li₂O₃)_0.1·Fe₂O₃ composition, with magnetic properties of σ_s = 64.3 x 10^-6 Wb·m/kg (51.2 emu/g), H_cJ = 406.0 kA/m (5.12 kOe). K₁ = 10.0 x 10⁴ J/m³, K₂ = -39.6 x 10⁴ J/m³. The average particle size was about 34 nm. The rotational hysteresis integral (Rh), which was related to the magnetization mechanism of these fine particles was 1.66, and it was found that the magnetization mechanism was an incoherent rotation one.

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Regularly aligned arrays (linear and honeycomb arrangements) of Y-shaped Ni₈₀Fe₂₀ (permalloy) nanodots buried in silicon wafers were fabricated using the damascene technique, and electron beam lithography (EB). The distributions of surface magnetization were observed by means of magnetic force microscopy (MFM), and the internal spin distributions were analyzed by a micromagnetic simulation using the Landau-Lifshitz-Gilbert equations (LLG eq.). Spin distributions are determined by the effects of geometric shapes and magnetostatic interactions working between adjacent dots.

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The magnetic properties of a low-Curie-temperature Mg₁₊₁Fe_2-2xTi_xO₄ system, which could be used in magnetic induction hyperthermia, were investigated. The thermo-magnetization curves and magnetic susceptibilities at high temperatures for water-quenched and slow-cooled Mg₁₊₁Fe_2-2xTi_xO₄ samples were measured. The Curie temperature decreased with increasing Ti concentration x and increasing cooling rate. Rietvelt analysis was performed to determine the site occupancy at A and B sites of the constituent atoms in the spinel structure. The exchange interactions, J_AB, J_AA ,and J_BB, were then estimated by molecular field theory. The calculated Curie temperatures as a function of x and those for samples with different heat treatments were in good agreement with experimental data. The effect of the inter-atomic angle φ between Fe-O-Fe on the Curie temperature was also investigaed under the super-exchange interaction regime. The reduction of the super-exchange interaction owing to the increase in angle φ contributes to decrease the Curie temperature.

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The paper describes the use of magnetoelastic ribbon in a remote temperature sensor. Magnetoelastic ribbon was placed in an ac magnetic field generated by an external coil. The vibration of the ribbon was monitored with a pickup coil and reached its maximum value at the mechanical resonant frequency, in accordance with the magnetostriction effect. We monitored the temperature by measuring the output voltage of a pickup coil at frequencies near the resonance. The maximum change in output voltage was 0.57%°C^-1, in the temperature range from 20°C to 80°C. This finding indicates the potential of the ribbon for use in a sensitive and compact remote temperature sensor.

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We previously reported that the electric permeability ε_r' of ferromagnetic nanocomposite oxide sputtered films with a Bi₂O₃-Fe₂O₃-PbTiO₃ ternary system is subject to change with an external magnetic field H and that electric polarization induced by a small ac magnetic field, ΔP_h(ω), is observed. To explain these experimental results, we proposed a model based on magnetization rotation of ferromagnetic nanoclusters dispersed in a dielectric matrix. However, it was found that, when Si-wafers are used as substrates, a depletion layer attributed to the MIS structure is formed in the film-to-Si interface, which seriously affects measurements of the magnetic-field-sensitive portion of the permeability Δε_r'(H). In order to eliminate this completely, we used heavily doped n⁺-Si wafers (ρ = 0.0016 Ωcm) as substrates, by which means we were able to obtain accurate Δε_r'(H)-value for a wide range of frequencies. In addition, we measured the temperature dependence of Δε_r'(H) and the saturation magnetization, 4πM_s, of a film to seek for the mechanism of this electromagnetic effect, as a result of which a close correlation was found to exist between Δε_r'(H) and 4πM_s.

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The characteristics of magnetic contact duplication for perpendicular magnetic recording media are investigated by using the three-dimensional finite element method. In order to magnetically duplicate a servo signal on perpendicular recording media, there are two methods of applying a duplication magnetic field. One is method to apply a magnetic field in a direction perpendicular to the disk plane (perpendicular field application, PFA), and the other is to apply a field in the disk plane (in-plane field application, IFA). In PFA, the dependence of the duplication performance on the field strength has an optimum value which is around the coercivity of the slave medium. In IFA, the duplication performance is improved by increasing the duplication field up to a certain field strength beyond which the strength the performance is saturated. Duplication characteristics of the slave media change a little even though the track width decreases in the case of PFA, while it decreases with decreasing track width in the case of IFA. The results of simulation show that IFA is more advantageous than PFA for duplication of perpendicular magnetic recording media.

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Double-barrier magnetic tunnel junctions (DMTJs) with an Fe(001) / MgO(001) / Fe(001) / MgO(001) / Fe(001) structure were deposited upon MgO(001) substrates by using molecular beam epitaxy. The DMTJs were found to show the TMR ratio of up to 110% and an extremely small bias voltage dependence (V_1/2 = 1.4 V under a positive bias application) at room temperature. We also investigated the middle-layer thickness dependence of the conductance curve in the DMTJs. Clear oscillations of the conductance were observed in a parallel magnetization configuration. This oscillation is thought to originate in the modulation of the tunneling conductance by the spin-polarized quantum well states created in the middle Fe layer.

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Magnetic tunnel transistors (MTTs) with double tunnel junctions were prepared in order to investigate the emitter voltage dependence of a magneto-current (MC). A three-terminal structure was fabricated, using metal shadow masks. It was observed that hot electrons contributed to a collector current. A transfer ratio of over 10^-3 was obtained in an MTT with double tunnel junctions. The MC decreased gradually with increasing emitter voltage. The emitter voltage at which the MC decreased to half its original value was over 1.5 V.

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We investigated spin-transfer switching (STS) in PtMn/Co₉₀Fe₁₀/Ru/Co₉₀Fe₁₀/Cu/Free (Free = Co₉₀Fe₁₀ and Co₆₀Fe₂₀B₂₀) current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) devices. Switching behavior was deeply related to the magnetization process of the free layers. Samples with Co₉₀Fe₁₀ free layers whose cell size was 80 nm ×180 nm showed sharp resistance switching due to STS. The average switching-current density (J_c) of the samples was in the range of 4.0×10⁷ A/cm² to 7.8×10⁷ A/cm². The dependence of J_c on the coercivity (H_c) was explained by thermally activated STS model.

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The stress that acts on the core by installing a stator in a frame influences the performance of a motor. To reflect this influence in the equipment design, the stress dependence of the magnetic property was examined for non-oriented electrical steels, which are the core materials. This time, the stress dependence of the magnetic power loss in the range of ±225 MPa was evaluated for high-grade non-oriented electrical steel sheets of 0.5 mm thickness, and the following results were obtained. (1) The influence on the magnetic power loss is larger under compression than under tensile stress. The loss increases rapidly with an increase in the compressive stress. However, when the stress exceeds -50 MPa, the saturation tendency of the loss gradually becomes strong. (2) The influence of the stress on the magnetic power loss is different in the rolling direction and the traverse direction. (3) A greater magnetic power loss that occurs with compressive stress is mainly due to an increase in hysteresis loss, and the eddy current loss also increases slightly. It is thought that this slight increase in the eddy current loss that occurs with compressive stress depends on the change in the anomalous loss.

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The authors demonstrated experimentally an influence of power supply noise on the magnetic field sensing of a high-frequency carrier-type magnetic field sensor. In magnetic sensing using such a magnetic sensor, an external ac magnetic field signal is modulated in amplitude in accordance with a high-frequency carrier signal. When a switching power supply is used for the carrier signal circuit, the power supply noise is also modulated in amplitude by the carrier signal. Therefore, both the upper and lower sideband spectra in the vicinity of the carrier signal are due not only to the magnetic field component but also to the power supply noise component. The sensitivity and frequency bandwidth of magnetic field sensing depend strongly on the noise level and noise frequency of the switching power supply.

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We previously developed quaternary diluted magnetic semiconductor (DMS; CdMnCoTe) films that exhibit a large Faraday rotation in the visible region at room temperature. We newly prepared four types of DMS films deposited on quartz glass substrates by molecular beam epitaxy (MBE). The compositions of the DMS films are CdMnTe, CdMnCoTe, ZnMnTe, and ZnMnCoTe. To determine the basic characteristics of these DMS films, we evaluated their transparency and Faraday rotation, and evaluated the ac magneto-optical properties of the DMS film (CdMnCoTe) at 500 Hz. Finally, we discussed the potential of these DMS films in the development of applications such as optical CT.

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This paper describes the time analog to digital converter (TAD), the TAD digital quadrature detection (TAD-DQD) technique, and their application to magnetic sensing. In-phase and quadrature components of an input signal are obtained by performing only addition and substitution operations on the data digitized by the TAD, using a sampling clock whose frequency is four times higher than the carrier frequency. Application of TAD-DQD to the position sensors using magnetoelastic waves in amorphous wires improves their resolution. TAD-DQD also simplifies the circuits of digital-output fluxgate sensors.

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We propose a new system for sensing the position of a wireless magnetic marker using phase detection. It consists of a resonating wireless magnetic marker, a driving coil, and pickup coils. A slim LC resonating marker (1.2 mm in diameter and 10 mm long) was fabricated and a deteactor was formed by connecting high-speed AD converters. The system has a position accuracy of around 1 mm, and it can be used for highly accurate position sensing without magnetic shielding, because it is free from earth field noise.

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Improvement of the sensitivity of a high-frequency carrier-type (HFC-type) magnetic field sensor through the use of an edge extension structure is reported. The HFC-type magnetic field sensor is composed of a rectangular CoNbZr thin film with a coplanar-structure Cu thin film as an electrode. The edge extension structure causes reduction of the sensor's demagnetization field effect. A variation in the sensor impedance was obtained as a function of the external magnetic field for edge extension lengths ranging from X= 0 mm to X = 1 mm. The length of the sensor was 1 mm, the thickness was 2 μm, and the widths were 20 and 80 μm. It was demonstrated that the gain of an HFC-type magnetic sensor with an edge extension length of X = 1 mm was three times higher than that of a sensor with an edge extension length of X= 0 mm. This result shows that an edge extension structure improves the sensitivity of an HFC-type magnetic field sensor.

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This paper describes a remote hydrogen sensor based on the mechanical resonance of a Pd-coated magnetic ribbon. The resonant frequency of the magnetic ribbon increases by 1.3% as the H₂ partial pressure is increased from 40 Pa to 8×10⁴ Pa. We demonstrate that this sensor can monitor a wide range of H₂ partial pressures wirelessly.

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A Current-induced magnetic field was detected by magnetic force microscopy (MFM) in order to evaluate a current flowing in a fine structure. Our system consists of a conventional magnetic force microscope and a feedback system for elimination of electrostatic force. As a first step in investigating the quantitativeness of this method, we observed the magnetic field around sub-micron-width gold wires where two currents joined with a third. First, we confirmed that the detected magnetic force signals qualitatively agreed with distribution of the magnetic field gradient around the sample. The amplitude of the magnetic force signal around the individual current paths was proportional to the current value. By taking account of the strength of the current-induced magnetic field, we theoretically estimated the amplitude ratio between the two different current paths. We then investigated the difference between the magnetic force signals observed around those current paths, and found that the experimental results quantitatively agreed with the theoretical values to some extent.

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We designed high-frequency-carrier type thin-film sensors to obtain high impedance change by controlling the annealing temperature, and investigated the relationships between the noise level, magnetic permeability, and domain structure. Meander-type sensor elements were fabricated, and a magnetic field resolution of 3.4 x 10^-8 Oe/Hz^1/2 at 501 kHz was obtained.

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2-D vector magnetic properties accurately represent the magnetic properties of various kinds of electrical steel sheets, because they can represent an alternating magnetic field in any direction and a rotating magnetic field by using the relationship between the flux density vector B and the field strength vector H. E&S modeling is proposed as a method for representing 2-D vector magnetic properties in magnetic field analyses. However, the E&S modeling used in magnetic field analyses is very time-consuming. To solve this problem, we propose complex E&S modeling on the assumption that both the flux density and field strength waveforms are sinusoidal. We carried out FEM analyses taking account of complex E&S modeling. Finally, we compared the analyses results considering complex E&S modeling with those of conventional E&S modeling, and made clear the efficiency of complex E&S modeling.

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Recently, many improvements in electrical machines have been achieved by replacing conventional permanent magnets with high-performance rare-earth magnets made from materials such as NdFeB. However, the distribution of residual magnetization in permanent magnets is usually non-uniform, and the residual magnetization cannot be measured directly. Thus far, predictions of residual magnetization in permanent magnets have only been possible by using cut-and-try methods. To overcome this difficulty, this paper investigates the establishment of a magnetization estimation method using numerical techniques. The results of simulated magnetization using the improved variable magnetization and Stoner Wohlfarth equation (VMSW) method are compared with actual measurements.

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This paper proposes a cable-less magnetic actuator that exhibits a very high thrusting force and is capable of being adapted to propel a robot within a pipe. The actuator contains a mechanical inverter that directly transforms dc from button batteries into ac. The mechanical dc-ac inverter incorporates a cantilever beam and a one-degree-of-freedom-model that switches under an electromagnetic force. A prototype actuator containing a mechanical dc-ac inverter was fabricated, and is able to move through a pipe of 14 mm inner diameter. Experimental results show that the actuator can move upwards at a speed of 26 mm/s. This cable-less actuator has many possible applications, including small pipe inspection and maintenance.

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This paper proposes a new cable-less of micro actuator that operates on the resonance energy of a one-degree-of-freedom model by using an electromagnetic force. The actuator is moved by the difference in inertia force during one period of vibration. A mechanical dc-ac inverter that transforms a dc power supply into an ac power supply was designed. The volume of the prototype cable-less of micro actuator with a dc-ac inverter was about 1 cm³. Experimental results show that the actuator can move at 4 mm/s in a vertical direction in a one dry cell model. Because the actuator can move only on magnetic substances, it has many possible applications for small pipe inspection, repair, biomedical uses, and machining.

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Magnetic gears used in a trial have superior performance characteristics. A magnetic spur gear meshes both internal and external gearing by exchanging the center distance. A magnetic bevel gear operates in the same way as a spur gear by exchanging the intersecting axle. A magnetic worm gear is constructed compactly in such a way that the worm is involved inside the space (torus) of a worm wheel. A magnetic skew gear is positioned at any center distance between the pinion and gear. Recently trial use has been made of magnetic planetary and diffential gears as accelerators for wind power generators. This paper describes the effect of the performance characteristics of correcting the whole depth which is composed of a permanent magnet. As a result, it is shown that the ordinary performance characteristics are maintained when the whole depth is reduced by one half.

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In a previous paper, we proposed a reluctance network analysis (RNA) model of a permanent magnet (PM) generator with a distributed winding and an overhang structure in which the permanent magnet is longer than the stator's stack in the axial direction. Using the RNA model, the basic characteristics of the PM generator were calculated accurately. A method for calculating the iron loss of the generator, however, was not discussed. In this paper, we estimate the iron loss on the basis of flux density waveforms calculated by using the RNA model. To verify the validity of the proposed method, the estimated values are compared with those given by a finite element method (FEM). In addition, we examine the accuracy of the flux and iron loss distribution obtained from the RNA model.

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Variable inductors can control the inductance of ac winding by dc excitation from a control circuit. For a large-capacity variable inductor, an EIE core is suitable because it is made of laminated iron and has no gaps for harmonic current reduction. EIE cores are expected to have practical applications to power control apparatuses in electric power systems. For optimum design of an EIE core, we previously proposed a reluctance network analysis (RNA). However, it is necessary to improve the accuracy of the iron loss calculation. This paper presents a method for modeling the eddy current caused by leakage flux in the laminated direction. We predict the paths of the eddy current, and express them in an electric circuit model. The eddy current circuit model is combined with the RNA model of an EIE core. We calculate the iron loss characteristics of the EIE core variable inductor, and evaluate the validity of the proposed method by comparing the calculated results with measured values.

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Recently, linear motors capable of transmitting motive power without the use of mechanical converters have been attracting attention as drive sources for transportation systems, and there have been practical implementations of linear induction motors and linear synchronous motors. The authors have been engaged in developing transportation applications of permanent magnet linear synchronous motors using high-energy magnetic materials. We have proposed a discontinuous armature LSM in witch the armature side is engaged only when accelerated/decelerated operation is necessary, instead of one in which thrust is constantly applied. However, an outlet edge certainly exists, because the armature uses a discontinuous arrangement method. This edge becomes a problem, because the cogging force that it exerts influences the controllability of the motor. This paper presents the results of an experimental examination and three-dimensional analysis of the cogging force exerted by the outlet edge. We deformed the shape of the armature to decrease the cogging force at the outlet edge, and the results are examined by using three-dimensional analysis.

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Recently, current suppression devices such as fault current limiters (FCLs) have been required to reduce excessive currents in power distribution lines when the short-circuits occur in the expanding electric power systems, which have high impedance in the fault condition and the low impedance in the normal condition. To realize the required operation, the dc magnetization point of magnetic fault current limiters must be designed to lie in the saturation region under normal conditions. Since a the magnetic FCL is characterized by a dc magnetization point, which depends on the shape of the magnetic core and the magnetic properties, numerical analysis was performed and experimental discussions were held to establish a design procedure for FCLs.

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In a previous paper, I presented a new sinusoidal-wave output inverter, which is based on the principle of magnetic oscillation. An ac voltage source is connected to an excitation winding of the magnetic circuit in series. Current flows 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. The inverter, therefore, can send electric power directly to the ac voltage source when the small signal-current is sinusoidal, and will be applicable to an electric power interconnection system. In this paper, I calculate the basic characteristics of the inverter in dc control to clarify the conditions for stable operation of the magnetic oscillation circuit by using SPICE. This paper describes the calculated results for the maximum output electric power of the inverter.

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This paper describes the effect of the solenoid dimensions in an electromagnetic launcher on the height of projection. The height of projection is calculated by combining the circuit equation and the equation of motion. The magnetic force is carried by the finite element method. The calculation errors of the height of projection are respectively 5.5%. In conditions where the charging voltage V = 68 V and capacity C = 3.66 mF (input power W = 8.46 J), the height of projection of a solenoid with an outer radius r_o = 19 mm and length l = 22 mm reaches a maximum.

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We studied the thrust force of a swimming-type magnetic micromachine. The micromachine was constructed from a permanent magnet and a spiral shape made of a tungsten wire. The magnet was magnetized in a diametrical direction. When a rotational magnetic field was applied, the machine rotated and moved in a fluid. It was experimentally found that the velocity of the micromachine trailing a wire was reduced when the kinematic viscosity was decreased. The shape of the micromachine that produced the largest thrust force was determined. To compare the analytical result with the experimental result, we made the micromachine by using a femtosecond laser. The analytical results agreed with the experimental results.

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