This paper describes a variable inductor and its application to a power controller for use in an electric power system. First, we present an orthogonal-core-type variable inductor and a three-phase 6.6 kV-100 kVA reactive power compensator using orthogonal cores. In addition, applications to power apparatuses such as a series compensator and a phase shifter are described. Next, we introduce a novel EIE-core-type variable inductor designed for a larger capacity. The operating characteristics of a trial 6.6 kV-300 kVA reactive power compensator are presented. Finally, we present a method of calculating the operating characteristics of the variable inductors based on a method of three-dimensional nonlinear reluctance network analysis (RNA) proposed by the authors.

View full abstract

Recording simulations were used to determine the factors which influence the recorded track width in perpendicular media. Reducing the width of the main pole and adding side shields to the head are effective methods to write narrower tracks, whilst trailing shields can increase the SNR. Exchange coupling in the recording layer increases the track width, but erase bands are narrowed. However, the magnetisation of a pre-recorded track can influence the switching of grains at the edges of adjacent tracks if the exchange coupling strength is large.

View full abstract

Thermal stability of written bits with different linear densities on [MgO/FePt] _n/MgO 4-nm/SiO₂ 4-nm/Fe-Ta-C 200-nm/Glass perpendicular media with two different multilayer structures has been investigated by Magnetic Force Microscope (MFM) equipped with an in-situ heating system capable up to about 200°C. For Disk with n =2 (Disk A), only a few reversed domains appear in the center area of 10 kfci bits at 200°C, which is due to the strong demagnetization field at this linear density, while higher density bits have no observable degradation even at 200°C indicating good thermal stability of this disk. On the other hand, for Disk with n = 3 (Disk B), much more reversed domains are observed inside the 10 kfci bits at 200°C. The observed MFM signal decay is correlated with the temperature dependent magnetic properties.

View full abstract

Magnetic and crystallographic properties of barium ferrite (BaM) thin films, deposited onto Pt, Pd, and Pd-Pt underlayer at the different substrate temperature (T_s) of 400 to 600°C have been studied. The thickness of underlayer is about 20 nm and the thickness of barium ferrite film is 30 nm. From x-ray diffraction patterns, all of the BaM films grown on the three kinds of underlayer show its c-axis orientation perpendicular to the films plane. It is found that the coercivity values in perpendicular direction (Hc_perp) of the BaM/Pd-Pt films are higher than those of the BaM films deposited on Pd and Pt underlayer. Substrate temperature Ts for crystallization of BaM was reduced from 600°C to 450°C. The Hc_perpof 2.1 kOe for BaM (30nm)/Pd-Pt (20nm) film can be achieved with c-axis orientation. Pd-Pt underlayer not only improve the value of c-axis dispersion angle Δθ₅₀ and perpendicular coercivity Hc_perpbut also effective to reduce grain size of BaM thin film.

View full abstract

We studied the magnetic properties of TbFeCo thin film sputtered onto TiN underlayer with different surface morphologies resulted from different thicknesses. According to the results of atomic force microscopy, the surface roughness of TiN film is increased as the film thickness increased. Initially the coercivity is increased sharply from about 2 kOe to 6 kOe for an increase of underlayer thickness to 60 nm then the increasing rate of coercivity becomes very slow. At about threefold increase in the coercivity is thought to be due to the enhancement of domain wall pinning effects caused by an increase of surface roughness in the TiN underlayer. For the underlayer thickness of more than 60 nm, the M-H loop has been changed from rectangular to nonrectangular resulting remanent squareness ratio of less than unity. There is no significant effect of TiN underlayer thickness on the saturation magnetization has been observed.

View full abstract

Four kinds of Fe₃O₄/Ag granular systems were prepared from sintered mixtures of Fe₃O₄ and Ag or Ag₂O. Magneto-resistances (MR_s) were measured at room temperature for samples with Ag volume fraction x between 0 and 0.4. Samples including relatively large Fe₃O₄ grains showed -1% to -1.4% room temperature MR ratios (MRR) at 1 T. On the other hand, samples including Fe3O4 nano-particles showed large negative room temperature MRR of about -4% to -5% at 1 T near the percolation threshold of χ_c-0.2. It was suggested that Fe₃O₄/Ag/Fe₃O₄ paths were effective for the large IMRRI by the elastic conduction of spin-polarized electrons between Fe₃O₄ nano-particles. Possibility of spin accumulation in small Ag particles was also shown for this system.

View full abstract

The temperature dependence of the electrical resistivity was measured for face-centered cubic (fcc) Fe₇₀Ni₃₀ Invar alloy under high pressure between 2 and 8 GPa. It was found that the electrical resistivity below 6 GPa shows a minimum at a low temperature around 10 K (= T_min), which decreases with increasing pressure and disappears at 8 GPa. At 8 GPa, the electrical resistivity is proportional to T² below 30 K, which indicates the Fermi liquid property. The resistance minimum is caused by a new high-pressure magnetic phase such as a RSG phase. These results show the pressure-induced magnetic phase transition from the ferromagnetic phase to the RSG phase below 6 GPa and a crossover from the RSG phase to Fermi liquid around 8 GPa.

View full abstract

The temperature-dependent electrical resistivity of antiferromagnetic Cr_1-χV_χ alloys (χ≤0.04) was measured under hydrostatic pressures up to 3 GPa. It was found that the Neeel temperature T_N decreases approximately linearly and the residual resistivity ρ₀ increases with increasing χ, reaching a maximum near χ=0.035. The pressure dependence of T_N is strongly dependent onχ. For Cr (χ=0), T_N decreases with increasing pressure, but the rate of decrease becomes sluggish above approximately 2 GPa. The value of T_N for χ=0.015 decreases almost linearly up to 3 GPa. On the other hand, the value of T_N for χ=0.035 reaches zero at 0.7 GPa. These results are discussed in relation to the quantum phase transition.

View full abstract

FePt/FeMn bilayers were deposited onto MgO (100) substrates by ion beam sputtering system. The dependence of in-plane and out-of-plane exchange bias fields (H_E) and coercive fields (H_C) on the thicknesses of both ferromagnetic (FM) and antiferromagnetic (AF) layers has been investigated. The out-of-plane exchange bias field is half of the value of the in-plane exchange bias field, which is may be due to the dispersion of anisotropy of FePt layer or may be because of the alignment of the spins of FeMn layer. The FM thickness dependence of in-plane and out-of-plane exchange bias is similar; however, the AF thickness dependence of out-of-plane exchange bias is different from that of the in-plane case.

View full abstract

Submicron-sized Co particles were fabricated by patterning single-crystal Co thin films, and their magnetic domain structures were observed by magnetic force microscopy (MFM). The Co films (250 nm in thickness) were epitaxially deposited onto Al₂O₃ (001) single-crystal substrates by electron beam evaporation, and from thesefilms (with their c-axis parallel to the surface normal) circular dots with diameters of 0.5, 1, and 2.5 1μm were patterned by electron beam lithography and Ar ion beam etching. All the dots fabricated proved to suffer from side wall etching, resulting in cone shapes in the case of 0.5μ and 1μm diameters. In dots with diameters of 1 and 2.5μm, maze patterns in domain structure were clearlμEobserved, whereas concentric contrast became dominant in 0.5μm dots. Numerical simulation based on the Landau-Lifshitz-Gilbert equation revealed that these dotspossess components of both perpendicular and vortexmagnetization simultaneously.

View full abstract

Inspection of bare printed circuit boards (PCBs) consists of evaluating not only imperfections in the PCB conductor but also PCB conductor dimensions and alignment. An eddy-current testing (ECT) probe consisting of a spin-valve giant magneto-resistance (SV-GMR) device was used as a magnetic sensor, with a planar meander coil as an exciter, and applied to PCB conductor dimension and alignment inspection. High-frequency (18MHz) excitation was used to inspect a PCB conductor, with thickness of less than 10μm, and a high-resolutionscan pitch of 20 μm enabled the examination of high-density PCBs. The characteristics and configuration of the proposed ECT probe are presented in this paper. Inspection examples of a high-density PCB with a 100 μm PCB conductor width and gap verify that the proposed ECT probe yields accurate results.

View full abstract

A permanent magnet repulsive-type magnetic bearing balance system was designed and fabricated in our lab. It is used for measuring micro-masses where the function of mass measurement was confirmed by transferring the additional mass to the control current of a voice coilmotor (VCM) device installed at one side of the balancebeam. Some of the measurement characteristics of the system, such as linearity, sensitivity, and hysteresis were measured experimentally; in addition, the accuracy of measurement was evaluated. This paper describes how thevoice coil motor was modulated to achieve better measurement characteristics, such as lower hysteresis and higher accuracy. Theoretical aspects of the system, including simulation of the modulated VCM model, are explained, and the experimental results confirming the improvement of the system characteristics are reported.

View full abstract

We proposed a new method for decreasing transformer effect from excitation current to sense coil in an orthogonal fluxgate operated in the fundamental mode. The point of this method is to use a U-shaped magnetic wire core on each branch of which two identical sense coils are wound and to arrange the two coils in counter series. As a result, induced voltage is reduced by a factor of 1/3 from that observed with a single wire core. The levels of the magnetic noise and drift are reduced substantially. For example, the noise level at 10 Hz decreased from 0.5 n T/√Hz to 0.08 n T/√Hz for small excitation current 4.1 m A with 5.8 m A dc bias. The driftof the sensors is confined within the range 0.5 n T for the U-shaped F G and 1 n T for the single core F G.

View full abstract

We calculated the eddy current distribution in an aluminum plate, excited perpendicularly by a small ring coil for quantitative understanding of the interaction of the eddy currents with a flaw in the plate. The calculation is based on the equations developed by Dodd and Deeds for axis-symmetric problems. After confirming the accuracy of the calculated results by comparing them with the measured data, we characterized the profiles of amplitudeand phase of eddy currents in the aluminum plate. We confirmed that the phase of the eddy currents depends linearly on the distance between the source point and the observation point, as found in an ideal one- dimensionalcase, when the angle between the vertical line and the line connecting the source point to the observation point is less than 60 degrees. We extended the equation to express the magnetic field that may be produced out of the aluminumplate by the interaction between injected eddy currents and a small flaw in the sample. On the basis of theequation, we also show how to evaluate the magnetic fieldfrom a flaw.

View full abstract

We developed a new micro-fabricated cantilever with a spin-valve sensor (MR cantilever) for a scanning magentoresistance microscope (SMRM). Since thespin-valve sensor has a self-biasing mechanism, it allowsthe SMRM to respond to an observed magnetic field linearly without any external bias magnetic field, and itmakes the SMRM more sensitive to magnetic fields. Wehave succeeded in introducing the self-biasing mechanism into the SMRM system by fabricating the spin-valve sensor on a cantilever.

View full abstract

In this paper, we design and analyze an outer-rotor-type multipolar switched reluctance (SR) motor, and examine the possibility of realizing an electric vehicle (EV) with an SR motor inside each of its two rear wheels, that is, an EV with a gear-less and in-wheel layout. We used a method for calculating the operating characteristics proposedpreviously by authors for designing the SR motor, andevaluated the optimum exciting phase. Furthermore, we improved the proposed method so that the basiccharacteristics of the EV with SR motors can be calculated, and we investigated the initial and steady-state currents and the maximum speed of the vehicle.

View full abstract