The effects of Ga-ion irradiation on a microstructure, layered structure, and magnetic properties of Co-Pd multilayers are investigated. A decrease of the diffraction peak in low angle X-ray diffraction showed that the regular interface between Co and Pd layers was blurred by ion irradiation. The ion irradiation changed the easy axis of magnetization from perpendicular to an in-plane direction at an ion dose of 5/spl times/10/sup 14/ and 5/spl times/10/sup 15/ ions/cm/sup 2/ for Co-Pd/sub 6/ and Co-Pd/sub 20/ multilayers, respectively. Magnetic force microscopy images of irradiated films showed that the magnetic contrast significantly decreased with increasing ion dose, which corresponds to a decrease of the perpendicular magnetic anisotropy.
The GMI effect has been studied in 3 different families of amorphous wires: conventional amorphous wires (125 μ m; m in diameter), cold drawn wires (50 and 20 μ m in diameter) and thin glass coated amorphous microwires (with metallic nucleus diameter of about 15 μ m) has been investigated in the frequency range 1 500 MHz.A remarkable difference in magnetic field dependence of the GMI effect can be attributed to the different magnetoelastic anisotropy of these three families of the wires.
We investigated both the read/write performance for sub-micron bits and the possibility of recording servo-patterns of over 300 Gbits/in2 by using patterned master contact duplication, which is expected to resolve the problems of conventional servo-track writing. The experimental value of the spacing loss factors forsub-micron bits resulting from the duplication was around 20 dB, which was lower than that for reportedcon ventional magnetic head recording. The reason for thelow value is that the duplication suffers less from recording demagnetization because a static recording method is used and the S* value of the slave is high. A reading experiment involving duplication using a master disk with a track width of 190 nm and a bit length of 123nm yielded a signal-to-noise ratio of 17.9 dB, which was a little larger than that of magnetic head recording. The simulation of a magnetic field to duplicate a high-density servo-pattern indicated that the magnetic field was large enough to record servo-patterns of as much as 370 Gbits/in2. These studies demonstrated the potential of this method for high-density servo-pattern recording.
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 (= Tmin), 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.
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.
Eddy-current testing (ECT) has been widely applied in manufacturing to the inspection of defects inside conducting materials. It, however, is still difficult to obtain accurate depth information on deep cracks and to detect cracks on the reverse sides of thick structures by using the technique. We conducted a theoretical analysis based on 3-D solutions of Maxwell equations to determine the optimum exciting frequencies and suitable positions of a sensor for both depth detection and reverse-side detection. An ECT probe consisting of a single-direction exciting coil with a spin-valve-type giant magnetoresistive (SV-GMR) sensor was employed in experimental inspection of 12-mm-and 22-mm-thick stainless steel (SUS) plates with 67% deep and 77% deep cracks, respectively. The experimental results show good agreement with our theoretical analysis. Thus it is confirmed that both the ECT probe and the theoretical analysis proposed in this paper are capable of detecting defects in a thick SUS plate.
We carried out a three-dimensional vector measurement of a somatosensory evoked field (SEF) with an electric stimulus to the right thumb, using three-dimensional second-order gradiometers connected to 39-channel SQUIDs, which can detect magnetic components perpendicular to the scalp (Br) and tangential to the scalp (BΘ, Bφ) simultaneously. A dynamic singular value decomposition method, with a time window and shift time, was applied to spatio-temporal magnetic data. First, averaging of the SEF data with a dynamic SVD was done with each trigger for stimulation. Second, dynamic SVD was applied to SEF data, having two frequencies ranges (1-80 Hz and 15-80 Hz), and with a time window of 10 ms and which was shifted every 1 ms in analysis. Two dominant singular values were obtained for the contralateral magnetic component in 90 to 110ms. Source localization of SI and SII activity with a ECD method showed dominant GOF (goodness of fitness) around 90ms. We concluded that the proposed dynamic SVD method, with a time window and shift time, is useful for reducing noise component in SEF data and discriminating multiple sources overlapping in time.
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.
Four kinds of Fe3O4/Ag granular systems were prepared from sintered mixtures of Fe3O4 and Ag or Ag2O. Magneto-resistances (MRs) 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 χc-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.
In this study, we present a method for fabricating magnetic dots array through nanosphere lithography and reactive-ion etching.Through this technique, one can control the magnetic dot size by tuning the etchingtime of nanospheres.As a demonstration, [Co(3A)/Pt(10A)] 15 films and dots were fabricated on Al2O3(0001) with Pt(111) buffer layers at 100•Ž.The measurement of polar magneto-optical Kerr effect showed a perpendicular magnetic anisotropy in both cases and a low squareness in Co/Pt nanodots system.The investigation of magnetic force microscopy showed that Co/Pt nanodots displayed a single domain behavior.
A magnetic probe containing a Hall sensor and pickup coil was developed, and its accuracy was confirmed by comparison with standard ring sample results under zero stress. The magnetic minor hysteresis loops of a lowcarbon steel plate sample were measured by using this probe under uniaxial tensile stresses. It was found that both the coercivity Hc and hysteresis loss WF can be measured accurately by means of a magnetic probe. In the perfectly elastic region, from 0 to 90 MPa, Hc and WF decrease with increasing external stresses due to domain re-orientation, and they start to increase a little in the micro-plastic range. In the plastic stage, Hc and WF increase almost linearly with external stresses as a result of dislocation pinning effects. This clear relationship between magnetic properties and external stresses is also valid for NDE applications.
" Proximity effects" could be the superior mechanism responsible for lowering the quality factor (Q) of ferromagnetic spiral inductors, apart from ferromagnetic resonance considerations. In this paper, a model extraction from previous measurements is described. In particular, the extracted series resistance Rs is discussed with regards to skin depth and current crowding contributions in the metal traces. Comparing air-core and ferromagnetic spirals, it is shown that" proximity effects" are enhanced with magnetic materials leading to a much stiffer increase in Rs with frequency (f2 instead of √ f). This points out Q being naturally always lowered at the same frequency with ferromagnetic spirals, even if an adequate high FMR is realized. Thus, it is necessary to reconsider the design of spirals when using magnetic materials and some solutions are suggested at the end of this paper.
The temperature-dependent electrical resistivity of antiferromagnetic Cr1-χVχ alloys (χ≤0.04) was measured under hydrostatic pressures up to 3 GPa. It was found that the Neeel temperature TN decreases approximately linearly and the residual resistivity ρ0 increases with increasing χ, reaching a maximum near χ=0.035. The pressure dependence of TN is strongly dependent onχ. For Cr (χ=0), TN decreases with increasing pressure, but the rate of decrease becomes sluggish above approximately 2 GPa. The value of TN for χ=0.015 decreases almost linearly up to 3 GPa. On the other hand, the value of TN for χ=0.035 reaches zero at 0.7 GPa. These results are discussed in relation to the quantum phase transition.
Previously we revealed that spin-sprayed ferrite films are usable for GHz-range noise suppressors. For actual use, the films must retain excellent characteristics after the reflow soldering process. In this study, we investigated how changing the compositions of films influences their electric resistivity and the noise suppression effects obtained after annealing at 260° C. We plated 3-μm-thick ferrite films #1 (Ni0.2Zn0.1Fe2.7O4) and #2 (Ni0.4Zn0.3Fe2.3O4) onto polyimide sheets. The resistivity of film #1 decreased markedly, from 4 × 102 Ω cm to 1 × 100 Ω cm as a result of the annealing. On the other hand, film #2 exhibited a smaller decrease, from 6 × 104Ω cmto2 × 104 Ω cm. The reflection parameter S11 and transmission loss Δ Ploss measured on a microstrip line for film #1, especially below 1 GHz, were increased by the annealing. This is unfavourable for use of film #1 in lowpass filters that are required to absorb noises only in the GHz range. On the other hand, S11and Δ Ploss for film #2 were not significantly affected by the annealing. This film exhibited Δ Ploss of 40 ‰ at 10GHz.Moreover, the value of S11for the film below 10 GHz was sufficiently weak, less than -12dB.Thus, we succeeded in fabricating aGHz-rangenoise suppressor, with excellent heat resistance.
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 proposed previously by authors for designing the SR motor, and evaluated the optimum exciting phase. Furthermore, we improved the proposed method so that the basic characteristics 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.
Impedance measurements as a function of the applied magnetic field are performed at high frequency using an experimental set-up specially adapted for planar samples, which is based on a microstrip transmission line. Microwave measurement techniques and a consistent data reduction procedure allow obtaining very detailed and accurate impedance measurements. The results for two different samples, an amorphous ribbon and a trilayer thin film, reveal the importance of the ferromagnetic resonance contribution at high frequency. Besides, fine details of the magneto-impedance behavior at low field confirm that it is mainly governed by magnetization processes. At high frequency, when the ferromagnetic resonance contribution at low field weakens, an impedance peak re-appears, that seems to be related with the usual peak that exists at low frequency.
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.
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.
Present study reports on magnetostatic interactions in highly-ordered arrays of Ni nanowires embedded in nanoporous alumina membranes. We use two techniques supplying complementary information: ferromagnetic resonance, FMR, studies from which we derive information of the whole array of nanowires, and magnetic force microscopy, MFM, that informs us about the magnetic state of individual nanowires. From FMR study of the angular dependence of resonance field and itsline-width it is concluded that the magnetostatic interaction plays an important role to decrease the effective anisotropy field of individual nanowires. This is confirmed by analysis of MFM images at remanence and its comparison with vibrating sample magnetometer measurements.
