Lattice constants and crystal structure of tetragonal Kondo compound CeAu₂Si₂ have been investigated at high pressure in order to examine pressure-induced change of crystal structure and gradual valence change of Ce atom. It is found that the lattice constants a and c decrease with increasing pressure without any discontinuity up to 13 GPa at room temperature. The bulk modulus B₀ and its pressure derivative B₀' were obtained to be 112 GPa and 3.2. These values are comparable with other Kondo compounds. From the ρ(T) curve at high pressure which does not change so much under high pressure, it is suggested that the valence of Ce changes sluggishly with pressure and the Kondo state of CeAu₂Si₂ is very stable at high pressure.

抄録全体を表示

We measured the resistivities of the heavy fermion SDW Ce(Ru_1-xRh_x)₂Si₂ (0.05 ≤ x ≤ 0.33) in a magnetic field up to 4 T. The resistivities of Ce(Ru_1-xRh_x)₂Si₂ (0.05 ≤ x ≤ 0.33) showed hump-type anomalies at T_N, indicating a gap opening on the Fermi surface due to the Fermi surface nesting. T_Ns shift to a lower temperature and disappear with incresing magnetic field. We evaluated the ratio of the gapped part σ_2p/σ_p on the Fermi surface and the gap parameter Δ/k_B T_N of the SDW to be 0.47 and 1.1 for Ce(Ru_1-xRh_x)₂Si₂ (x = 0.15), respectively. They are almost independent of the magnetic field, however they decrease as x deviate from 0.15.

抄録全体を表示

The comparison between the dual gradient recording method (DGRM) and the thermal gradient recording method (TGRM) for thermally assisted magnetic recording (TAR) were investigated using the Landau-Lifshitz-Gilbert equation, which adds a stochastic thermal field to an effective field. The magnetization patterns and read/write characteristics were discussed. It was clarified that the write performance of DGRM was superior to TGRM for achieving a high areal recording density.

抄録全体を表示

A simple design for the orthogonal fluxgate (OFG) mechanism in the fundamental mode is presented with detailed descriptions of the circuit. To avoid complexity in the circuit, an offset common to the fundamental mode is largely suppressed by using a U-shaped wire core and using a large dc bias current at the cost of increased power consumption. The remaining offset can be nulled at the final stage by a simple subtraction. The circuit presented in this paper consists of a logic inverter gate IC for a sinusoidal oscillator, two operational amplifiers, and a modulator/demodulator IC (AD630), as well as a U-shaped sensor head made of thin magnetic wire or thin magnetic ribbon. A magnetometer we developed with this design provided resolution of 10 pT/ √Hz for frequencies greater than 1 Hz.

抄録全体を表示

Permeability tensors μ_ij (i, j = x and y) of three different samples were evaluated by a proposed method. The method utilizes rotation of a sensing coil with a sample to induce off-diagonal components. The resultant tensors showed individual characteristics, especially in off-diagonal components. Discussion shows that the properties can be consistently related to each magnetization state by simple models. The method in this paper can be expected to provide not only a permeability tensor but also a picture of magnetization state in a simple manner.

抄録全体を表示

This paper describes a wireless hydrogen sensor that employs the resonance frequency change of PdNi-coated magnetic ribbons. A Pd_0.9522Ni_0.0478-coated magnetic ribbon exhibits a monotonous increase in resonance frequency with increases in hydrogen concentration. Because Pd absorbs hydrogen selectively and expands, the magnetic anisotropy in the ribbon changes from transversal single axis to isotropic in-plane. This weakens the ΔE effect and thus increases the resonance frequency. Consequently, PdNi-coated magnetic ribbon is confirmed as a sensitive wireless hydrogen sensor device.

抄録全体を表示

To reduce the iron losses of reactors under inverter power supply, the loss was calculated by using magnetic field analysis, which models a laminated core by combining a 3D solid-core model with a 1D steel plate model, using the finite element method (FEM). In this method, the structure of the laminations and the eddy currents in the steel plates can be taken into account. However, for reactors driven by inverter power supply, the calculated iron losses are much smaller than the measured results, because the anomalous eddy current loss induced by domain wall motion in the steel plates is neglected in the loss calculation. Therefore, this paper investigates a simple numeric modelling method that takes account of the anomalous eddy current loss by modifying the conductivity of the steel plates. First, the method is verified by comparing the calculated iron loss of one sheet of steel plate with the measured data. The method is then applied to the loss calculation of reactors under inverter power supply. The differences between the calculated and measured results become smaller when the anomalous eddy current loss in the steel plates is taken into account.

抄録全体を表示

An X-ray powder diffraction system in high temperature and in high magnetic fields was developed, which was performed at temperature ranging from room temperature to 473 K in the magnetic fields up to 5 T. The temperature stability was within ±1 K for 8 hours. To examine the ability of the system, high field and high temperature X-ray diffraction measurements were carried out for a novel ferromagnetic shape alloy, Ni₄₀Co₁₀Mn₃₄Al₁₆. We observed a field-induced reverse transformation in the alloy.

抄録全体を表示

A perpendicular anisotropy master medium (PAMM) is proposed. The PAMM is composed of CoPt film with perpendicular magnetic anisotropy and large saturation magnetization. The magnetization distributions of PAMM and conventional master media (using an FeCo soft magnetic layer) were analyzed by using micromagnetic simulation. It was found that the peak-to-valley value of the recording field and the recording field gradient at the edge of the patterned magnetic film of PAMM were larger than those of the conventional master medium. Furthermore, the peak-to-valley value of the recording field and the recording field gradient of PAMM did not depend on the strength of the printing field. The printing characteristic of PAMM is twice that of the conventional master medium. Furthermore, the optimum printing field for PAMM is 1 kOe lower than that of the conventional master medium. As a result, PAMM is expected to improve the printing characteristic of the bit printing method.

抄録全体を表示

The influence of the inclination angle of the master pattern on the edge printing characteristics for writing phase servo patterns on perpendicular magnetic recording media was investigated. Even if the master pattern angle is 40 degrees, the printing characteristics are only 10 percent lower than when the angle is 0 degrees. The influence of the inclination angle of the master pattern on the printing characteristics is also small when the bit length is changed. The contribution of the in-plane component of the recording field to magnetization reversal is large in edge printing. Although the perpendicular component of the recording field decreases markedly as the inclination angle of the master pattern increases, edge printing can be used for writing phase servo patterns on slave media.

抄録全体を表示

We studied what effect exchange bias had on magnetic noise under high-temperature or low-aspect-ratio conditions. We found that a steep increase in magnetic noise started at around 150°C with a low exchange bias (J_k∼0.4 erg/cm²), and attributed this to the decrease in exchange bias. We measured the dependence of magnetic noise with a high exchange bias (J_k∼1.0 erg/cm²) on temperature and found that magnetic noise was reduced under high-temperature conditions (∼250°C). We also found that magnetic noise could be diminished at room temperature even for a TMR head with a low aspect ratio (∼0.5). This indicates that the pinned layer instability increased by reducing the head size was improved with a high exchange bias.

抄録全体を表示

The stress in a read head in a hard disk drive was investigated by using finite element method (FEM) calculations. We compared the structurally induced effect of stress in a current-in-plane (CIP) structure and in a current-perpendicular-to-plane (CPP) structure. We found that electrodes in the CIP structure produced a large amount of in-plane anisotropic stress at the pinned layer. However, anisotropic stress induced in the CPP structure by the sensor-side material such as hard bias was less than that in the CIP structure. This was because the CPP structure did not have thick electrodes on the sensor side.

抄録全体を表示

Li-Zn-Cu ferrite polycrystal as a high-frequency ferrite is distinguished by its temperature sensitivity. In a previous paper, we pointed out that Li-ferrite, the main component of Li-Zn-Cu ferrite causes the temperature sensitivity. This result would suggest the influence of the large temperature coefficient of the anisotropy constant of Li-ferrite. The purpose of the present work is to investigate the effect of partial Mn substitution of Fe on the temperature sensitivity of Li-Zn-Cu ferrite polycrystal. While the permeability and the saturation magnetization at room temperature were reduced with greater Mn substitution, their temperature dependences were enhanced. It was clarified that the stronger temperature dependence of the apparent anisotropy field arose from partial Mn substitution and thereby intensified the temperature-dependent magnetic properties.

抄録全体を表示

FeCo thin films were prepared on MgO(100), MgO(110), and MgO(111) single-crystal substrates by UHV-MBE. The effects of substrate orientation and substrate temperature on the film growth structure and the magnetic properties were investigated. FeCo thin films with (100)_bcc, (211)_bcc, and (110)_bcc planes parallel to the substrate surface grew epitaxially on respective MgO substrates. FeCo(100)_bcc single-crystal films were obtained on MgO(100) substrates. FeCo(211)_bcc bi-crystalline films grew epitaxially on MgO(110) substrates with two types of domains whose orientations were rotated around the film normal by 180 degrees with respect to each other. FeCo(110)_bcc thin films grew epitaxially on MgO(111) substrates with two type variants namely, the Nishiyama-Wasserman and Kurdjumov-Sachs relationships. Atomically sharp boundaries were recognized between the FeCo thin films and the MgO substrates, where misfit dislocations were introduced in the FeCo thin films, presumably to decrease the lattice misfits. A 0.3% reduction of the lattice spacing normal to the substrate surface was observed for an FeCo thin film prepared at a substrate temperature of 100 °C. The lattice spacing reduction decreased with increasing substrate temperature. The magnetic properties of FeCo thin films grown on MgO substrates were influenced by the magnetocrystalline anisotropy and the shape anisotropy caused by the roughness of FeCo islands which form the FeCo thin films.

抄録全体を表示

Fine-particle composites consisting of high-permeability particles with a large size difference exhibit enhanced initial permeability. From an analysis of the initial permeability of a composite that includes Fe (1 micron) particles as a main component, we found that the microscopic demagnetizing field imposed on the particles is appreciably reduced, allowing enhancement of the initial permeability up to the intrinsic permeability of Fe particles. The significance of this effect is exemplified using composites that include Ni₅₀Fe₅₀ (6 microns) and amorphous Fe-Si-B-Cr (3 microns) particles. According to a calculation of the eddy current in spheres with high permeability, reduction of the particle size to less than 1 micron is essential for further improvement of the high-frequency performance of particle composites.

抄録全体を表示

We investigated the magnetic properties of Co₂MnSn Heusler alloy films, which were grown by alternate deposition of monoatomic Co, sub-atomic Mn, and sub-atomic Sn layers with electron-beam evaporation, by means of SQUID magnetometory and ¹¹⁹Sn Mössbauer spectroscopy. The Mössbauer spectra sensitively showed that the local magnetism at the Sn sites in the Co₂MnSn films depends on the substrate temperature. We also measured the tunnel magnetoresistance of the magnetic tunnel junctions with a Co₂MnSn/MgO/Co₂MnSn structure. The magnetoresistance of the junction where the magnetic circumstances at the Sn sites are relatively uniform is measured to be 2 % at 5 K at the present stage.

抄録全体を表示

We investigate and discuss electronic structures and tunneling conductance of magnetic tunnel junctions (MTJs) with the Co₂CrGa and MgO on the basis of the density-functional first-principles calculations. We found that the CrGa-terminated Co₂CrGa/MgO(001) junction has no interface states and preserves the high spin-polarization of Co₂CrGa at the interface. We showed that the large enhancement of the interfacial Cr spin moment plays an important role to make the half-metallic gap in the CrGa-terminated Co₂CrGa/MgO(001) interface. Finally, we have proposed that addition of an ultrathin Co₂CrGa layer between Co₂MnSi electrode and MgO barrier is effective to eliminate interface states in both sides of the junction with preserving the coherent tunneling through the Δ₁ channel of the MTJ in parallel magnetization.

抄録全体を表示

The Contactless Power Station (CLPS) is a cordless power supply system that makes use of electromagnetic induction generated by means of coils. We propose a desktop design for CLPS, using spiral coils, because it is convenient to be able to charge the batteries of a digital still camera, a cellular phone, and a PC on single desk. The primary coil are arranged so that the coupling factor becomes 0, since it is inconvenient for the primary coils to be excited by each other. However, when the primary coils are synchronized and driven, the magnetic flux interferes with the electric power transmission. Attention was paid to changing each phase on the primary coils. As a result, when the phase was moved, stabilization of the output voltage was confirmed. Therefore, if the primary coils are suitably arranged, the power transmission pad can stabilize electric power transmission everywhere.

抄録全体を表示

In order to quantitatively design of repulsive magnets type vibration limit switch, we have derived the vibration parameters which are expressed in vibration equation from experimental results. The vibration parameters are spring coefficient and damping coefficient at switch-on state. The vibration parameters and the structure parameter of switch were related quantitatively as linear and polynomial equations.

抄録全体を表示

A magnetic encoder is an element that detects the moved distance, speed, and rotation angle by sensing magnetism. This has been detected by reading the scale of the magnetic pattern with magnetic sensors. Therefore, it is possible to use these in severe situations such as in liquid and under dust. The magnetic scale of a magnetic encoder is obtained by machining a magnetic substance or by injection molding a plastic magnet. However, it is difficult to obtain the pitch on a detailed scale in the machining. Moreover, a plastic magnet is vulnerable to radiation. We aimed to develop a magnetic scale that was resistant to high temperature and radiation. We combined photolithography and electroplating to form an under 200-micro-meter micro-indentation pattern for the magnetic substance metal and used it as a scale.

抄録全体を表示

This paper describes self-oscillators composed of cantilever type magnetoelastic ribbon resonators as a wireless viscosity sensor. We examined relationship between the viscosity and oscillation amplitude for various mixtures of water and glycerin. The viscosity of 0.314 P could be detected by dipping the edge of the cantilever type resonator into the mixtures. Consequently, we confirmed that a cantilever type ribbon resonator is suitable for measuring viscosity of the high viscosity liquid.

抄録全体を表示

A variable inductor, which consists of only a magnetic core and primary dc and secondary ac windings, can regulate the secondary winding inductance continuously by dc excitation from the primary winding. The variable inductor is expected to be applied to reactive power compensation in electric power systems, because it has a simple and robust structure that is extremely reliable. In a previous paper, a three-phase-laminated-core variable inductor was proposed, which has three-phase secondary ac windings installed in one laminated core to reduce the size and weight in comparison with those of a single-phase variable inductor. This paper presents an experimental verification of the proposed three-phase-laminated-core variable inductor at various ac voltages. The copper and iron losses and the efficiency of the variable inductor are also shown.

抄録全体を表示

Magnetic gears have advantages such as having low acoustic noise and being maintenance-free in comparison with widely-used mechanical gears. This paper deals with a magnetic planetary gear which has inner and outer surface permanent-magnet rotors, and has ferromagnetic-stator pole pieces arranged between both rotors. The magnetic planetary gear has higher transmission torque than other types of magnetic gears since all rotor magnets continuously contribute to generating torque. However, it has not been put into practical use yet. To achieve future practical use, this paper describes a method of improving the efficiency of magnetic planetary gears.

抄録全体を表示

A switched reluctance (SR) motor has salient stator and rotor poles. Concentrated windings individually turn around all stator poles, while the rotor pole has no windings or magnets. Therefore, the SR motor has the following features: a simple and robust structure, large thermal resistance, faster rotation, and low-cost construction. To improve the output power and efficiency of rotating machines, investigations into various materials have recently been conducted to replace conventional non-oriented silicon steel such as grain-oriented silicon steel and soft magnetic composites (SMCs). This paper investigates the possibility of utilizing SR motors made of permendur. We estimated the torque-current characteristics, iron-loss characteristics, and the efficiency of an SR motor using the finite element method (FEM). Furthermore, a suitable structure for SR motors made of permendur is proposed.

抄録全体を表示

In a previous paper, we proposed a magnetic oscillation type dc-ac converter with sinusoidal output. An ac-voltage source is connected to an excitation winding of the magnetic circuit in series. The converter 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 controlled winding of the magnetic circuit according to the law of equal ampere-turns. This converter could be used in an electric-power interconnection system. This converter, however, does not have enough power conversion efficiency for practical use yet. In this paper, we present a new magnetic oscillation-type dc-ac converter with improved efficiency. The basic characteristics of the converter are described in this paper.

抄録全体を表示

This paper discusses the anomalous eddy current caused by magnetic domain wall movement. The anomalous eddy current due to the change of flux space harmonics distribution generated by domain wall movement is generally not affected by steel thickness, but by crystalline grain size. Then, if magnetic flux is concentrated at the steel sheet surface, such as the skin effect, the anomalous eddy current loss increases and weakens the skin effect although classical eddy current decreases. Therefore, it is necessary to use the magnetization curves, taking into consideration the anomalous eddy current loss to estimate the actual eddy current loss, because anomalous eddy current loss cannot be calculated with the usual method, where the DC hysteresis loop is used and microscopic flux distribution is not considered in Maxwell's equation.

抄録全体を表示

Some therapeutic methods of cancer therapy have been developed. Of these, we tried soft-heating hyperthermia. We created a thermosensitive magnetic powder coated with Ag as a heater for cancer therapy. This powder can generate more heat due to losses through hysteresis and inductive current than magnetic powder alone. We could also control the temperature of the heater by using the Curie point. Consequently, we used thermosensitive magnetic powder coated with Ag. This powder composed of Ni-Cu-Zn ferrite granules and Ag was used as the heater for hyperthermia. The Ag coating was achieved by baking Ag paste on the powder. We examined what effect the metallic thickness had in relation to the thermosensitive magnetic powder coated with Ag for cancer therapy. We confirmed that we could increase the heating properties of the powder by selecting the metallic thickness.

抄録全体を表示

Several cubic shaped single crystals of magnetite (40 ± 6 nm) were encapsulated in spherical polymer shells of 184 ± 9 nm diameter. They were used as magnetic carriers for affinity screenings of bioreceptor molecules (proteins) and their “affinity-partner” chemicals. The surfaces of the carrier particles were coated with poly-GMA, which suppressed non-specific chemical adsorption of molecules onto the carrier surfaces. This coating enabled high purity affinity screening. Rapid (for ca. 5 min.) magnetic separation of the carrier magnetic beads, as well as simultaneous processing of 96 samples, enabled automated high throughput screening. The strong resistance of FG beads to organic solvents enables them to conjugate with drugs, which are mostly hydrophobic. Finally, we describe the molecular mechanism of anticancer drugs, MTX and several porphyrins based on our identification of their bioreceptors by our bioscreening system.

抄録全体を表示