The influence of patterned magnetic film size on edge printing characteristics was investigated using micromagnetic simulation. When the track width of the patterned magnetic film was narrower than the desired track width, the printing characteristics were improved. It was revealed that the tolerance for printing characteristics decreased as the magnetic film thickness became thinner, although the printing characteristics under the optimum printing field did not depend on magnetic film thickness.

抄録全体を表示

  The magnetization distribution of a hard disk recorded with magnetic printing and a recording head were compared by utilizing micromagnetic simulation. The servo-signals were modeled with a line and space (L/S) pattern and a checker pattern in this study. The fidelity of recording for L/S and checker patterns were the similar for both methods. As a result, we found that the recording fidelity in magnetic printing was equal to that in head recording though both recording field strength and the gradient in magnetic printing were less than those for head recording. This is because magnetic printing has no recording demagnetization.

抄録全体を表示

  We investigated noise spectra in the GHz range of tunneling magnetoresistive (TMR) read heads with resistance area product (RA) values of 4.0 and 1.7 Ω·μm² in order to understand the influence of spin torque on the noise in these TMR heads. Strong noise spectral peaks were observed at 4.2 and 6.5 GHz in TMR heads with respective RA values of 4.0 and 1.7 Ω·μm². Each peak intensity was enhanced with increasing external magnetic field depending on its polarity when bias current flowed from a free layer to reference one. These results mean that the spin torque influences the thermally excited magnetization fluctuation noise (thermal mag-noise) from the free layers. The peak became sharper and its intensity was enhanced with increasing current density up to 2.7 × 10¹¹ A/m² depending on its direction when the magnetization of free and reference layers were nearly anti-parallel to each other. These results demonstrate that the influence of spin torque on the thermal mag-noise becomes stronger as the current density increases.

抄録全体を表示

  We carried out oblique-incidence sputtering and analyzed in detail the growth mechanism necessary to achieve both good magnetic isolation and a reduction of the Ru interlayer thickness. The results revealed that : (1) Ru grains in the obliquely sputtered Ru thin film possessed a c -plane sheet texture due to epitaxial growth on seed layer grains, and deep gaps were observed at the grain boundaries ; (2) evaluation of the magnetic properties of the magnetic layer deposited on obliquely and conventionally sputtered Ru films suggests that magnetic isolation was enhanced by oblique-incidence sputtering ; (3) an obliquely sputtered pseudo-hcp PdW, CoCr interlayer also enhanced the magnetic isolation of the subsequent magnetic layer ; (4) following the initial growth of a continuous Ru film 1 nm thick, the grains grew, whereas by the conventional method this initial continuous Ru film grew to a thickness of 8nm, showing clear suppression of the continuous Ru layer by oblique-incidence sputtering, and (5) the media using an obliquely sputtered Ru interlayer showed V_act/V_grain = 1.9 with a top layer thickness of 8 nm ; thus, it was possible to reduce the Ru interlayer thickness by suppressing the constitution of the bottom layer.

抄録全体を表示

  In this study, the bit printing characteristics of line and space (L/S), checkerboard, and dot patterns were compared in experiments. The results indicated that the peak-to-peak values of the MFM output of L/S, checkerboard, and dot patterns were almost the same. The optimum printing field for the L/S pattern was the same as that for the checkerboard pattern, whereas the optimum printing field for the dot pattern was lower than those of the L/S and checkerboard patterns. This is because the maximum value of the recording field in the dot pattern was larger than those of the L/S and checkerboard patterns.

抄録全体を表示

  Recent experiments have suggested a possibility of room-temperature ferromagnetism in graphite-like materials. We analyzed multiple spin states in asymmetric graphene molecules to find the mechanism responsible for ferromagnetism. First principle density functional theory was applied to calculate ground state spin density, energy, and atom position depending on each spin state. Molecules with dihydrogenated zigzag edges like C₆₄H₂₇, C₅₆H₂₄, C₆₄H₂₅, C₅₆H₂₂, and C₆₄H₂₃ indicated that the highest spin state in every molecule is the most stable having an energy difference of kT = 3000 K with the next spin state. In contrast, nitrogen substituted molecules like C₅₉N₅H₂₂, C₅₂N₄H₂₀, C₆₁N₃H₂₂, C₅₄N₂H₂₀, and C₆₃N₁H₂₂ demonstrated opposite results where the lowest spin state was the most stable. The magnetic stability of graphene molecules can be explained through three key factors depending on the edge specified localized spin state, the exchange interaction between parallel spins inside a molecule, and optimized atom position. We intend to apply these results to design carbon-based magnets, ultra high density information storage, and spintronic devices.

抄録全体を表示

  The dependence of saturation magnetization and uniaxial anisotropy constant on current-induced domain wall motion in a magnetic nanowire with perpendicular magnetic anisotropy was analyzed through micromagnetic simulation. The results indicated that the critical current density linearly decreased by reducing the saturation magnetization. Even if the domain wall width was changed by the uniaxial anisotropy constant, the domain wall width did not influence the critical current density since the increase in the domain wall width anisotropy constant caused an increase in the effective wall anisotropy. It was revealed that the decrease in the saturation magnetization was the dominant factor in reducing the critical current density.

抄録全体を表示

  Epitaxial L1₀-ordered FeNi thin films were artificially fabricated on a nonmagnetic AuNi buffer layer by using an alternate monatomic layer deposition. A uniaxial magnetic anisotropy energy of the FeNi layer was estimated to be 5.8 × 10⁶ erg/cm³ from magnetization measurements, which is the largest energy among values reported on FeNi thin films grown on nonmagnetic buffers. A long-range order parameter of the FeNi layer was estimated to be 0.330 from a grazing incidence X-ray diffraction (GI-XRD) using synchrotron radiation. We also investigated the relation between the ratio of c-axis lattice constant to a-axis lattice constant (c/a ratio) and the uniaxial magnetic anisotropy energy of FeNi thin films grown on several buffer layers. The uniaxial magnetic anisotropy energy monotonically increased with the increase in the c/a ratio, whereas the anisotropy had no clear relation with the long-range order parameter. Not only the improved long-range order parameter but optimized c/a ratio in FeNi are expected to lead to the enhancement of the perpendicular magnetic anisotropy.

抄録全体を表示

  Spin-dependent electrical resistivities ρ^↑, ρ^↓ of bcc-Fe based on scattering due to magnetic fluctuation below the Curie temperature were calculated using first-principles methods. The tight-binding linear muffin-tin orbital method with local spin-density approximation was employed to calculate the electronic structure. The spin fluctuations within the static (adiabatic) approximation corresponded to the local spin disorder, which can be treated using the coherent potential approximation. The Kubo-Greenwood formula was used to calculate the electrical resistivity in each spin state based on the electron scattering by magnetic fluctuations. The obtained results indicated that the ferromagnetic states of bcc-Fe in finite temperature are characterized as a classical spin system such as the Heisenberg model, although the electronic structure calculations are carried within the itinerant electrons system. The total electrical resistivities ρ = ρ^↑ρ^↓/(ρ^↑ + ρ^↓) which are on the basis of the two-current model show qualitative agreement with the experimental measurement as a function of temperature. Furthermore, the spin asymmetry coefficients β = -(ρ^↑ - ρ^↓)(ρ^↑ + ρ^↓) exhibited a remarkable behavior that the sign changed from positive to negative in the finite temperature region below the Curie temperature.

抄録全体を表示

  Ferromagnetic materials are widely used for cars, trains, and ships. Because of their mechanical properties, iron and steel are popularly used for the frame materials. Nondestructive testing of iron and steel is an extremely important way of maintaining their mechanical reliability. It is well known fact that Barkhausen signals are only emitted from ferromagnetic materials having magnetic domain structures. Also these signals change their properties depending on their past mechanical as well as radioactive stress histories.
  We applied a method of analyzing frequency fluctuations to the Barkhausen signals to detect the mechanical stresses. We unexpectedly succeeded in finding that applying frequency fluctuation analysis to the Barkhausen signal made it possible to detect the mechanical stress. This was fact confirmed by applying our method to the 30 test ferromagnetic materials. Further, the environmental noise problem essentially accompanying measurement of the Barkhausen signals were taken into account by applying this frequency fluctuation analysis method to environmental noise.

抄録全体を表示

  This paper presents a noise suppression sheet containing magnetic flakes and carbon fibers. Permeability of the magnetic flakes and conductivity of the carbon fibers provide noise suppression effectively in the GHz range. Furthermore, the carbon fibers improve thermal conductivity of the sheet compared with conventional sheets containing only magnetic flakes. The sheet is expected to provide measures for both of electromagnetic noise and thermal problem.

抄録全体を表示

  We have developed a new system for nondestructive inspection (NDI) which enables accurate detection and easy handling at low cost. It works by measuring the impedance due to the change in inductance in a solenoid coil. This paper describes the validity of the method we used to design this NDI system. The change in impedance and phase difference were measured with an impedance meter. The fractional deviation in inductance L and impedance Z changes due to the magnetization induced with and without a steel bar. The reduction in inductance L due to the eddy currents of power cables was measured. The measurement also proved that this NDI system can distinguish steel bars from power cables by using the polarity of the phase difference similar to what occurs in real concrete walls and slabs.

抄録全体を表示

  Variable inductors, which consist of a magnetic core and primary dc and secondary ac winding, can control the effective inductance of the secondary ac winding with primary dc current. Hence, they can be applied to electric power systems to compensate for reactive power. We proposed a three-phase laminated-core variable inductor in a previous paper, and demonstrated that its weight was reduced by more than 30% as compared with the conventional one. However, simulation including a control system is required to apply a variable inductor as a reactive power compensator. We therefore propose a method of calculating the characteristics of a three-phase laminated-core variable inductor using MATLAB/Simulink, which is suitable for the designing and analyzing the control system. We also evaluated a method of controlling the variable inductor with an asymmetric half-bridge converter.

抄録全体を表示

  In recent years, designing and analyzing of permanent magnet (PM) motors taking into consideration magnetic nonlinearity and eddy current loss in rare-earth magnets has increased in importance since the PM motors are driven by a three-phase PWM inverter and the working flux density is very high. In previous papers, we proposed a method for calculating the characteristics of PM motors based on reluctance network analysis (RNA). The proposed RNA model of the PM motors can be coupled with the inverter and mechanical system. Using the proposed model, we accurately calculated the iron loss in the stator core of the PM motor. However, the eddy current loss in the permanent magnets caused by carrier harmonics and slot harmonics was not discussed. We present here a method for calculating the eddy current loss based on an electric network that can be coupled with the RNA model. To verify the validity of the proposed method, the estimated values are compared with those obtained using a finite element method (FEM) and an experiment.

抄録全体を表示

  Radiation is one treatment for cancer, and it is used together with other therapies. The accuracy of irradiation has recently improved due to advances in image diagnosis processors such as CT, MRI, and external irradiation machines. However, real-time data on internal doses near the focus are required to treat cancers effectively. Therefore, an implantable dosimeter with a wireless signal transmission system is needed. The dosimeter also needs a wireless power feeding system to drive the internal circuit. However, depending on where the internal elements are placed, there may be cases when power feeding cannot be achieved with conventional solenoid or spiral coils. To solve this problem, we suggest a new model for the feeding coil that can generate multi-directional excitation. If the feeding coil can generate multi-directional excitation, we can supply sufficient power to drive the internal circuit to the internal element. We studied an external feeding circuit and measured the feeding area where we could supply power to the internal element regardless of the position or direction of the internal elements that had been installed.

抄録全体を表示