Magnetic films with high perpendicular magnetic anisotropy (PMA) are crucial for developing gigabit spin-transfer-torque magnetic random access memory, making it practically important to investigate Gilbert damping for various films exhibiting PMA. It is also interesting to explore the physics related to the spin-orbit interaction behind Gilbert damping in magnetic materials with strong spin-orbit interactions, as it is also a source of high magnetic anisotropy. In this paper, we review our optical studies on Gilbert damping for various PMA films and discuss the underlying physics.

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  An anisotropy constant K_u required for thermally assisted magnetic recording (TAMR) was calculated. First, a heat transfer simulation was carried out to obtain the thermal gradient of media at the time of writing for the K_u calculation. Both the Curie temperature T_c and K_u should be designated for TAMR media design. K_u is a function of T_c. Therefore, we introduce a parameter K_u / K_bulk that shows the intrinsic ratio of film K_u to bulk K_u. From the information stability conditions, we estimated whether or not the media have the potential for TAMR. The limiting factor is the thermal gradient related to the information stability on the trailing side located 1 bit from the writing position during writing and at the adjacent track during rewriting, and the limiting factor determines the minimum K_u / K_bulk. Therefore, the minimum K_u / K_bulk strongly depends on the thermal gradient. Consideration was also given to the dependence of the grain number per bit on K_u / K_bulk, the dependence of the standard deviation of the grain size on K_u / K_bulk, the dependence of the thickness of the recording layer on K_u / K_bulk, and the dependence of the writing temperature on K_u / K_bulk.

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  CoPt and Co₃Pt alloy epitaxial films with the close-packed plane parallel to the surface are prepared on MgO(111) single-crystal substrates heated at 300 °C by varying the film thickness in a range between 2 and 40 nm. The structure is investigated from the viewpoints of the order degree and the atomic stacking sequence of close-packed plane. Metastable ordered phase formation is recognized for both CoPt and Co₃Pt films. The CoPt and the Co₃Pt films involve L1₁ and B_h(+D0₁₉) phases, respectively. Higher order degrees are recognized for thicker CoPt and Co₃Pt films. As the thickness increases, the strain caused by accommodation of the lattice mismatch between film and substrate decreases. The ratios of out-of-plane to in-plane lattice spacings, 2d_L11(222) / 2d_L11(440) and 2d_{Bh(+D019)(0002)} / 2d_{Bh(+D019)(2240)}, of CoPt and Co₃Pt films, respectively, decrease from 1.638 to 1.630 and from 1.637 to 1.616 with increasing the thickness from 2 to 40 nm. The films involving metastable phases show strong perpendicular magnetic anisotropies reflecting the magnetocrystalline anisotropies of L1₁ and B_h(+D0₁₉) crystals.

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  Dual-Halbach arrayed permanent magnets were produced with Dy-free Nd bonded permanent magnets whose external dimensions were 14×14×4 mm. The dual-Halbach magnets were arranged facing different poles with a 6-mm-distance air gap using the back yoke. The magnetic flux density at the center of the air gap was measured with a two-axis Hall prober and was also numerically calculated with the three-dimensional finite-element method. The flux density was enhanced with the front yoke by 9% compared to that without the front yoke. The front yoke also improved the irreversible flux loss after high temperature annealing. Furthermore, a 2.2% increase was successfully achieved with fragmentation of the back yoke. The calculated three-dimensional flux structure indicated that the efficient magnetic circuits with less stray flux to the outside enabled further enhancement of the flux density even in magnet arrays that involved complex multi-poles.

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  Wireless power transfer (WPT) systems transmit electrical power to devices via a high-frequency electromagnetic field. The load conditions of devices change dramatically depending on their operating conditions; however, these systems must supply a constant output voltage that is stable regardless of the load. This paper describes a method of using the LC-booster to stabilize the output voltage while maintaining efficiency. The LC-booster contains two secondary coils, where one is connected to the load and the other is connected to the capacitor to create a resonator. This allows the optimized load of the LC-booster to be adjusted. We demonstrate that the LC-booster can stabilize output voltage over a wide range of loads and is thus a promising method of versatile stabilization method.

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  This paper presents a feasibility study of an in-wheel magnetic-geared motor for walking support machines. The proposed magnetic-geared motor consists of an axial-gap permanent magnet (PM) motor and a magnetic gear. Axial-gap PM motors generally have larger torque than conventional radial-gap motors when their structures are flat like those in in-wheel motors. Moreover, the axial-gap PM motor was combined with magnetic gears since the in-wheel motor requires further large torque at low speed. The characteristics and usefulness of the proposed magnetic-geared motor are demonstrated through experiments and analysis conducted using finite element method (FEM).

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