The influence of the initial magnetization of a perpendicular anisotropy master medium (PAMM) on bit printing characteristics was investigated through experiments. As a result, the initial magnetization of PAMM affected magnetic printing characteristics for a bit length of 150 nm. Here, the best magnetic printing characteristics were obtained when PAMM was initially magnetized in the direction of the printing field. However, for a bit length of 200 nm, the initial magnetization of PAMM had little influence on magnetic printing characteristics.

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  We developed a dynamic thermal and micromagnetic model for thermally assisted magnetic recording, which employed Landau-Lifshitz-Bloch equation for the thermo-dynamic magnetization motion. It has shown completely different switching mechanism at high temperature compared to that from the Landau-Lifshitz-Gilbert equation. This results, in part, from the assumption in the Landau-Lifshitz-Gilbert equation that the magnetization vector length is conserved at any temperature. In view of the fact that the Garanin's Landau-Lifshitz-Bloch model does not have this constraint, it can estimate the switching field and switching speed in including around Curie temperature. Since thermally assisted magnetic recording is near Curie temperature recording, Landau-Lifshitz-Bloch equation must be suitable for the model of this recording process.

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  DC-biased magnetic properties of powder cores made of pure iron powder have been investigated using a nonmagnetic grain boundary (NMGB) model taking into account the distribution of gap width between particles. Three kinds of powder were prepared by water atomization (a), sphericalization (b), and gas atomization (c). Various amounts of additives were added to (a) to investigate the gap width effect between the particles on the powder core (aa). B-H loops were measured, and differential permeability (μ_dif) was calculated at each magnetic field. They were compared with the value calculated from the NMGB model taking into account the gap width distribution. The more spherical particles were, the lower the μ_dif was at low magnetic field, and the smaller the fall rate of μ_dif was at high magnetic field. That indicated the DC-biased magnetic properties improved. From the calculation using the NMGB model, the geometric average value (δ_gave) of the gap width increased, and the geometric standard deviation(σg) decreased. The effect of μ_dif on DC-biased magnetic properties was also investigated. The greater the amount of aluminum oxide added to (a), the larger δ_gave became, the smaller σ_g became, and the smaller decreasing ratio of μ_dif at 6 k A/m against 0 k A/m became. However, the decreasing ratio of μ_dif(C) was smaller than that of (b). Relative inaccuracies for all samples between measured and calculated μ_dif were under ±6.20% at a magnetic field 0.6-17 k A/m .

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  Co thin films were prepared on Al₂O₃ single-crystal substrates with (0001) and (11-20) orientations by ultra-high vacuum molecular beam epitaxy. Effects of substrate temperature and substrate orientation on the film structure were investigated. Co epitaxial thin films with close-packed planes parallel to the substrate surfaces are obtained on Al₂O₃(0001) and Al₂O₃(11-20) substrates at 50-500 °C and 300-500 °C, respectively. The films grown on Al₂O₃(0001) substrates at temperatures lower than 100 °C consist of fcc-Co(111) crystal. With increasing the substrate temperature, hcp-Co(0001) crystal begins to coexist with the fcc crystal and the volume ratio of hcp to fcc crystal increases. The films grown at temperatures higher than 300 °C consist primarily of hcp crystal coexisting with a small volume of fcc crystal. On the contrary, the Co thin films grown on Al₂O₃(11-20) substrates at temperatures higher than 300 °C consist of only the hcp crystal. The in-plane lattice strains of these Co epitaxial films are larger than the out-of-plane lattice strains due to the accommodation of lattice mismatches between the films and the substrates. The film strain decreases as the substrate temperature increases.

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  We have designed a hybrid dc-dc converter that includes a four-legged transformer and alternately operates as forward and flyback converters. To miniaturize dc-dc converters, it is necessary to reduce the ripple current that flows through output smoothing capacitors. A transformer applied to the hybrid dc-dc converter has a particular air-gap length that reduces the ripple current of the output smoothing capacitors during forward and flyback operations. We applied the air-gap length conditions to four-legged transformers as well as EI core transformers and experimentally obtained the output current ripple characteristics.

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