The review covers the research and development of perpendicular media nanostructure focusing on the recording layer. The recording layer material includes the Co-alloys with hcp structure, the magnetic multilayers, and the alloys with ordered structures that have high magneto-crystalline anisotropies (K_u). The technologies of underlayer or interlayer for aligning the easy magnetization axis of magnetic crystal grain perpendicular to the film plane are briefly reviewed including the high K_u magnetic materials for future recording media.

  Observations of compositional and magnetization structures in sub-μm scale have played important roles in improving the recording layer. Typical data on these characteristics are explained in relation to the media structure improvements. Considering that high K_u magnetic materials will be employed in future recording media, basic experimental results related in controlling the easy magnetization axis and in keeping the surface flatness of L1₀-ordered magnetic materials are explained. Future possibilities for increasing the areal density beyond 1 Tb/in² by improving the magnetic material and the nanostructure of recording layer are also discussed.

  We report the synthesis of (Zn²⁺Ti⁴⁺) substituted hexagonal ferrites, BaZn₂(Zn_0.5Ti_0.5)_xFe_16-xO₂₇ (W-type) and Ba₂Zn₂(Zn_0.5Ti_0.5)_xFe_12-xO₂₂ (Y-type), and the relationship between their composition and magnetic properties. Substituted W-type ferrite was synthesized in the region of 0.0 ≤ x ≤ 1.5. A decrease in the Curie temperature of the W-type phase indicated that the exchange interactions between the Fe³⁺ ions weakened due to the substitution of Zn²⁺ and Ti⁴⁺ ions. Spontaneous magnetization (σ_S) at x = 0.5 was similar to that at x = 0.0. This reflects the equal distribution of nonmagnetic Zn²⁺ and Ti⁴⁺ ions to spin down sites and spin up sites, respectively. At x > 0.5, σ_S decreased clearly, which was possibly caused by a deviation from the collinear arrangement. Substituted Y-type ferrite was also obtained up to x = 0.5. The Y-type phase is more unstable than the W-type phase with respect to this substitution rate.

  We describe a low permeability composite magnetic core transformer with a high coupling coefficient and its application to a PFM controlled quasi-resonant mode flyback-type DC-DC converter. To increase the coupling coefficient between primary and secondary windings embedded in a carbonyl-iron powder/epoxy composite magnetic core with a relative permeability of 6, three types of winding layouts were investigated by using a 2D-FEA numerical simulation and the characteristics were confirmed experimentally. The primary and secondary windings that were laid out adjacent to each other were the best choice as it had the highest coupling coefficient at over 0.99. By applying the composite magnetic core transformer with this coupling coefficient to a 48 V input/12 V output PFM controlled quasi-resonant mode flyback-type DC-DC converter, the maximum efficiency was 92.5% at an output power of around 28 W, and an efficiency of 90.0% was obtained at an output power of 60 W.