Cr₂O₃ is a magnetoelectric antiferromagnet, and its antiferromagnetic domain state is controllable by the simultaneous application of magnetic and electric fields. In the 2000s, that is, more than 50 years since the discovery of the magnetoelectirc effect in Cr₂O₃, efforts were initiated apply this effect to engineering applications. In this article, we review the recent progress of the magnetoelectric control of the antiferromagnetic domain state and the related phenomena of Cr₂O₃, in particular, in an all-thin film system, an essential step to the application.

  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.

  Various transition-metal magnetic materials have been investigated from basic and practical viewpoints. The concentration dependence of the Néel temperature T_N of Cr-based alloys is complicated. Cr-Si and Cr-Fe antiferromagnetic alloys show Invar characteristics in the ternary alloys. Fe-based amorphous alloys exhibit weak ferromagnetic properties, resulting in remarkable magnetovolume effects. The icosahedral quasicrystals containing Mn show a spin-glass behavior, in a similar manner as those of amorphous counterparts. Itinerant-electron metamagnetic transition occurs in La(Fe_xSi_1-x)₁₃, accompanied by many drastic change in magnetic and elastic properties. These drastic changes are practically useful in the field magnetic refrigeration and linear magnetostriction. The magnitude of T_N of Mn-based γ-phase is increased by addition of Ir, Ru, Rh and the spin structures change, depending on temperature and composition. Several kinds of L1₀-type Mn alloys have a high value of T_N with a large magnetocrystalline anisotropy. The shift of the exchange-bias field for the collinear spin structure in L1₀-type phase is induced by spin frustration. L2₁- and B2-type Co₂CrGa metallurgical stable alloys exhibit a high spin polarization. Several kinds of L2₁-type and B2-type alloys show a large ferromagnetic shape memory effect associated with twin-boundary motions.

  L1₀-type alloys and L2₁-type Heusler alloys are key materials for future spintronic and magnetic storage devices. L1₀-FePt with high uniaxial magnetic anisotropy is a promising material for ultrahigh density recording because of its high thermal stability of magnetization at a nanometer scale. Co-based Heusler alloys showing high spin polarization of conduction electrons enable us to enhance the magnetoresistance effect. In addition, utilizing the magnetization dynamics in these ordered alloys provides us with new paths in the development of spintronic and magnetic storage devices. In this review, we introduce the control of magnetization switching field for L1₀-FePt exchange-coupled with Ni₈₁Fe₁₉ by utilizing the spin waves in the bilayers, which will be useful for information writing. A nanometer-scaled rf oscillator is also introduced, in which the magnetization dynamics is excited by spin angular momentum transfer. We can improve both the rf output power and the oscillation quality simultaneously by using Co₂(Fe_0.4Mn_0.6)Si Heusler alloy.