High K_u and small grain size Co₈₀Pt₂₀ granular media with double oxide grain boundary materials consisting of B₂O₃

Investigation of magnetic properties and microstructure of granular media with various double oxides including B₂O₃ as the grain boundary material is reported. By adding a high T_m second oxide together with B₂O₃ for the grain boundary material, comparable magnetic properties with that of the single oxide granular media and smaller crystallite size evaluated by X-ray diffraction (GD_inplane) than that of the single oxide granular media can be obtained. Among the evaluated media, the granular medium with B₂O₃− TiO₂ is promising for the grain boundary material, showing comparable average M_s and K_u of 806 emu/cm³ and 7.7×10⁶ erg/cm³ with that of the single B₂O₃ and smaller GD_inplane of 4.8 nm than that of the single B₂O₃ of 5.4 nm. In the TEM image, thin grain boundaries inside the grains can be observed which indicates that small grains with one-on-one grains growth is expected when an underlayer with smaller grain size is utilized.