Proposal of Granular-Type Cap Layer with High-K_u CoPt Grains and Ferromagnetic Oxide Grain Boundaries for Full Granular Media

Investigation of magnetic properties and microstructure for the stacked media with Co₈₀Pt₂₀-30 vol% rare earth (RE) oxide (RE oxide: Gd₂O₃, Nd₂O₃, and Sm₂O₃) cap layers (CLs) deposited on a Co₈₀Pt₂₀-30 vol% B₂O₃ granular recording layer (GRL) was conducted. It was found that the employment of a granular-type CL with ferromagnetic oxide is effective to control intergranular exchange coupling of the magnetic grains in CoPt-B₂O₃ GRL while maintaining the granular structure of the CL. In this full granular media, continuous structure of columnar magnetic grains and grain boundaries from the GRL up to the CL can be observed. When a typical ferromagnetic oxide CL, such as CoPt-Gd₂O₃ (9 nm), is deposited on CoPt-B₂O₃ GRL (16 nm), the nucleation field is increased from 0.7 to 1.1 kOe, and the saturation field is reduced from 21.5 to 16 kOe which suggest that CoPt-RE oxide is promising for a CL.