Switching Behavior and Writeability in Perpendicular Magnetic Dual Oxide Media With Capping Layer

We report a systematic study of the switching behavior and writeability characteristics of perpendicular magnetic recording media in which the anisotropy (K_u) of granular oxides, magnetic volume (M_s·t, product of magnetization and thickness) of cap layer, and exchange coupling between granular oxide and cap layer were varied. The media switching behavior highly depends on the M_st of cap layer as well as the oxide-to-cap exchange coupling strength but little on the K_u of granular oxides. The media switching field H_o at 1-ns scales is strongly affected by switching mode and is greatly reduced with incoherent switching mode. At constant switching mode with fixed M_st of cap layer, the media writeability is primarily determined by the oxide K_u value that affects the H_o. However, when the switching mode varies with different cap M_st or oxide-to-cap exchange coupling strength, no correlation between H_o and writeability is observed. Higher K_u oxide media with higher M_st of cap layer exhibits lower H_o due to more incoherent switching but substantially lower overwrite (OW) than the lower K_u oxide media with lower M_st of cap. Similarly, media with weaker exchange-coupling between oxide and cap layers shows more incoherent switching mode and worse writeability even with lower H_o. Our results have shown that oxide-to-cap exchange coupling as well as oxide K_u is critical in media design for good writeability at high recording density and can be optimized through selection of appropriate oxide and cap materials.