CoCrPtO-Based Granular Composite Perpendicular Recording Media

The effect of capping layer thickness (t_Cap) on media properties in CoCrPtO-based granular composite media is investigated. The CoCrPt-based capping layer with much less coercivity (H_c) and more exchange coupling than the bottom layer was used. Surprisingly, H_c increases from 4.9 to 5.9 kOe with increasing t_Cap from 0 to 3.8 nm (Zone I) and then decreases to 4.1 kOe at t_Cap=8.3 nm (Zone II). As t_Cap increases, the a axis lattice constant increases from 2.584 to 2.592 Aring, while the c axis lattice constant decreases from 4.213 to 4.192 Aring. Zone I exhibits relatively constant loop slope (alpha) at H_c and activation volume (Vact) for magnetic reversal, while Zone II shows the increase in alpha and V_act. This increase is confirmed by TEM images with less grain isolation and larger grain size. Angular dependence of H_cr in Zone II shows less coherent switching behavior compared to Zone I. Thermal stability factor continuously improves from 59 to 107 with increasing t_Cap. Simulation results reveal that the increase in H_c at Zone I is mostly due to the enhancement of thermal stability. The decrease in H_c at Zone II is understood as a dynamic tilted medium caused by the increase in lateral exchange coupling in the capping layer