CoCrPtO-based granular composite perpendicular recording media

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