Magnetic properties of granular-type FePt-MgO perpendicular recording media

Granular-type FePt films with perpendicular magnetic anisotropy are fabricated onto glass substrates by annealing FePt/MgO multilayer films. The uniaxial perpendicular magnetic anisotropy constant (K_u) and the activation volume (V^*) are obtained by fitting the remanent coercivity as a function of the applied field waiting time using the Sharrock´s formula for oriented magnetic grain assembly. K_u increases with annealing temperature and annealing time, as a result of the enhanced chemical ordering in L1₀ phase FePt grains. V^* tends to decrease with annealing time revealing the FePt grain separation process by the MgO matrix with annealing. By modifying the initial FePt/MgO multilayer structure and annealing condition, the optimized FePt-MgO film shows a high K_u and a small V^* value.