Coercivity mechanism in CoPt alloy films with perpendicular magnetic anisotropy (abstract)

Abstract

The coercivity is one of the key parameters for defining a suitable magneto-optic recording material. In order to get insight into coercivity mechanisms we have studied the magnetization reversal processes by means of magneto-optic methods in CoPt alloy films. These films were prepared in UHV by coevaporation with a typical composition ratio of Co28Pt72 and show excellent perpendicular magnetic anisotropy at elevated substrate temperatures during deposition. STM and x-ray measurements reveal characteristic grain size of about 15–20 nm and dispersion of crystallite axis of the order of 0.5°, respectively, which varies only slightly with total film thicknesses of 5–50 nm. The magnetization reversal processes are investigated by using polar Kerr microscopy and were found to be dominated by domain formation and domain wall propagation. A micromagnetic model was developed which describes the film as an ensemble of single domain particles. The size of these single domain particles was chosen to be of the order of the average grain size. In the numerical simulation we include dipolar interaction and domain wall energy contribution. The comparison of the results of the simulation with the experimental results clearly points out that the microstructure is responsible for the magnetization reversal behavior. A thermal as well as thermally activated magnetization processes contribute to the reversal mechanism. The coercivity is predominantly determined by pinning on grain boundaries.