Magnetization reversal and stochastic behavior in CoCrPt alloy thin films

Abstract

Magnetization reversal behavior and domain dynamics in ultrathin ferromagnetic films are fundamentally crucial issue, since magnetization reversal behavior and domain dynamics play important role in determining their important magnetic properties such as the shape of magnetic domain and the coercivity. It is also an important subject in technological point of view, because it governs the formation of the written domain size, irregularity, and stability. We have investigated the magnetization reversal behavior, stochastic behavior in magnetization reversal process, and their scaling behavior in CoCrPt alloy films, which has received significant attention as possible high-density perpendicular magnetic recording media because of its strong perpendicular magnetic anisotropy and high coercivity necessarily required for high-density recording. In our study, we utilized the full-field magnetic transmission soft X-ray microscope (MTXM), which has a lateral resolution down to 15 nm provided by Fresnel zone plates used as optical elements and magneto-optical microscope magnetometer (MOMM), capable of direct time-resolved observation of magnetic domain patterns and simultaneously measuring the local magnetic properties on a submicrometer spatial resolution. We report that the magnetization switching is carried out by a random nucleation process that can be attributed to individual grains. We found evidence of a large distribution of the switching fields at the nanogranular length scale, which has to be considered seriously for applications of CoCrPt systems as magnetic high density storage materials. We found that with increasing the Pt concentration the local coercivity distribution becomes asymmetric and the average local coercivity as well as the width of the distribution increases. Transmission electron microscopy studies, together with a theoretical explanation reveal that the results are closely correlated with the grain size distribution dependent on the Pt conc...