Coercive field and energy barriers in partially disordered FePt nanoparticles

Partially disordered FePt nanoparticles prepared by the sputtering method and protected by Al2 O3 constitute an interesting realization of graded media, recently suggested for future generations of magnetic recording. By depositing the alumina layer, the particle is partially disordered with gradually varying properties. The current work comprises a comparison between experimental data and atomistic modeling results of the coercive field and energy barriers in FePt particles with gradually spatially varying properties, specifically the magnetization, anisotropy, and exchange constants. From our modeling we conclude that the magnetization reversal processes for dynamic reversal at the coercive field and for the zero field energy barrier involve different reversal modes. The coercive field decreases as a function of disordering length up to 2 T and is in good agreement with measured values. The zero field energy barrier, except for highly disordered particles, is almost independent of the disordering length, retaining the high values required for thermal stability.