An atomistic model of switching in FePt nanoparticles

A model of the magnetic properties and magnetisation reversal mechanisms in nano-particulate FePt is presented. The model is based on the development of an effective spin model of magnetic interactions constructed and parameterized from ab-initio electronic structure calculations. The model is shown to give good agreement with experiment for the static magnetic properties, including the variation of K with M and Curie temperature. The model is also extended to investigate dynamic magnetic properties such as high sweep rate switching and thermal magnetization relaxation. It is shown, within the atomic scale Langevin dynamic approach, that the Neel-Brown relaxation time works reasonably well as long as the temperature dependence of the intrinsic parameters is taken into account. The contributions of thermal and athermal finite size effects to the relaxation time and the critical FePt size are investigated within the proposed model of magnetic interactions and using first-principles calculations of free [001] and (111) surfaces.