Effect of thermal fluctuations on magnetization reversal of L10 FePt nanoparticles

Abstract

The temperature-dependent switching field, magnetic viscosity and activation volume of L10 FePt nanoparticles with size ranging from 3 to 15 nm have been studied systematically. It is found that the anisotropy constant increases with particle size which is attributed to size-dependent chemical ordering. The temperature dependence of magnetic viscosity and activation volume can be well explained for the 3–8 nm particles by the Stoner–Wohlfarth model incorporating thermal activation, but the model is not suitable for the 15 nm particles. A quantitative analysis of the relation between the switching field and activation volume suggests that the magnetization in the single-crystal 3–8 nm particles reverses via coherent rotation. However, the magnetization reversal in polycrystalline 15 nm particles cannot be well described by coherent rotation although the particle size is much smaller than the single-domain size derived from bulk L10 FePt magnetic material, which may be due to the multiple crystals within each nanoparticle.