摘要
The microscopic mechanism of coercivity at finite temperature is a crucial issue for permanent magnets.Here we present the temperature dependence of the coercivity of an atomistic spin model for the highest-performance magnet Nd_(2)Fe_(14)B.For quantitative analysis of the magnetization reversal with thermal fluctuations,we focus on the free energy landscape as a function of the magnetization.The free energy is calculated by the replica-exchange Wang–Landau method.This approach allows us to address a slow nucleation problem,i.e.,thermal activation effects,in the magnetization reversal.We concretely observed that the thermal fluctuations lead to a downward convexity in the coercivity concerning the temperature.Additionally,through analyzing the microscopic process of the thermal activation(nucleation),we discover the activation volume is insensitive to a magnetic field around the coercivity.The insensitivity explains the linear reduction of the free energy barrier by the magnetic field in the nucleation process.
