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-performanc...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.展开更多
文摘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.
