Qualitative Insight and Quantitative Analysis of the Effect of Temperature on the Coercivity of a Magnetic System

TL;DR

This paper combines qualitative and quantitative methods to analyze how temperature affects the coercivity of a Fe/Sm-Co spring magnet, emphasizing the role of thermal activation in magnetic transitions.

Contribution

It introduces a 2D energy surface model that explains and reproduces the temperature-dependent coercivity without changing model parameters.

Findings

Hysteresis loop width halves from 25K to 300K

Thermal activation over energy barriers explains coercivity reduction

Applied magnetic field modifies transition pathways

Abstract

The temperature dependence of the response of a magnetic system to an applied field can be understood qualitatively by considering variations in the energy surface characterizing the system and estimated quantitatively with rate theory. In the system analysed here, Fe/Sm-Co spring magnet, the width of the hysteresis loop is reduced to a half when temperature is raised from 25~K to 300~K. This narrowing can be explained and reproduced quantitatively without invoking temperature dependence of model parameters as has typically been done in previous data analysis. The applied magnetic field lowers the energy barrier for reorientation of the magnetization but thermal activation brings the system over the barrier. A 2-dimensional representation of the energy surface is developed and used to gain insight into the transition mechanism and to demonstrate how the applied field alters the transition path. Our results show the importance of explicitly including the effect of thermal activation when interpreting experiments involving the manipulation of magnetic systems at finite temperature.