Power law analysis for temperature dependence of magnetocrystalline anisotropy constants of Nd2Fe14B magnets

Daisuke Miura,Akimasa Sakuma

doi:10.1063/1.5021969

Abstract

We perform phenomenological analysis of the temperature dependence of magnetocrystalline anisotropy (MA) in rare-earth magnets. We define the phenomenological power laws applicable to compound magnets using the Zener theory, and we apply these laws to study the magnetocrystalline anisotropy constants (MACs) of Nd2Fe14B magnets. The results indicate that the MACs closely obey the power law, and further, our analysis yields a better understanding of the temperature-dependent MA in rare-earth magnets. Furthermore, to examine the validity of the power law, we discuss the temperature dependence of the MACs in Dy2Fe14B and Y2Fe14B magnets as examples of cases wherein it is difficult to interpret the MA using the power law.

Highlights

The complex behaviors of magnetic anisotropy (MA) in rare-earth permanent magnets have attracted considerable research attention, since such magnets are widely used as high-performance magnets that combine high magnetocrystalline anisotropy with reasonable magnetization and Curie temperature.[1,2,3,4] Typical examples of such magnets include R2Fe14B magnets, which form the focus of the present study
We have previously confirmed that an effective Hamiltonian using the parameters suitably describes the experimental temperature dependence of the magnetocrystalline anisotropy constants (MACs) of Nd2Fe14B magnets.[9,10]
We have shown explicit forms of the power law applicable to rare-earth magnets within the framework of the Zener theory, and we have demonstrated that the power law suitably describes the experimental MACs of Nd2Fe14B magnets

Summary

INTRODUCTION

The complex behaviors of magnetic anisotropy (MA) in rare-earth permanent magnets have attracted considerable research attention, since such magnets are widely used as high-performance magnets that combine high magnetocrystalline anisotropy with reasonable magnetization and Curie temperature.[1,2,3,4] Typical examples of such magnets include R2Fe14B magnets (where R denotes a rare-earth element), which form the focus of the present study. The total magnetic moment of R2Fe14B magnets is the sum of the R moments and the Fe moments; in the case that the directions of both moments are mutually non-collinear, the temperature dependence of the MACs will not obey the power law, and we can no longer regard the magnetic structure as a uniform one In this regard, Dy2Fe14B magnets are typical examples exhibiting high non-collinearity because of the antiferromagnetic coupling existing between the Dy and Fe moments,[1,18] and further, a wide plateau has been found in the temperature-dependence curve of their first-order MAC in the low-temperature range.[20,21] In contrast, in Nd2Fe14B magnets, it is possible to assume that the Nd moments are collinear with the Fe moments.[18,22]. We briefly discuss the applicability of this law to Y2Fe14B and Dy2Fe14B magnets

POWER LAW FOR MACS IN TETRAGONAL SYMMETRY

TEMPERATURE DEPENDENCE OF MACS IN R2Fe14B MAGNETS

SUMMARY