Theoretical evaluation on the temperature dependence of magnetic anisotropy constants of Nd2Fe14B - Effects of exchange field and crystal field strength -

TL;DR

This paper theoretically investigates how the exchange field and crystal field strength influence the temperature dependence of magnetic anisotropy constants in Nd2Fe14B, shedding light on coercivity degradation mechanisms.

Contribution

It introduces a theoretical analysis of the effects of exchange field variations on magnetic anisotropy constants in Nd2Fe14B, focusing on the role of 4f electron cloud asphericity.

Findings

Decreasing exchange field reduces K1 and K2 values.

Lower exchange fields at grain boundaries may lead to reduced local anisotropy.

The study links exchange field strength to coercivity degradation.

Abstract

To identify the possible mechanism of coercivity (Hc) degradation of Nd-Fe-B sintered magnets, we study the roles of the exchange field acting on the 4f electrons in Nd ions and theoretically investigate how the variation of the exchange field affects the values of the magnetic anisotropy constants K1 and K2. We find that, with decreasing exchange field strength, both values decrease as a result of the lower asphericity of the 4f electron cloud, indicating that the local anisotropy constants might become small around the grain boundaries where the exchange fields are decreased owing to the smaller coordination number.