Spin-wave dispersion and exchange stiffness in Nd$_2$Fe$_{14}$B and $R$Fe$_{11}$Ti ($R$=Y, Nd, Sm) from first-principles calculations

TL;DR

This study uses first-principles calculations to analyze spin-wave dispersion and exchange stiffness in rare-earth magnets, revealing anisotropic behaviors influenced by exchange interactions.

Contribution

The paper introduces a reciprocal-space algorithm for calculating spin-wave dispersion and provides detailed insights into exchange stiffness anisotropy in Nd-Fe-Ti compounds.

Findings

Exchange stiffness in Nd$_2$Fe$_{14}$B matches experimental ranges.

Short-range exchange couplings cause anisotropy, which is reduced by long-range interactions.

Y, Nd, Sm in $R$Fe$_{11}$Ti exhibit significant anisotropy in exchange stiffness.

Abstract

We theoretically investigate spin-wave dispersion in rare-earth magnet compounds by using first-principles calculations and a method we call the reciprocal-space algorithm (RSA). The value of the calculated exchange stiffness for Nd$_2$Fe$_{14}$B is within the range of reported experimental values. We find that the exchange stiffness is considerably anisotropic when only short-range exchange couplings are considered, whereas inclusion of long-range couplings weakens the anisotropy. In contrast, $R$Fe$_{11}$Ti ($R$=Y, Nd, Sm) shows large anisotropy in the exchange stiffness.