Spin orientation and magnetostriction of Tb$_{1-x}$Dy$_{x}$Fe$_{2}$ from first principles

TL;DR

This study uses first-principles calculations to determine the optimal dysprosium concentration in Tb$_{1-x}$Dy$_x$Fe$_2$ for maximum magnetostriction at room temperature, aligning well with experimental data.

Contribution

The paper introduces a first-principles approach to predict the optimal composition and magnetostrictive properties of Tb-Dy-Fe compounds, providing insights into their magnetic behavior.

Findings

Critical Dy concentration for magnetization switch: x_c=0.78

Calculated magnetostrictions: λ_{111}=2700 ppm, λ_{100}=-430 ppm

Optimal composition near x=0.73 for room temperature applications

Abstract

The optimal amount of dysprosium in the highly magnetostrictive rare-earth compounds Tb$_{1-x}$Dy$_x$Fe$_2$ for room temperature applications has long been known to be $x$=0.73 (Terfenol-D). Here, we derive this value from first principles by calculating the easy magnetization direction and magnetostriction as a function of composition and temperature. We use crystal field coefficients obtained within density-functional theory to construct phenomenological anisotropy and magnetoelastic constants. The temperature dependence of these constants is obtained from disordered local moment calculations of the rare earth magnetic order parameter. Our calculations find the critical Dy concentration required to switch the magnetization direction at room temperature to be $x_c$=0.78, with magnetostrictions $\lambda_{111}$=2700 and $\lambda_{100}$=-430~ppm, close to the Terfenol-D values.