Impact of Lattice Distortions on Magnetocrystalline Anisotropy and Magnetization in (Nd$_{1-x}$Pr$_x$)$_2$Fe$_{14}$B Alloys

TL;DR

This study investigates how lattice distortions affect magnetocrystalline anisotropy and magnetization in (Nd$_{1-x}$Pr$_x$)$_2$Fe$_{14}$B alloys, revealing significant strain-induced changes crucial for magnetic material design.

Contribution

It provides the first detailed computational analysis of strain effects on magnetic anisotropy in Nd-Pr-Fe-B alloys, linking microscopic lattice distortions to magnetic properties.

Findings

Compressive strain up to 25% can invert the sign of $K_{u}$.

Pr-rich alloys show greater reduction in $K_{u}$ under strain.

Strain-dependent parameters inform future micromagnetic simulations.

Abstract

Nd$_{2}$Fe$_{14}$B -- a widely used permanent magnet -- has magnetocrystalline anisotropy constants that differ between the bulk and interface regions. This study explores the effects of lattice distortion on the magnetocrystalline anisotropy ($K_{\rm u}$) and magnetization of (Nd$_{1-x}$Pr$_x$)$_2$Fe$_{14}$B. Nd$_2$Fe$_{14}$B alloys were fabricated; scanning transmission electron microscopy revealed a compressive strain of up to 25% near grain boundaries. Using the full-potential Korringa--Kohn--Rostoker method, we calculated the strain dependence of $K_{\rm u}$, showing that although $K_{\rm u}$ is 4.2 MJ/m$^3$ under strain-free conditions at 0 K, it becomes negative in regions with 25% compressive strain. Additionally, Pr$_{2}$Fe$_{14}$B exhibits a larger $K_{\rm u}$ than Pr$_{2}$Fe$_{14}$B under undistorted conditions, whereas Pr-rich alloys exhibit a more pronounced reduction in $K_{\rm u}$ under strain. These findings highlight the critical influence of lattice distortions on magnetic properties. The calculated strain-dependent magnetic anisotropy parameters provide valuable inputs for future micromagnetic simulations, aiding the design of advanced magnetic materials.