Intrinsic magnetic properties of {$R$(Fe$_{1-x}$Co$_{x}$)$_{11}$Ti$Z$} ($R$ = Y and Ce; $Z$ = H, C, and N)

TL;DR

This study uses density functional theory to analyze the intrinsic magnetic properties of $R$(Fe$_{1-x}$Co$_{x}$)$_{11}$Ti$Z$ compounds, revealing complex behaviors influenced by composition, site contributions, and interstitial doping.

Contribution

It provides detailed theoretical insights into how composition and doping affect magnetic properties, aiding the design of better permanent magnets with reduced critical materials.

Findings

Magnetization, Curie temperature, and anisotropy energy agree with experiments.

All Fe sublattices promote uniaxial anisotropy in YFe$_{11}$Ti.

Interstitial doping enhances Curie temperature, with N being most effective.

Abstract

To guide improved properties coincident with reduction of critical materials in permanent magnets, we investigate via density functional theory (DFT) the intrinsic magnetic properties of a promising system, $R$(Fe$_{1-x}$Co$_{x}$)$_{11}$Ti$Z$ with $R$=Y, Ce and interstitial doping ($Z$=H, C, N). The magnetization $M$, Curie temperature $T_\text{C}$, and magnetocrystalline anisotropy energy $K$ calculated in local density approximation to DFT agree well with measurements. Site-resolved contributions to $K$ reveal that all three Fe sublattices promote uniaxial anisotropy in YFe$_{11}$Ti, while competing anisotropy contributions exist in YCo$_{11}$Ti. As observed in experiments on $R$(Fe$_{1-x}$Co$_{x}$)$_{11}$Ti, we find a complex nonmonotonic dependence of $K$ on Co content, and show that anisotropy variations are a collective effect of MAE contributions from all sites and cannot be solely explained by preferential site occupancy. With interstitial doping, calculated $T_\text{C}$ enhancements are in the sequence of N$>$C$>$H, with volume and chemical effects contributing to the enhancement. The uniaxial anisotropy of $R$(Fe$_{1-x}$Co$_{x}$)$_{11}$Ti$Z$ generally decreases with C and N; although, for $R$=Ce, C doping is found to greatly enhance it for a small range of 0.7$<$$x$$<$0.9.