Magnetic anisotropy in single-crystalline antiferromagnetic Mn2Au

Abstract

Multiple recent studies have identified the metallic antiferromagnet ${\mathrm{Mn}}_2\mathrm{Au}$ to be a candidate for spintronic applications due to apparent in-plane anisotropy, preserved magnetic properties above room temperature, and current-induced Néel vector switching. Crystal growth is complicated by the fact that ${\mathrm{Mn}}_2\mathrm{Au}$ melts incongruently. We present a bismuth flux method to grow millimeter-scale bulk single crystals of ${\mathrm{Mn}}_2\mathrm{Au}$ in order to examine the intrinsic anisotropic electrical and magnetic properties. Flux quenching experiments reveal that the ${\mathrm{Mn}}_2\mathrm{Au}$ crystals precipitate below $550{}^{\circ }\mathrm{C}$, about $100{}^{\circ }\mathrm{C}$ below the decomposition temperature of ${\mathrm{Mn}}_2\mathrm{Au}$. Bulk ${\mathrm{Mn}}_2\mathrm{Au}$ crystals have a room-temperature resistivity of 16–19 $\mu \mathrm{\Omega }\mathrm{cm}$ and a residual resistivity ratio of 41. ${\mathrm{Mn}}_2\mathrm{Au}$ crystals have a dimensionless susceptibility on the order of ${10}^{-4}$ (SI units), comparable to calculated and experimental reports on powder samples. Single-crystal neutron diffraction confirms the in-plane magnetic structure. The tetragonal symmetry of ${\mathrm{Mn}}_2\mathrm{Au}$ constrains the $ab$-plane magnetic susceptibility to be constant, meaning that ${\chi }_{100}={\chi }_{110}$ in the low-field limit, below any spin-flop transition. We find that three measured magnetic susceptibilities ${\chi }_{100}, {\chi }_{110}$, and ${\chi }_{001}$ are the same order of magnitude and agree with the calculated prediction, meaning the low-field susceptibility of ${\mathrm{Mn}}_2\mathrm{Au}$ is quite isotropic, despite clear differences in $ab$-plane and $ac$-plane magnetocrystalline anisotropy. ${\mathrm{Mn}}_2\mathrm{Au}$ is calculated to have an extremely high in-plane spin-flop field above 30 T, which is much larger than that of another in-plane antiferromagnet, ${\mathrm{Fe}}_2\mathrm{As}$ (less than 1 T). The subtle anisotropy of intrinsic susceptibilities may lead to dominating effects from shape, crystalline texture, strain, and defects in devices that attempt spin readout in ${\mathrm{Mn}}_2\mathrm{Au}$.