Magnetic anisotropy in single-crystalline antiferromagnetic Mn2Au

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 N\'eel 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 $550{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, about $100{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ 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 $\textmu{}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$ and a residual resistivity ratio of 41. ${\mathrm{Mn}}_{2}\mathrm{Au}$ crystals have a dimensionless susceptibility on the order of ${10}^{\ensuremath{-}4}$ (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 ${\ensuremath{\chi}}_{100}={\ensuremath{\chi}}_{110}$ in the low-field limit, below any spin-flop transition. We find that three measured magnetic susceptibilities ${\ensuremath{\chi}}_{100}, {\ensuremath{\chi}}_{110}$, and ${\ensuremath{\chi}}_{001}$ 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 ${\mathrm{Mn}}_{2}\mathrm{Au}$.