Magnetic anisotropy in single-crystalline antiferromagnetic Mn_2Au

Multiple recent studies have identified the metallic antiferromagnet Mn_2Au 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 Mn_2Au melts incongruently. We present a bismuth flux method to grow millimeter-scale bulk single crystals of Mn_2Au in order to examine the intrinsic anisotropic electrical and magnetic properties. Flux quenching experiments reveal that the Mn_2Au crystals precipitate below 550C, about 100C below the decomposition temperature of Mn_2Au. Bulk Mn_2Au crystals have a room-temperature resistivity of 16-19 μΩ-cm and a residual resistivity ratio of 41. Mn_2Au crystals have a dimensionless susceptibility on the order of 10^-4, comparable to calculated and experimental reports on powder samples. Single-crystal neutron diffraction confirms the in-plane magnetic structure. The tetragonal symmetry of Mn_2Au constrains the ab-plane magnetic susceptibility to be constant, meaning that χ_100=χ_110 in the low-field limit, below any spin-flop transition. We find that three measured magnetic susceptibilities χ_100, χ_110, and χ_001 are the same order of magnitude and agree with the calculated prediction, meaning the low-field susceptibility of Mn_2Au is quite isotropic, despite clear differences in ab-plane and ac-plane magnetocrystalline anisotropy. Mn_2Au 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 Fe_2As (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 Mn_2Au.