Spin-flop phase transition in the orthorhombic antiferromagnetic topological semimetal Cu_0.95MnAs

The orthorhombic antiferromagnetic compound CuMnAs was recently predicted to be an antiferromagnetic Dirac semimetal if both the R_y gliding and the S_2z rotational symmetries are preserved in its magnetic ordered state. In our previous work on Cu_0.95MnAs and Cu_0.98Mn_0.96As, we showed that in their low temperature commensurate antiferromagnetic state the b-axis is the magnetic easy axis, breaking the S_2z symmetry and resulting in a polarized surface state that could make this material potentially interesting for antiferromagnetic spintronics. In this paper, we report a detailed study of the anisotropic magnetic properties and magnetoresistance of Cu_0.95MnAs and Cu_0.98Mn_0.96As. Our study shows that in Cu_0.95MnAs the magnetic easy axis is along the b direction and the hard axis is along c. Furthermore, it reveals that Cu_0.95MnAs features a spin-flop phase transition at high temperatures and low fields when the field is applied along the easy b axis. However, no metamagnetic transition is observed for Cu_0.98Mn_0.96As, indicating that the magnetic interactions in this system are very sensitive to Cu vacancies and Cu/Mn site mixing.