Magnetic anisotropy of the layered van der Waals antiferromagnet MnSb₂Te₄

Recent discovery of van der Waals (vdW) layered antiferromagnets (AFM) of the Mn(Bi,Sb)₂Te₄ class provides unprecedented opportunities for exploring a richness of magnetic states with non-trivial topology. MnBi₂Te₄ (MBT) is a confirmed topological insulator, known to host quantum anomalous Hall (QAH) state [1]. MnSb₂Te₄ (MST) has the same tetradymite-type crystal structure with the R3m space group as MBT, but by contrast to MBT can have a significant population of Sb_Mn antisite defects and has been surmised to be a type II Weyl semimetal. Here we report on magnetic anisotropy deduced from the detailed angular field-dependence of magnetotransport in AFM MST. Negative magnetoresistance (n-MR) is observed under arbitrary field orientation below and above the Néel temperature T_N ~ 18.5 K, indicating strong spin scattering in both the AFM and paramagnetic states. However, the low-field dependence of n-MR is strikingly different for H||c and H||ab, rapidly decreasing above the characteristic AFM field H₂ ~1.5 T for the former but strictly field-linear for the latter, with the parabolic (∝ B²) positive MR recovered above ~ 6 T. The comparison of magnetic anisotropy obtained from n-MR in MST and MBT and investigated by the DFT calculations will be presented, and the relation to the putative chiral anomaly in MST expected in a Weyl semimetal will be discussed.