C-type antiferromagnetic structure of topological semimetal CaMnSb_2

Determination of the magnetic structure and confirmation of the presence or absence of inversion (𝒫) and time reversal (𝒯) symmetry is imperative for correctly understanding the topological magnetic materials. Here high-quality single crystals of the layered manganese pnictide CaMnSb_2 are synthesized using the self-flux method. De Haas-van Alphen oscillations indicate a nontrivial Berry phase of ∼ π and a notably small cyclotron effective mass, supporting the Dirac semimetal nature of CaMnSb_2. Neutron diffraction measurements identify a C-type antiferromagnetic (AFM) structure below T_N = 303(1) K with the Mn moments aligned along the a axis, which is well supported by the density functional theory (DFT) calculations. The corresponding magnetic space group is Pn'm'a', preserving a 𝒫×𝒯 symmetry. Adopting the experimentally determined magnetic structure, band crossings near the Y point in momentum space and linear dispersions of the Sb 5p_y,z bands are revealed by the DFT calculations. Furthermore, our study predicts the possible existence of an intrinsic second-order nonlinear Hall effect in CaMnSb_2, offering a promising platform to study the impact of topological properties on nonlinear electrical transports in antiferromagnets.