C-Type Antiferromagnetic Structure of Topological Semimetal CaMnSb₂

Determination of the magnetic structure and confirmation of the presence or absence of inversion ($\mathcal{P}$) and time reversal ($\mathcal{T}$) symmetry is imperative for correctly understanding the topological magnetic materials. Here high-quality single crystals of the layered manganese pnictide CaMnSb₂ 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 CaMnSb₂. Neutron diffraction measurements identify a C-type antiferromagnetic 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 $\mathcal{P}\times \mathcal{T}$ 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 CaMnSb₂, offering a promising platform to study the impact of topological properties on nonlinear electrical transports in antiferromagnets.