Superexchange Interactions and Magnetic Anisotropy in MnPSe₃ Monolayer

Two-dimensional van der Waals magnetic materials are of great current interest for their promising applications in spintronics. Using density functional theory calculations in combination with the maximally localized Wannier functions method and the magnetic anisotropy analyses, we study the electronic and magnetic properties of MnPSe₃ monolayer. Our results show that it is a charge transfer antiferromagnetic (AF) insulator. For this Mn²⁺ 3d⁵ system, although it seems straightforward to explain the AF ground state using the direct exchange, we find that the nearly 90° Mn–Se–Mn charge transfer type superexchange plays a dominant role in stabilizing the AF ground state. Moreover, our results indicate that, although the shape anisotropy favors an out-of-plane spin orientation, the spin-orbit coupling (SOC) leads to the experimentally observed in-plane spin orientation. We prove that the actual dominant contribution to the magnetic anisotropy comes from the second-order perturbation of the SOC, by analyzing its distribution over the reciprocal space. Using the AF exchange and anisotropy parameters obtained from our calculations, our Monte Carlo simulations give the Néel temperature T_N = 47 K for MnPSe₃ monolayer, which agrees with the experimental 40 K. Furthermore, our calculations show that under a uniaxial tensile (compressive) strain, Néel vector would be parallel (perpendicular) to the strain direction, which well reproduces the recent experiments. We also predict that T_N would be increased by a compressive strain.