Polar magneto-optical Kerr effect from antiferromagnetic M₂As (M=Cr, Mn, and Fe) under external magnetic field

Polar magneto-optical Kerr effect (PMOKE) is a great tool to detect ferromagnetic domains and their magnetization but is of no use for antiferromagnets without external magnetic field. To understand PMOKE from antiferromagnets under external magnetic field, we use first-principles density functional theory. Due to the lack of net magnetization in the ground state, spin tilting is only induced by an external field, leading symmetry breaking and thus PMOKE signal arises. Based on band structure analysis, exchange splitting and spin-orbit coupling effects are confirmed, similar to ferromagnetic materials. While the spin-orbit coupling is affected little by the external field, exchange splitting arises due to spin tilting. Majority and minority spin states are increasingly separated as external magnetic field increases. Furthermore, in antiferromagnets magnetic susceptibility is related to spin tilting. We compute the magnetic susceptibility of Cr₂As, Mn₂As, and Fe₂As and find that Fe₂As presents largest PMOKE signal at a given external magnetic field as well as the largest susceptibility. Large susceptibility leads to larger spin tilting and, hence, more exchange splitting and stronger PMOKE signal.