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

Antiferromagnetic (AFM) metals have attracted tremendous interest for memory applications due to their expected fast response dynamics in the terahertz frequency regime. Spin dynamics such as AFM resonance and the magnon relaxation rate have been measured using the linear magneto-optical Kerr effect (MOKE) with coherent spin precession induced by laser pumping. Polarized electromagnetic radiation is a promising alternative for probing the response in canted AFM systems. Hence, in this paper, we use first-principles simulations to study the magneto-optical response of AFM ${M}₂\mathrm{As} (M=\mathrm{Cr},\mathrm{Mn},\text{and} \mathrm{Fe})$ under external magnetic fields. We devise a computational scheme to compute the magnetic susceptibility from total-energy changes using constraints on magnetic-moment tilting. Our predictions of the spectral dependence of polar magneto-optical Kerr rotation and ellipticity allow us to attribute these effects to breaking of the magnetic symmetry. We show that tilting of magnetic moments affects the exchange interaction, while the spin-orbit interaction remains unaffected. In this paper, we provide an understanding of the polar MOKE on a band structure level and underscore the importance of the magnetic susceptibility when searching for materials with large magneto-optical response.