Electric Field-Controlled Magneto-Optical Kerr Effect in A‑Type Antiferromagnetic Fe₂CX₂ (X = F, Cl) and Its Janus Monolayer

The magneto-optical Kerr effect (MOKE) is a powerful probe of magnetism and has recently gained new attention in antiferromagnetic (AFM) materials. Through extensive first-principles calculations and group theory analysis, we have identified Fe₂CX₂ (X = F, Cl) and Janus Fe₂CFCl monolayers as ideal A-type collinear AFM materials with high magnetic anisotropy and Néel temperatures. By applying a vertical external electrical field (E_f) of 0.2 V/Å, the MOKE is activated for Fe₂CF₂ and Fe₂CCl₂ monolayers without changing their magnetic ground state, and the maximum Kerr rotation angles are 0.13 and 0.08°, respectively. Due to the out-of-plane spontaneous polarization, the intrinsic and nonvolatile MOKE is found in the Janus Fe₂CFCl monolayer and the maximal Kerr rotation angle without external electronic field is 0.25°. Moreover, the intrinsic built-in electronic field also gives origin to more robust A-type AFM ordering and reversible Kerr angle against external E_f. Our study suggests that E_f is an effective tool for controlling MOKE in two-dimensional (2D) AFM materials. This research opens the possibility of related studies and applications in AFM spintronics.