Thickness Dependence of Electronic Properties of Topological Antiferromagnet MnBi₂Te₄ Films

The prerequisite for the realization of the quantum anomalous Hall (QAH) state is an interplay between topology and magnetism. More recently, MnBi₂Te₄ was experimentally demonstrated to be a material in which the topological and magnetic states intrinsically coexist. The QAH and axion insulator states were predicted in thin films of MnBi₂Te₄ when the number of layers is odd and even, respectively. Here, we synthesized MnBi₂Te₄ thin films with thicknesses down to one layer using molecular beam epitaxy (MBE) and systematically studied the thickness dependence of electronic properties. Both Hall and Magneto-Optical Kerr Effect measurements show a clear ferromagnetic hysteresis in the one-layer sample. For films thicker than one layer, similar to the exfoliated MnBi₂Te₄ devices, the samples show a small ferromagnetic hysteresis loop at the low magnetic field and spin flop transitions at the high magnetic field. We also found the Hall resistance under zero magnetic field displays an odd/even oscillation, i.e., the samples with odd (even) layers exhibit an anomalous Hall (AH) hysteresis loop with a negative (positive) sign.