Robust A-Type Order and Spin-Flop Transition on the Surface of the Antiferromagnetic Topological Insulator MnBi2Te4

Here, we present microscopic evidence of the persistence of uniaxial A-type antiferromagnetic order to the surface layers of MnBi2Te4 single crystals using magnetic force microscopy. Our results reveal termination-dependent magnetic contrast across both surface step edges and domain walls, which can be screened by thin layers of soft magnetism. The robust surface A-type order is further corroborated by the observation of termination-dependent surface spin-flop transitions, which have been theoretically proposed decades ago. Our results not only provide key ingredients for understanding the electronic properties of the antiferromagnetic topological insulator MnBi2Te4, but also open a new paradigm for exploring intrinsic surface metamagnetic transitions in natural antiferromagnets.