Tailoring Néel Orders in Layered Topological Antiferromagnet MnBi_{2}Te_{4}.

In the two-dimensional limit, the interplay between Néel order and band topology in van der Waals topological antiferromagnets can give rise to novel quantum phenomena in the quantum anomalous Hall state. However, because of the absence of net magnetization in antiferromagnets, probing the energetically degenerate Néel orders has long remained a significant challenge. In this Letter, we demonstrate deterministic control over the Néel orders in MnBi_{2}Te_{4} thin flakes through surface anisotropy engineering enabled by the AlO_{x} capping layer. By tuning the surface anisotropy, we uncover parity-dependent symmetry breaking states that manifest as distinct odd-even boundary architectures, including 180° domain walls or continuous spin structures. Comparative studies between AlO_{x}-capped and pristine odd-layer MnBi_{2}Te_{4} flakes using domain-resolved magnetic force microscopy reveal pronounced differences in coercivity and magnetization-reversal dynamics. Notably, an unconventional giant exchange bias, which arises from perpendicular magnetic anisotropy, has been discovered. Our findings establish a pathway for manipulating Néel order through surface modification in topological antiferromagnets.