Layer-Dependent Magnetic Structure and Anomalous Hall Effect in the Magnetic Topological Insulator MnBi 4 Te 7 .

The intrinsic antiferromagnetic topological insulator (TI) MnBi 4 Te 7 provides a capacious playground for the realization of topological quantum phenomena, such as the axion insulator states and quantum anomalous Hall (QAH) effect. In addition to nontrivial band topology, magnetism is another necessary ingredient for realizing these quantum phenomena. Here, we investigate signatures of thickness-dependent magnetism in exfoliated MnBi 4 Te 7 thin flakes. We observe an obvious odd-even layer-number effect in few-layer MnBi 4 Te 7 . Noticeably, we show that in monolayer MnBi 4 Te 7 the anomalous Hall effect exhibits a sign reversal. Compared with the case of MnBi 2 Te 4 , interlayer antiferromagnetic exchange coupling, which is essential for the realization of the QAH effect, is greatly suppressed in MnBi 4 Te 7 . The demonstration of thickness-dependent magnetic properties is helpful to further explore the topological quantum phenomena in MnBi 4 Te 7 .