Ferromagnetic-antiferromagnetic coexisting ground state and exchange bias effects in MnBi4Te7 and MnBi6Te10

Natural superlattice structures MnBi2Te4(Bi2Te3)(n) (n=1, 2, ...), in which magnetic MnBi2Te4 layers are separated by nonmagnetic Bi2Te3 layers, hold band topology, magnetism and reduced interlayer coupling, providing a promising platform for the realization of exotic topological quantum states. However, their magnetism in the two-dimensional limit, which is crucial for further exploration of quantum phenomena, remains elusive. Here, complex ferromagnetic-antiferromagnetic coexisting ground states that persist down to the 2-septuple layers limit are observed and comprehensively investigated in MnBi4Te7 (n=1) and MnBi6Te10 (n=2). The ubiquitous Mn-Bi site mixing modifies or even changes the sign of the subtle interlayer magnetic interactions, yielding a spatially inhomogeneous interlayer coupling. Further, a tunable exchange bias effect, arising from the coupling between the ferromagnetic and antiferromagnetic components in the ground state, is observed in MnBi2Te4(Bi2Te3)(n) (n=1, 2), which provides design principles and material platforms for future spintronic devices. Our work highlights a new approach toward the fine-tuning of magnetism and paves the way for further study of quantum phenomena in MnBi2Te4(Bi2Te3)(n) (n=1, 2) as well as their magnetic applications. MnBi2Te4 and Bi2Te3 can form natural superlattices, where the MnBi2Te4 layers are separated by multiples of Bi2Te3. The combination of these two materials offers a potential platform for the interplay of tunable magnetism and topology. Here, the authors show that MnBi4Te7 and MnBi6Te10 display a complex magnetic ground state with coexisting ferromagnetic and antiferromagnetic domains.

Automated summary

Natural superlattices MnBi2Te4(Bi2Te3)(n) (n=1, 2, ...) with band topology and reduced interlayer coupling provide a promising platform for exploring topological quantum states. In this study, the authors observe and investigate complex ferromagnetic-antiferromagnetic coexisting ground states in MnBi4Te7 (n=1) and MnBi6Te10 (n=2). The spatially inhomogeneous interlayer coupling and tunable exchange bias effect have been observed in MnBi2Te4(Bi2Te3)(n) (n=1, 2), providing design principles for future spintronic devices.