Intertwined magnetic phase driven exchange bias and its impact on the anomalous Hall effect in MnBi$_4$Te$_7$

TL;DR

This study investigates how atomic-scale inhomogeneity and competing magnetic phases in MnBi4Te7 influence the anomalous Hall effect, revealing temperature-dependent exchange bias behavior linked to microscopic disorder and interfacial magnetism.

Contribution

It demonstrates the role of intrinsic antisite defects in inducing exchange bias and elucidates the temperature-driven reconfiguration of interfacial spin structures affecting electronic transport.

Findings

Intrinsic Mn Bi antisite defects induce strong interlayer exchange coupling.

Exchange bias transitions from asymmetric to symmetric between 2 K and 6 K.

Coexistence of two distinct spin states near the magnetic transition temperature.

Abstract

We report on the interplay between atomic scale inhomogeneity and competing magnetic phases and its effect on the anomalous Hall effect in the layered antiferromagnet MnBi$_4$Te$_7$, a natural superlattice hosting coexisting ferromagnetic and antiferromagnetic phases. Using a combination of scanning tunneling microscopy (STM), DC and AC magnetization, and magneto-transport measurements, we reveal that intrinsic Mn Bi antisite defects induce strong interlayer exchange coupling, giving rise to a robust exchange bias observed in both magnetic and Hall responses. The exchange bias undergoes a transition from asymmetric to symmetric behavior between 2 K and 6 K, indicating a temperature driven dynamical reconfiguration of interfacial spin structures. The training effect analysis revealed a stronger contribution of frozen spins at 2 K compared to 6 K, with relaxation amplitude shift from -264 Oe to 306 Oe. This sign reversal indicates a field-induced change in interfacial coupling. The temperature dependence of longitudinal resistivity and magnetization reveals complementary behavior, indicating the coexistence of two distinct spin states near the magnetic transition temperature. The phase fraction based resistivity model captures the distinct scattering mechanisms that govern electronic transport across different magnetic regimes. Our findings offer a direct link between microscopic disorder, interfacial magnetism and macroscopic topological phenomena in magnetic topological insulators.