Exchange bias and anomalous Hall effect driven by intertwined magnetic phases in MnBi 4 Te 7

We report on the interplay between atomic-scale inhomogeneity and competing magnetic phases and their effect on the anomalous Hall effect in the layered antiferromagnet ${\mathrm{MnBi}}₄{\mathrm{Te}}₇$, a natural superlattice hosting coexisting ferromagnetic and antiferromagnetic phases. Using a combination of scanning tunneling microscopy (STM), DC and AC magnetization, and magnetotransport 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 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 $\ensuremath{-}264$ to $+306$ Oe. This sign reversal indicates a field-induced change in interfacial coupling. The temperature dependence of longitudinal resistivity (${\ensuremath{\rho}}_xx$) 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.