Interface-driven unusual anomalous Hall effect in M nxGa/Pt bilayers

The effects of spin-orbit coupling and symmetry breaking at the interface between a ferromagnet and heavy metal are particularly important for spin-based information storage and computation. Recent discoveries suggest they can create novel chiral spin structures (e.g., skyrmions), which have often been identified through the appearance of the bump/dip features of Hall signals, the so-called topological Hall effect (THE). In this work, however, we present an unusual anomalous Hall effect (UAHE) in MnxGa/Pt bilayers and demonstrate that the features extremely similar to THE can be generated without involving any chiral spin structures. Low-temperature magnetic force microscopy has been used to explore the magnetic field-dependent behavior of spin structures, and the UAHE as a function of magnetic field does not peak near the maximal density of magnetic bubbles. Our results unambiguously evidence that the UAHE in MnxGa/Pt bilayers shows no correlation with chiral spin structures but is driven by the modified interfacial properties, indicating a wealth of underlying and interesting physics.