Inhomogeneous ferromagnetism mimics signatures of the topological Hall effect in SrRuO$_3$ films

TL;DR

This study shows that inhomogeneous ferromagnetism in SrRuO₃ films can produce Hall effect signatures similar to the topological Hall effect, challenging previous interpretations of topological spin textures in similar materials.

Contribution

It demonstrates that Hall effect anomalies attributed to topological textures can arise from ferromagnetic inhomogeneities caused by Ru vacancies, highlighting the need for more direct probes.

Findings

Hall anomalies mimic topological Hall effect signatures

Inhomogeneities in magnetization caused by Ru vacancies explain the anomalies

Results question the identification of topological textures in prior studies

Abstract

Topological transport phenomena in magnetic materials are a major topic of current condensed matter research. One of the most widely studied phenomena is the ``topological Hall effect'' (THE), which is generated via spin-orbit interactions between conduction electrons and topological spin textures such as skyrmions. We report a comprehensive set of Hall effect and magnetization measurements on epitaxial films of the prototypical ferromagnetic metal SrRuO$_3$ the magnetic and transport properties of which were systematically modulated by varying the concentration of Ru vacancies. We observe Hall effect anomalies that closely resemble signatures of the THE, but a quantitative analysis demonstrates that they result from inhomogeneities in the ferromagnetic magnetization caused by a non-random distribution of Ru vacancies. As such inhomogeneities are difficult to avoid and are rarely characterized independently, our results call into question the identification of topological spin textures in numerous prior transport studies of quantum materials, heterostructures, and devices. Firm conclusions regarding the presence of such textures must meet stringent conditions such as probes that couple directly to the non-collinear magnetization on the atomic scale.