Abstract
Here, we report the investigation of the anomalous Hall effect in the magnetically doped topological insulator . We find it contains two contributions of opposite sign. Both components are found to depend differently on carrier density, leading to a sign inversion of the total anomalous Hall effect as a function of applied gate voltage. The two contributions are found to have different magnetization reversal fields, which in combination with a temperature dependent study points towards the coexistence of two ferromagnetic orders in the system. Moreover, we find that the sign of total anomalous Hall response of the system depends on the thickness and magnetic doping density of the magnetic layer. The thickness dependence suggests that the two ferromagnetic components originate from the surface and bulk of the magnetic topological insulator film. We believe that our observations provide insight into the magnetic behavior, and thus will contribute to an eventual understanding of the origin of magnetism in this material class. In addition, our data bear a striking resemblance to anomalous Hall signals often associated with skyrmion contributions. Our analysis provides a straightforward explanation for both the magnetic field dependence of the Hall signal and the observed change in sign without needing to invoke skyrmions, and thus suggest that caution is needed when making claims of effects from skyrmion phases.
- Received 20 August 2019
- Revised 20 November 2019
DOI:https://doi.org/10.1103/PhysRevX.10.011012
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
The Hall effect, where a voltage is induced perpendicular to an electric current and an applied magnetic field, has intrigued physicists for more than a century. The last few decades have witnessed the appearance of its quantum-mechanical cousins, revolutionizing solid-state physics. The most recently discovered Hall family member is the quantum anomalous Hall effect, which stems from the interplay between magnetism and topology. Here, we reveal that one well-studied quantum anomalous Hall system contains two coexisting ferromagnetic states.
The prototypical quantum anomalous Hall material system V-doped (or Cr-doped) has long exhibited hints of a novel complex magnetic state, the mechanism of which has remained an open question. In our work, we add a valuable piece to that puzzle. By examining a broad range of parameters such as magnetic field, temperature, gate voltage, film thickness, and magnetic-doping-level dependence, we find the coexistence of two ferromagnetic orders in , one stemming from the bulk of the material and one associated with the surface of the magnetic topological insulator film.
Significantly, our results provide a clear and simple Occam’s razor description of transport phenomenology in these materials, which argues against the recent esoteric suggestions that skyrmion spin textures—whirls in the material’s magnetism—have been observed in the Hall effect of these materials. Our work therefore implies that great care must be taken when making claims of novel topological skyrmion physics.