Anomalous and topological Hall effects in epitaxial thin films of the noncollinear antiferromagnet Mn$_{3}$Sn

TL;DR

This study reports the successful growth of epitaxial Mn$_{3}$Sn thin films exhibiting anomalous and topological Hall effects, linked to their noncollinear antiferromagnetic structure and Berry curvature effects, with controllable topological Hall signatures.

Contribution

First demonstration of epitaxial Mn$_{3}$Sn thin films showing both anomalous and topological Hall effects linked to their magnetic structure.

Findings

Epitaxial growth of Mn$_{3}$Sn films with specific orientations.

Observation of large anomalous Hall effect at room temperature.

Detection of topological Hall effect related to scalar spin chirality at low temperatures.

Abstract

Noncollinear antiferromagnets with a D0$_{19}$ (space group = 194, P6$_{3}$/mmc) hexagonal structure have garnered much attention for their potential applications in topological spintronics. Here, we report the deposition of continuous epitaxial thin films of such a material, Mn$_{3}$Sn, and characterize their crystal structure using a combination of x-ray diffraction and transmission electron microscopy. Growth of Mn$_{3}$Sn films with both (0001) c-axis orientation and (40$\bar{4}$3) texture is achieved. In the latter case, the thin films exhibit a small uncompensated Mn moment in the basal plane, quantified via magnetometry and x-ray magnetic circular dichroism experiments. This cannot account for the large anomalous Hall effect simultaneously observed in these films, even at room temperature, with magnitude $\sigma_{\mathrm{xy}}$ ($\mu_{0}H$ = 0 T) = 21 $\mathrm{\Omega}^{-1}\mathrm{cm}^{-1}$ and coercive field $\mu_{0}H_{\mathrm{C}}$ = 1.3 T. We attribute the origin of this anomalous Hall effect to momentum-space Berry curvature arising from the symmetry-breaking inverse triangular spin structure of Mn$_{3}$Sn. Upon cooling through the transition to a glassy ferromagnetic state at around 50 K, a peak in the Hall resistivity close to the coercive field indicates the onset of a topological Hall effect contribution, due to the emergence of a scalar spin chirality generating a real-space Berry phase. We demonstrate that the polarity of this topological Hall effect, and hence the chiral-nature of the noncoplanar magnetic structure driving it, can be controlled using different field cooling conditions.