Sign Reversal of Hall Conductivity in Polycrystalline FeRh Films via the Topological Hall Effect in the Antiferromagnetic Phase.

Abstract

The intrinsic Berry curvature in ferromagnetic (FM) materials significantly influences Hall conductivity during the antiferromagnetic (AFM)-to-FM phase transition, as demonstrated through the anomalous Hall effect (AHE). First-principles calculations indicate negligible spin Hall conductivity in FeRh materials in the AFM phase due to time-reversal symmetry breaking. To date, the contribution of the Berry curvature to the spin Hall effect remains unexamined in the context of AHE measurements. This study presents the temperature-dependent spin and carrier transport properties of FeRh thin films across AFM-to-FM transitions. In the AFM phase, a nonzero AHE signal is observed and even reverses its sign when the film transitions to the FM phase (above <i>T</i> = 175 K). This nonzero AHE signal contrasts with predictions from density functional theory calculations. Notably, an additional Hall conductivity contribution (topological Hall effect), attributed to the spin Berry curvature, results in an overall weak negative Hall conductivity in the AFM phase.