Infrared anomalous Hall effect in SrRuO$_3$: Evidence for crossover to intrinsic behavior

TL;DR

This study uses mid-infrared magneto-optical measurements to investigate the anomalous Hall effect in SrRuO$_3$, revealing a crossover from extrinsic to intrinsic behavior around 200 meV energy.

Contribution

First MIR measurements of Hall, Faraday, and Kerr angles in SrRuO$_3$, demonstrating energy-dependent crossover from extrinsic to intrinsic anomalous Hall effect behavior.

Findings

Hall effect sign change below 200 meV with temperature

Above 200 meV, Hall response aligns with intrinsic AHE predictions

Frequency dependence indicates extrinsic effects dominate at lower energies

Abstract

The origin of the Hall effect in many itinerant ferromagnets is still not resolved, with an anomalous contribution from the sample magnetization that can exhibit extrinsic or intrinsic behavior. We report the first mid-infared (MIR) measurements of the complex Hall ($\theta_H$), Faraday ($\theta_F$), and Kerr ($\theta_K$) angles, as well as the Hall conductivity ($\sigma_{xy}$) in a SrRuO$_3$ film in the 115-1400 meV energy range. The magnetic field, temperature, and frequency dependence of the Hall effect is explored. The MIR magneto-optical response shows very strong frequency dependence, including sign changes. Below 200 meV, the MIR $\theta_H (T)$ changes sign between 120 and 150 K, as is observed in dc Hall measurements. Above 200 meV, the temperature dependence of $\theta_H$ is similar to that of the dc magnetization and the measurements are in good agreement with predictions from a band calculation for the intrinsic anomalous Hall effect (AHE). The temperature and frequency dependence of the measured Hall effect suggests that whereas the behavior above 200 meV is consistent with an intrinsic AHE, the extrinsic AHE plays an important role in the lower energy response.