Tailoring the anomalous Hall effect of SrRuO3 thin films by strain: A first principles study

Abstract

Motivated by the recently observed unconventional Hall effect in ultrathin films of ferromagnetic SrRuO3 (SRO), we investigate the effect of strain-induced oxygen octahedral distortion in the electronic structure and anomalous Hall response of the SRO ultrathin films by virtue of density functional theory calculations. Our findings reveal that the ferromagnetic SRO films grown on SrTiO3 (in-plane strain of −0.47%) have an orthorhombic (both tilting and rotation) distorted structure, and with an increasing amount of substrate induced compressive strain the octahedral tilting angle is found to be suppressed gradually, with SRO films grown on NdGaO3 (in-plane strain of −1.7%) stabilized in the tetragonal distorted structure (with zero tilting). Our Berry curvature calculations predict a positive value of the anomalous Hall conductivity of +76 S/cm at −1.7% strain, whereas it is found to be negative (−156 S/cm) at −0.47% strain. We attribute the found behavior of the anomalous Hall effect to the nodal point dynamics in the electronic structure arising in response to tailoring the oxygen octahedral distortion driven by the substrate induced strain. We also calculate strain-mediated anomalous Hall conductivity as a function of reduced magnetization obtained by scaling down the magnitude of the exchange field inside Ru atoms finding good qualitative agreement with experimental observations, which indicates a strong impact of longitudinal thermal fluctuations of Ru spin moments on the anomalous Hall effect in this system.