Intrinsic low-spin state and strain-tunable anomalous Hall scaling in high-quality SrRuO3 (111) films

Abstract

The (111)-oriented 4d ferromagnetic perovskite SrRuO3 (SRO) offers a unique triangular-lattice geometry, making it a promising platform for exploring Berry-curvature-driven and spin-orbit-coupled transport. Here, we present a systematic study of the structure, magnetism, and magnetotransport of high-quality SRO (111) thin films with thicknesses t = 1.2-60 nm grown on SrTiO3 (111) substrates by machine-learning-assisted molecular beam epitaxy. We achieved a residual resistivity ratio of 45.5 in a 60 nm-thick film, the highest reported for this orientation, enabling access to intrinsic electronic and magnetic behavior. Temperature-dependent resistivity confirms Fermi-liquid transport below 15 K in both coherently strained (t = 10, 20 nm) and strain-relaxed (t = 60 nm) films, thereby enabling detailed magnetotransport and magnetic measurements. The linear, non-saturating positive magnetoresistance persists up to 14 T, while Hall-effect measurements and temperature scaling separate intrinsic (Karplus-Luttinger) and extrinsic (side-jump) contributions to the anomalous Hall effect, with the relative weight tuned by (111) epitaxial strain. X-ray magnetic circular dichroism at the Ru M2,3 and O K edges, together with SQUID magnetometry, demonstrates an intrinsically low-spin Ru ground state for both coherently strained and relaxed films, resolving ambiguities among prior reports. These detailed crystalline, electrical, and magnetic characterizations provide a rigorous foundation for understanding and engineering quantum transport in SRO (111).