Metallicity and Anomalous Hall Effect in Epitaxially-Strained, Atomically-thin RuO2 Films

TL;DR

This study demonstrates that ultrathin epitaxially-strained RuO2 films exhibit a sizeable anomalous Hall effect at lower magnetic fields, revealing strain-induced magnetic properties and potential for spintronic applications.

Contribution

The paper reports the first observation of AHE in ultrathin, fully-strained RuO2 films, showing strain stabilizes magnetic order and enables lower-field AHE detection.

Findings

Ultrathin RuO2 films retain metallicity under strain.

Strain stabilizes a non-compensated magnetic ground state.

AHE observed at magnetic fields below 9 T.

Abstract

The anomalous Hall effect (AHE), a hallmark of time-reversal symmetry breaking, has been reported in rutile RuO2, a debated metallic altermagnetic candidate. Previously, AHE in RuO2 was observed only in strain-relaxed thick films under extremely high magnetic fields (~50 T). Yet, in ultrathin strained films with distinctive anisotropic electronic structures, there are no reports, likely due to disorder and defects suppressing metallicity thus hindering its detection. Here, we demonstrate that ultrathin, fully-strained 2 nm TiO2/t nm RuO2/TiO2 (110) heterostructures, grown by hybrid molecular beam epitaxy, retain metallicity and exhibit a sizeable AHE at a significantly lower magnetic field (< 9 T). Density functional theory calculations reveal that epitaxial strain stabilizes a non-compensated magnetic ground state and reconfigures magnetic ordering in RuO2 (110) thin films. These findings establish ultrathin RuO2 as a platform for strain-engineered magnetism and underscore the transformative potential of epitaxial design in advancing spintronic technologies.