Strain Healing of Spin-Orbit Coupling: A Cause for Enhanced Magnetic Moment in Epitaxial SrRuO3 Thin Films

TL;DR

This study reveals that strain-induced relaxation of orbital quenching, rather than high spin states, enhances the magnetic moment in epitaxial SrRuO3 thin films through strong spin-orbit coupling effects.

Contribution

It demonstrates that strain engineering can relax orbital quenching and enhance magnetic moments via spin-orbit coupling, challenging previous high spin state assumptions.

Findings

Magnetic moment of 3.3 Bohr-magnetron/Ru ion in thin films

Ru ions are in low spin state, not high spin as previously thought

Strong spin-orbit coupling confirmed by x-ray spectroscopy

Abstract

Enhanced magnetic moment and coercivity in SrRuO3 thin films are significant issues for advanced technological usages and hence are researched extensively in recent times. Most of the previous reports on thin films with enhanced magnetic moment attributed the high spin state for the enhancement. Our magnetization results show high magnetic moment of 3.3 Bohr-magnetron/Ru ion in the epitaxial thin films grown on LSAT substrate against 1.2 Bohr-magnetron/Ru ion observed in bulk compound. Contrary to the expectation the Ru ions are found to be in low spin state and the orbital moment is shown to be contributing significantly in the enhancement of magnetic moment. We employed x-ray absorption spectroscopy and resonant valance band spectroscopy to probe the spin state and orbital contributions in these films. The existence of strong spin-orbit coupling responsible for the de-quenching of the 4d orbitals is confirmed by the observation of the non-statistical large branching ratio at the Ru M2,3 absorption edges. The relaxation of orbital quenching by strain engineering provides a new tool for enhancing magnetic moment. Strain disorder is shown to be an efficient mean to control the spin-orbit coupling.