Isotropic orbital magnetic moments in magnetically anisotropic SrRuO3 films

TL;DR

This study reveals that in epitaxially strained SrRuO3 films, the orbital magnetic moments are isotropic and contribute negligibly to magnetic anisotropy, challenging existing theoretical models.

Contribution

It provides the first detailed element-specific analysis showing isotropic orbital magnetic moments in strained SrRuO3 films, contradicting Bruno's model.

Findings

Orbital magnetic moments are isotropic despite magnetic anisotropy.

Strong magnetic coupling between Ru 4d and O 2p ions.

Orbital magnetic moments have negligible contribution to magnetic anisotropy.

Abstract

Epitaxially strained SrRuO3 films have been a model system for understanding the magnetic anisotropy in metallic oxides. In this paper, we investigate the anisotropy of the Ru 4d and O 2p electronic structure and magnetic properties using high-quality epitaxially strained (compressive and tensile) SrRuO3 films grown by machine-learning-assisted molecular beam epitaxy. The element-specific magnetic properties and the hybridization between the Ru 4d and O 2p orbitals were characterized by Ru M2,3-edge and O K-edge soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements. The magnetization curves for the Ru 4d and O 2p magnetic moments are identical, irrespective of the strain type, indicating the strong magnetic coupling between the Ru and O ions. The electronic structure and the orbital magnetic moment relative to the spin magnetic moment are isotropic despite the perpendicular and in-plane magnetic anisotropy in the compressive-strained and tensile-strained SrRuO3 films; i.e., the orbital magnetic moments have a negligibly small contribution to the magnetic anisotropy. This result contradicts Bruno model, where magnetic anisotropy arises from the difference in the orbital magnetic moment between the perpendicular and in-plane directions. Contributions of strain-induced electric quadrupole moments to the magnetic anisotropy are discussed, too.