Biaxial Strain Control of Helimagnetism via Chemical Expansion in Thin Film SrFeO3

TL;DR

This study shows how biaxial strain in SrFeO3 thin films can control helimagnetic order by inducing chemical expansion, which affects magnetic interactions through defect and lattice modifications.

Contribution

It introduces chemical expansion as a novel mechanism to tune helimagnetism in oxide thin films via epitaxial strain effects.

Findings

Tensile strain shortens helimagnetic ordering length

Strain tilts magnetic ordering vector

Chemical expansion modifies Fe-O hybridization

Abstract

We demonstrate control of helimagnetic order in biaxially strained SrFeO3 thin films using neutron diffraction and resonant soft x-ray scattering. SrFeO3, a negative charge-transfer oxide, exhibits a complex magnetic phase diagram that includes multi-q spin structures. Tensile epitaxial strain produces a pronounced shortening of the helimagnetic ordering length and a tilting of the magnetic ordering vector. We interpret this behavior in terms of chemical expansion: lattice dilation under tensile strain lowers the energetic cost of oxygen vacancies, leading to an expanded unit cell that modifies Fe-O hybridization and enhances superexchange relative to double exchange. These results reveal how epitaxial strain can indirectly tune helimagnetism through defect-driven chemical expansion, highlighting the strong coupling between lattice, chemistry, and magnetic order in transition-metal oxides. Our findings establish chemical expansion as an effective mechanism for engineering complex magnetic textures in oxide thin films, with implications for spintronic, magnonic, and quantum information applications.