Epitaxial strain may break the orbital degeneracy, favoring a particular orbital filling. This may influence the magnetic properties of transition metal oxides. Herein, we report the consecutive magnetic order and magnetic anisotropy transitions in $\mathrm{SrM}{\mathrm{n}}_{0.3}{\mathrm{Ir}}_{0.7}{\mathrm{O}}_3$ (SMIO) thin films, with both $3d$ and $5d$ elements on perovskite B sites, as a function of the epitaxial strain. The SMIO films have been epitaxially deposited by pulsed laser deposition on (001)-oriented ${\left({\mathrm{LaAlO}}_3\right)}_{0.3}-{\left({\mathrm{Sr}}_2{\mathrm{AlTaO}}_6\right)}_{0.7}$ substrates buffered with ${\mathrm{BaTiO}}_3$ (BTO) of varying thicknesses. The lattice of the BTO buffer layer relaxes as its thickness increases from 2 to 25 unit cells. Accordingly, the SMIO films deposited epitaxially on top of the BTO buffer layer are subject to a varying strain from compressive to tensile as the BTO thickness increases, driving the SMIO films from antiferromagnetic to ferromagnetic, and then back to antiferromagnetic, accompanied by a change from perpendicular to in-plane magnetic anisotropy. X-ray linear dichroism spectra reveal that the magnetic order and anisotropy in SMIO are associated with the preferential occupation of the Mn $d_{3z^2-r^2}$ or $d_{x^2-y^2}$ orbitals, which is controlled, in turn, by the epitaxial strain.

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• Magnetic anisotropy
• Magnetic order
• Complex oxides
• Magnetic thin films
• Magnetization measurements
• X-ray absorption spectroscopy
• X-ray diffraction
• X-ray photoelectron spectroscopy