Strong dependence of oxygen octahedral distortions in SrRuO₃ films on types of substrate-induced epitaxial strain

This work investigates the effects of types of epitaxial strain on the structural and magneto-transport properties of SrRuO₃ (SRO) thin films grown on (110)_ortho NdGaO₃ (NGO) and (110)_ortho SmScO₃ (SSO) substrates that result in a -1.66% compressive strain and a +1.63% tensile strain, respectively. Although the epitaxial strains induced by the NGO and SSO substrates are almost equal in magnitude, the film properties were found to be strongly dependent on the type of strain. High-resolution scanning transmission electron microscopy revealed that the compressively strained SRO films possess a tetragonal structure with no octahedral tilts, while the tensilely strained SRO films undergo a thickness-dependent transition from a monoclinic structure with octahedral tilts to a tetragonal structure with small tilts. These findings indicate that octahedral tilt propagation from the substrate into the film is preferentially induced under tensile rather than compressive strain. We further found that the magneto-transport properties of SRO films exhibit a significant dependence on the type of the epitaxial strain, demonstrating the close correlation between strain-induced octahedral distortions and magnetic anisotropy. These results highlight the important role of the type of the epitaxial strain on the structural and physical properties of epitaxial thin films.