Correlations between oxygen octahedral distortions and magnetic and transport properties in strained La0.5 Sr0.5Co O3 thin films

We quantitatively evaluated oxygen octahedral distortions in epitaxial thin films of the itinerant ferromagnet, La0.5Sr0.5CoO3 (LSCO), and investigated their impact on strucure-property relationships. The compressively strained film on a LaAlO3 substrate has a lower electrical resistivity and higher ferromagnetic transition temperature than the tensilely strained film on a La0.30Sr0.70Al0.65Ta0.35O3 substrate. The magnetic anisotropy is also found to depend on the type of strain, with perpendicular magnetic anisotropy induced in the compressively strained film and in-plane magnetization seen in the tensilely strained film. Our synchrotron x-ray-diffraction measurements and quantitative analysis reveal distinct oxygen octahedral distortions accommodated in these films and show that the out-of-plane and in-plane Co-O bond lengths of the compressively strained film are comparable to the in-plane and out-of-plane bond lengths of the tensilely strained film. These results indicate that the bond-length changes in LSCO modify hybridization between Co 3d and O2p orbitals, leading to the strain-dependent properties. These results highlight the significant role of octahedral distortions for structure-property relationships in the strained LSCO films.