Correlations between oxygen octahedral distortions and magnetic and transport properties in strained La0.5Sr0.5CoO3 thin films

Abstract

We quantitatively evaluated oxygen octahedral distortions in epitaxial thin films of the itinerant ferromagnet, ${\mathrm{La}}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3}$ (LSCO), and investigated their impact on strucure-property relationships. The compressively strained film on a $\mathrm{LaAl}{\mathrm{O}}_{3}$ substrate has a lower electrical resistivity and higher ferromagnetic transition temperature than the tensilely strained film on a ${\mathrm{La}}_{0.30}{\mathrm{Sr}}_{0.70}{\mathrm{Al}}_{0.65}{\mathrm{Ta}}_{0.35}{\mathrm{O}}_{3}$ 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.