Local atomic and electronic structures of epitaxial strained LaCoO3thin films

Abstract

We have examined the atomic and electronic structures of perovskite lanthanum cobaltite (LaCoO${}_{3}$) thin films using Co $K$-edge x-ray absorption fine structure (XAFS) spectroscopy. Extended XAFS (EXAFS) demonstrates that a large difference between in-plane and out-of-plane Co-O bond lengths results from tetragonal distortion in highly strained films. The structural distortions are strongly coupled to the hybridization between atomic orbitals of the Co and O atoms, as shown by x-ray absorption near edge spectroscopy (XANES). Our results indicate that increased hybridization is not the cause of ferromagnetism in strained LaCoO${}_{3}$ films. Instead, we suggest that the strain-induced distortions of the oxygen octahedra increase the population of ${e}_{g}$ electrons and concurrently depopulate ${t}_{2g}$ electrons beyond a stabilization threshold for ferromagnetic order.