Suppression of spin-state transition in epitaxially strained LaCoO3
Abstract
Epitaxial thin films of LaCoO3 (E-LCO) exhibit ferromagnetic order with a transition temperature Tc = 85 K, while polycrystalline thin LaCoO3 films (P-LCO) remain paramagnetic. The temperature-dependent spin-state structure for both E-LCO and P-LCO was studied by x-ray absorption spectroscopy at the Co L2,3 and O K edges. Considerable spectral redistributions over temperature are observed for P-LCO. The spectra for E-LCO, on the other hand, do not show any significant changes for temperatures between 30 K and 450 K at both edges, indicating that the spin state remains constant and that the epitaxial strain inhibits any population of the low-spin (S = 0) state with decreasing temperature. This observation identifies an important prerequisite for ferromagnetism in E-LCO thin films.