Ferromagnetism and Charge Order from a Frozen Electron Configuration in Strained Epitaxial LaCoO3

We report ordering of the cobalt electron configuration in ferromagnetic strained epitaxial LaCoO3. Specifically, the presence of charge order is demonstrated from distinct features of the resonant cobalt contribution to superstructure reflections. Density functional theory calculations show that the observed order is consistent with the spin-state periodicity predicted to give rise to ferromagnetism in LaCoO3. Through the modification of symmetry by strain, concurrent frozen charge and spin-state order are stabilized, giving rise to long-range magnetic order.