Strain driven magnetism in thin films of LaCoO3

The electronic structure of epitaxial films on LaCoO3(LCO) has been studied within first principle electronic structure calculations. A spin state transition is found to take place as a function of lattice strain which freezes in the intermediate spin state for non zero strain. In contrast to earlier speculations this is found to arise from substrate strain alone and angle variations are small. The intermediate spin state also stabilizes ferromagnetism in the ground state. The anomalous temperature dependence of the X-ray absorption spectra for films of LCO on LCO and its absence in films of LCO on (LaAlO_{3})_{0.3}(SrAlTaO_{6})_{0.7}$(LSAT) is also explained.