Direct measurement of ferromagnetic ordering in biaxially strained LaCoO_3 thin films

摘要

LaCoO_3 undergoes a transition from a nonmagnetic to a paramagnetic semiconductor at 80 K, associated with a spin-state transition of the Co~(3+) ions. It was proposed that the temperature of the spin-state transition depends strongly on the LaCoO_3 lattice parameter, suggesting that strain can stabilize different spin states at different temperatures. By combining atomic-resolution Z-contrast imaging, electron diffraction, and angular-resolved electron energy-loss spectroscopy (EELS) with in situ cooling experiments, we show that epitaxially strained LaCoO_3 (001) thin films grown on LaAlO_3 (001) do not undergo a low temperature spin-state transition. Our EELS study explores the origins of the ferromagnetic ordering in strained LaCoO_3 films.