UC Santa Cruz

Abstract: The different magnetic behaviors of LaCoO$$_3$$ 3 films grown on LaAlO$$_3$$ 3 and SrTiO$$_3$$ 3 substrates are related to the Co–O–Co bond angles and the constraints imposed on the Co–O bond lengths by the substrate geometries. The observed magnetic behavior is not consistent with ferromagnetism. Rather, long-range antiferromagnetic order occurs below $$T \approx 90$$ T ≈ 90  K when the Co–O–Co bond angle is greater than 163$$^\circ$$ ∘ , consistent with the behavior of bulk and nanoparticles forms of LaCoO$$_3$$ 3 . A LaAlO$$_3$$ 3 substrate prevents magnetic long-range order at low temperatures near the film–substrate interface and collinear antiferromagnetic sublattices away from the interface. At low temperatures, the antiferromagnetically ordered sublattices are non-collinear in films grown on SrTiO$$_3$$ 3 substrates, leading to a significant net moment. The net moment is controlled by the geometry imposed by the substrate upon which the LaCO$$_3$$ 3 film is grown. Graphical abstract