A strain-addressed high temperature perovskite ferromagnetic insulator

Ferromagnetic insulators with a high Curie temperature and a high symmetry structure are critical for potentially being well integrated with common single crystalline oxide films or substrates. The commonly used ferromagnetic insulators are mostly with low symmetry structures associated with poor growth integrity. The only few investigated high symmetry materials either have very low Curie temperatures (≦16 K), or require chemical doping into an antiferromagnetic matrix. Here we demonstrated a tensile-strain addressed LaCoO₃ thin film to be the non-doped perovskite ferromagnetic insulator, yet with a remarkable transition temperature as high as 90 K. Both experiments and the first-principles calculation demonstrated that the tensile strain induced the intrinsically not existed ferromagnetism. The ferromagnetism reaches the strongest within a nearly stoichiometric structure, and disappears when the introduced Co²⁺ defect concentration reaches to a critical amount. Significance of the research includes the availability of a successful elevation of the transition over the liquid-nitrogen temperature and a high integration potential in the large area device fabrication.