Abstract: Ferromagnetic insulators are required for many new magnetic devices, such as dissipationless quantum-spintronic devices, magnetic tunneling junctions, etc. Ferromagnetic insulators with a high Curie temperature and a high-symmetry structure are critical integration with common single-crystalline oxide films or substrates. So far, the commonly used ferromagnetic insulators mostly possess low-symmetry structures associated with a poor growth quality and widespread properties. The few known high-symmetry materials either have extremely low Curie temperatures (≤16 K), or require chemical doping of an otherwise antiferromagnetic matrix. Here we present compelling evidence that the LaCoO₃ single-crystalline thin film under tensile strain is a rare undoped perovskite ferromagnetic insulator with a remarkably high TC of up to 90 K. Both experiments and first-principles calculations demonstrate tensile-strain–induced ferromagnetism which does not exist in bulk LaCoO₃. The ferromagnetism is strongest within a nearly stoichiometric structure, disappearing when the Co2+ defect concentration reaches about 10%. Significant impact of the research includes demonstration of a strain-induced high-temperature ferromagnetic insulator, successful elevation of the transition over the liquid-nitrogen temperature, and high potential for integration into large-area device fabrication processes.

Introduction: Dr. Xiaofang Zhai is currently an associate professor at Hefei National Laboratory for Physical Sciences at Microscale of University of Science and Technology of China. She earned her PhD degree from Physics department of University of Illinois at Urbana-Champaign and worked at University of California at Berkeley as a postdoc. She studies oxide thin films fabricated by pulsed laser deposition and oxide molecular beam epitaxy. Her current interests is focused on the emergent magnetism in low dimensional complex oxides, such as ultrathin films and superlattices. Her work involves a lot of collaborations with beamline scientists at synchrotron sites.