Strain-induced insulating ferromagnetism in LaMnO3 thin films from first-principles investigations

Previous experiments have found that LaMnO3 thin films grown on SrTiO3 substrate exhibit insulating ferromagnetism different from that of the bulk LaMnO3. Utilizing first-principles calculations based on density functional theory, magnetic transitions, energy gaps and spin exchange interactions of LaMnO3 thin films with different epitaxial strains are investigated, and the effect of the Jahn-Teller distortion, rotation and tilt of oxygen octahedrons on magnetic and electrical properties are analyzed in detail. A relative narrow insulating ferromagnetic area without structural phase transition is obtained during the transition from metallic ferromagnetic phase to insulating A-type antiferromagnetic phase. If the magnetic transition of LaMnO3 film is attributed to Jahn-Teller distortion, then the metal-insulator transition should be ascribed to the tilt of the oxygen octahedron and large change of the O1-Mn-O2 angle in ab plane, which is helpful to understand the insulating ferromagnetic characters during the preparations of the LaMnO3 superlattices or heterostructures, also indicates that the insulating ferromagnetic properties of LaMnO3 films can be tuned by epitaxial strain-controlled oxygen octahedrons distortions.