paper

Strong coupling of Jahn-Teller distortion to oxygen-octahedron rotation and functional properties in epitaxially-strained orthorhombic LaMnO

arXiv:1307.3347 · doi:10.1103/PhysRevB.88.174426

Abstract

First-principles calculations reveal a large cooperative coupling of Jahn-Teller (JT) distortion to oxygen-octahedron rotations in perovskite LaMnO. The combination of the two distortions is responsible for stabilizing the strongly orthorhombic -AFM insulating () ground state relative to a metallic ferromagnetic (FM-) phase. However, epitaxial strain due to coherent matching to a crystalline substrate can change the relative stability of the two states. In particular, coherent matching to a square-lattice substrate favors the less orthorhombic FM- phase, with the -AFM phase stabilized at higher values of tensile epitaxial strain due to its larger volume per formula unit, resulting in a coupled magnetic and metal-insulator transition at a critical strain close to 1%. At the phase boundary, colossal magneto-resistance is expected. Tensile epitaxial strain enhances the JT distortion and opens the band gap in the -AFM- - phase, offering the opportunity for band-gap engineering. Compressive epitaxial strain induces an orientational transition within the FM- phase from - to - with a change in the direction of the magnetic easy axis relative to the substrate, yielding strain-controlled magnetization at the phase boundary. The strong couplings between the JT distortion, the oxygen-octahedron rotations and the magnetic and electronic properties, and associated functional behavior, motivate interest in other orthorhombic perovskites with large JT distortions, which should also exhibit a rich variety of coupled magnetic, structural and electronic phase transitions driven by epitaxial strain.

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