Density functional studies of LaMnO3 under uniaxial strain

We study the electronic and magnetic properties of tetragonal LaMnO3 (LMO) under uniaxial strain, appropriate for epitaxially grown LMO heterostructures, from density functional calculations. The optimized tetragonal structure without strain has volume, magnetic order, and Jahn-Teller distortions similar to the bulk LMO, which forms in the orthorhombic structure. Strain affects the relative magnitudes of these distortions and changes the magnetic and conduction properties. While unstrained LMO is a type A antiferromagnet and insulating, we find that it changes to a ferromagnetic metal under tensile strain condition (c-axis stretched). The latter is the result of a diminishing magnitude of the Jahn-Teller distortion with strain, which in turn reduces the splitting of the Mn-eg orbitals, eventually leading to a metallic state, and finally to a ferromagnet due to the double exchange interaction. The calculated Poisson's ratio from geometry optimization agrees with the experimental values for the bulk.