Effect of strain-modulated lattice distortion on the magnetic properties of LaMnO3 films

LaMnO3 films with various thicknesses were deposited on LaAlO3 (001) single crystal substrate using a pulsed laser deposition technique (PLD) at oxygen pressure of 7.5 mTorr to probe how strain affects the magnetic properties. Results show that the magnetic transition temperature (Tc) is enhanced about 3.4% as the thickness increasing from 13.9 to 88.5 nm. Meanwhile, the saturation magnetization significantly increases almost 110.3%. The out-of-plane lattice parameter c was found to decrease from 3.97 Å to 3.94 Å with increasing the thickness of the film from 13.9 to 88.5 nm because of the compressive-strain relaxation. Temperature dependence of Raman scattering for all the films were measured to investigate the lattice distortion in the films at different strain. It was found that the softening of the lattice distortion model was suppressed at low temperature by the compressive strain. The decreased Tc and saturation magnetization are ascribed to the strain-modulated lattice distortion and thus the orbital-spin-phonon (OSP) coupling.