Stress-induced surface magnetization of (La0.7Sr0.3)MnO3 thin films

The role of stress on magnetic properties of epitaxial (La0.7Sr0.3)MnO3 (LSMO) films has been studied. We have investigated 1100 angstroms thick LSMO films deposited on LaAlO3 (Sample L, under a compressive stress) and SrTiO3 (Sample S, under a tensile stress) using the magnetic force microscopy (MFM), DC hysteresis loop, ferromagnetic resonance (FMR) measurements. The magnetic force microscope image of Sample S shows a `maze-like' pattern indicating a sizable out-of-plane magnetization, while the magnetic image of Sample S shows a `feather-like' pattern indicative of an in-plane magnetization. The hysteresis loop and ferromagnetic resonance measurements give quantitative evidence for the role of the lattice mismatch between the film and the substrate in the magnetic anisotropy of the two films. Our systematic examination of various thickness LSMO films on LaAlO3 reveals that the maze pattern is exhibited only between 500 angstroms and 1700 angstroms thick films. Despite of larger anisotropy, no maze pattern is observed in films thinner than 360 angstroms.