Thickness dependence of perpendicular magnetic anisotropy in La_0.7 Sr_0.3 MnO₃ films on LaAlO₃

We have studied the thickness dependence of magnetic domain patterns of magnetoresistive La_0.7 Sr_0.3 MnO₃ films on LaAlO₃ substrates using magnetic force microscopy. Maze-like domain patterns caused by perpendicular magnetic anisotropy were suddenly developed above the film thickness of ∼ 65 nm. This evolvement of magnetic domain pattern was consistent with the magnetic hysteresis data and it can be explained by a simple simulation based on the classical Kittel's model. The critical thickness for the appearance of perpendicular magnetic anisotropy is likely to be determined by a competition between the out-of-plane strain magnetic anisotropy and the in-plane shape anisotropy.