Substrate effect on the magnetic behavior of manganite films

The film thickness (t) dependence of the magnetic properties of La0.6Sr0.4M nO3 (LSMO) films grown on (001) MgO and (001) SrTiO3 substrates has been st udied. Hysteresis loops measured at low temperature show a smooth increase of the retentivity accompanied by a decrease of the coercitive field as the film thickness increases. The increase of coercitivity with decreasing t c an be interpreted in terms of a change in the domain structure of the films mainly due to an augmentation of domain pinning defects. The magnetic anis otropy has been measured using ferromagnetic resonance (FMR). A volume (VA) and a surface (SA) anisotropy contribution have been deduced from FMR angu lar dependence studies for both series of samples. In the LSMO films grown on MgO a VA component that corresponds to an easy-axis perpendicular to the plane of the films has been found while in contrast, the LSMO films grown on SrTiO3 present an easy-plane anisotropy. The SA is positive for both ser ies favoring a perpendicular magnetic anisotropy. The measured magnetic ani sotropy has been assigned to substrate-induced effects. (C) 2000 American I nstitute of Physics. [S0021-8979(00)55708-9].