Thickness dependent uniaxial magnetic anisotropy due to step-edges in (1 1 1)-oriented La0.7Sr0.3MnO3 thin films

The magnetic anisotropy of films of La_0.7Sr_0.3MnO₃ grown on vicinal (1 1 1)-oriented SrTiO₃ substrates are investigated. For temperatures above the tetragonal – cubic structural phase transition temperature of the substrate, a step edge induced uniaxial magnetic anisotropy is found at remanence, with a thickness-driven change in easy axis direction, from perpendicular to the step edges to parallel to the step edges with increasing thickness. The anisotropy constant for the investigated (1 1 1)-oriented samples is of the same magnitude as for previously reported (0 0 1)-oriented samples. The data is discussed in the framework of in-plane rotations of the oxygen octahedra resulting in a uniaxial anisotropy. Furthermore, the magnetic anisotropy is sensitive to the structural phase transition at 105 K of the substrate, and the anisotropy constant increases drastically as the temperature is lowered below 105 K.