Effect of (1 1 1)-oriented strain on the structure and magnetic properties of La_0.7Sr_0.3MnO₃ thin films

Using strain, i.e. subtle changes in lattice constant in a thin film induced by the underlying substrate, opens up intriguing new ways to control material properties. We present a study of the effects of strain on structural and ferromagnetic properties of (1 1 1)_pc-oriented La_0.7Sr_0.3MnO₃ epitaxial thin films grown on NdGaO₃, SrTiO₃, and DyScO₃ substrates. (The subscript pc denotes the pseudo-cubic symmetry.) The results show that La_0.7Sr_0.3MnO₃ assumes a monoclinic unit cell on NdGaO₃ and DyScO₃ and a rhombohedral unit cell on SrTiO₃. For La_0.7Sr_0.3MnO₃ on NdGaO₃ and DyScO₃ a uniaxial magnetic anisotropy is found, while La_0.7Sr_0.3MnO₃ on SrTiO₃ is magnetically isotropic. The Néel model is used to explain the anisotropy of the thin films on NdGaO₃ and SrTiO₃, however, for La_0.7Sr_0.3MnO₃ on DyScO₃ the effect of octahedral rotations needs to be included through the single ion model. Through examination of the Curie temperature of the strained films we suggest that (1 1 1)-strain has a different effect on the Jahn-Teller splitting of e _g and t _2g electron levels than what is seen in (0 0 1)_pc-oriented La_0.7Sr_0.3MnO₃ thin films.