Sustained coherent epitaxy and role of oxygen vacancies in La0.7Sr0.3MnO3−δ thin films grown on SrTiO3 by sputtering

Abstract

Ferromagnetic La0.7Sr0.3MnO3−δ (LSMO) epitaxial thin films of single-crystal quality with very smooth surfaces are grown on SrTiO3 (100) substrates by on-axis rf magnetron sputtering. We find that the resistivity and the spontaneous magnetization for these 180 nm thick films are nearly equal to those of single crystals after thermal annealing. On the other hand, the Curie temperature TC is no higher than 270 K, a value far below the bulk one, which is quite unusual. As a clue to this riddle, we note a strong correlation between the lattice constant for these films and the amount of oxygen vacancies in the case of LSMO, an oxygen-nonstoichiometric oxide. From this, we conclude that the sustained coherent epitaxy takes place to match the lattice mismatch of 0.8% by incorporating a limited amount of oxygen vacancies, which relaxes the film in-plane stress while functions to significantly reduce TC.