Enhanced transport properties in La_xMnO_(3.5) thin films grown on SrTiO_3 substrates

摘要

We report on structural, magnetic, and transport properties of La_xMnO_(3.5) thin films, epitaxially grown on SrTiO_3 substrates by molecular beam epitaxy deposition technique. We varied the La/Mn ratio by changing the evaporation rate of the single-element diffusive cells. However, the oxygen content of La_xMnO_(3.5) thin films was varied by post-annealing them in air and/or vacuum, by changing the annealing temperature and the time of post-annealing process. Optimal oxygenated La_(0.88)MnO_(3-δ) (LMO) films show extremely high metal insulator transitions temperature T_(MI) ～ 380K and magneto-transport similar to those found in strontium-doped La_(1-x)Sr_xMnO_3 manganites compounds. Magnetic measurements confirm the formation of a ferromagnetic phase at Curie temperature T_c of about 360K. All these findings clearly demonstrate that the lanthanum deficiency, with respect to bivalent cation-substitution, is a very efficient way to hole-dope manganites.