Enhanced transport properties in LaxMnO3-δ thin films epitaxially grown on SrTiO3 substrates: The profound impact of the oxygen content

We report on structural, magnetic, and transport properties of LaxMnO3-delta (LMO) thin films, epitaxially grown on SrTiO3 substrates by molecular beam epitaxy. Transport properties were investigated as a function of the La/Mn stoichiometry and the oxygen content. Optimal oxygenated LMO films (with stoichiometry ratio La/Mn=0.88) show a metal-insulator transitions temperature T-MI similar to 387 K and magnetotransport similar to those found in strontium-doped La1-xSrxMnO3 manganites compounds. Also in presence of a La/Mn slight unbalance (namely, x=0.98), LMO films show a very high T-MI similar to 370 K. However, LMO samples with La/Mn ratio larger than one, show severely depressed conducting properties, being insulating for x > 1.10. All these findings clearly demonstrate that the lanthanum deficiency is a very efficient way to dope manganites, as in the case of bivalent cation-substitution. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3168649]