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−δ (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 TMI∼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 TMI∼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.