Influence of the oxygen content and disorder in the transport properties of manganite films

M. SIRENA; N. HABERKORN; M. GRANADA; L. B. STEREN; J. GUIMPEL

S. C. de Bariloche, Argnetina

Conferencia; PASI on Physics at the Nanonometer Scale; 2003

Half-metallic manganite films are excellent candidates for technological applications such as magnetic reading devices, tunnel junctions for MRAM, etc. Manganites also present a high degree of correlation between the transport, magnetic and structural properties that is the origin of many exciting phenomena. All these have renewed the interest in these compounds in the last years. Some groups have seen that changing the oxygen content in manganite films and bulk compounds modifies the transport and magnetic properties of the samples. Although, a recent study on (La1-xNdx)0.7Sr0.3MnO3 thin films report only a weak dependence of the transport properties of the samples with the oxygen pressure during samples deposition. In order to study the oxidation dynamics in this system and its effect in the transport properties of manganite thin films, we have grown manganite films of La0.96Sr0.04MnO3 over different substrates (MgO and SrTiO3). The transport and magnetic properties of these films have been studied for different oxidation processes. We have changed the oxygen content in the samples by post-deposition annealing at different oxidation pressures and annealing times. Substrate induced strains stabilize a ferromagnetic ground  state for La0.96Sr0.04MnO3 thin films, in contrast with the bulk compound which is canted antiferromagnetic. The Curie temperature (TC)and the conductivity of the samples increase when the annealing time or the oxygen pressure is increased.We have studied the transport properties of the samples in the high temperature (HT) regime (T>TC) and the low temperature (LT) regime (T<TC). In the HT regime the resistivity is thermally activated and the activation energy doesn´t change significatively with the oxygen content. In the LT regime, films grown over STO present a metal-insulator transition as the structural disorder, i.e. oxygen vacancies, is reduced. In general, the most strained films (grown over STO) present a much more important change in the magnetic and transport properties with the different annealing processes, than those grown over MGO, indicating that oxidation dynamics in these systems is greatly affected by the strain field in the samples.