Influence of the oxygen content in the transport and magnetic properties of manganite thin films

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

Roma, Italia

Conferencia; International Conference on Magnetism; 2003

In the last years much effort has been made in order to study perovskite rare earth manganese oxides. The origin of this attention is the Colossal Magnetoresistance (CMR) observed in these compounds and the many possible applications of these systems, such as magnetic sensors or memory devices. The oxygen (O) content of the samples, affects the magnetic and transport properties of the samples, fixing the Mn3+/Mn4+ ratio. We present in this work a study of the physical properties of low-doped manganite films submitted to different oxidation processes. The O content of the samples has been changed by post-deposition annealings, performed at different O pressures and annealing times. La0.96Sr0.04MnO3 films were grown on SrTiO3 and MgO single-crystalline substrates by dc sputtering. The temperatures and magnetic field dependence of the magnetization (M) and the resistivity (r) have been measured to investigate the magnetic and transport properties of the samples. We have observed that the Curie temperature and the remanent magnetization of the films increase with increasing O content. Moreover, a drop of the r is measured when samples are submitted to the different annealing treatments. Also, the samples become more homogeneous after annealings and both the coercive fields and squareness of the M loops increase. These results suggest that as-grown samples have an important number of O vacancies that are reduced by post-deposition annealings. The r of as-grown LSMO/STO films is semiconductor-like but they present a metal-insulator transition in highly oxygenated samples. This effect could be related to a reduce of the samples disorder degree by annealing treatments inducing, as consequence, a decrease of the mobility edge in the films, below the Fermi energy, delocalizing the electronic states of the samples with high number of O vacancies. The reported effects are much more pronounced in films grown on SrTiO3 than in MgO ones. In summary, we have found that the variation of oxygen contents strongly affect the magnetic and transport properties of manganite thin films and that the oxidation dynamics depends critically on the strain fields of the samples.