Papers by Author: S. Valencia

Abstract: In this work we present results of contact resistance between La2/3Ca1/3MnO3 (LCMO) and Pt system. LCMO epitaxial thin films have been grown by rf sputtering on top of LaAlO3 (LAO) substrate. The contact between the manganite film and the metal have been prepared by exsitu deposition of a 30 nm thick Pt layer on top of the manganite film by e-beam evaporation at room temperature. Different nanostructured contact geometries have been defined by using a focus ion beam system and then transport properties have been tested by means of AFM system working on the current sensing mode with a doped diamond tip. We show that the top-most LCMO layers do play a very relevant role on the transport properties acting as an insulating barrier. AFM measurements in the current sensing mode exhibit typical features of tunneling conduction. Ex-situ annealing in air at high temperature clearly improve the magnetotransport properties of the films reducing the surface insulating barrier. X-ray absorption spectroscopy measurement at the Mn Ledge has been performed to gain a deeper insight into the properties of the top-most LCMO layers.

Abstract: Magnetotransport properties of very high quality fully strained epitaxial thin films of La2/3Ca1/3MnO3 (LCMO), grown on top of SrTiO3 (STO) (001) substrates, are analyzed. As-grown fully strained epitaxial films are ferromagnetic and metallic but exhibit depressed transport and magnetic properties (low TC and MS). Detailed analysis of the structural and magnetotransport properties after high temperature annealing processes, have revealed a progressive structural relaxation, as detected by the variation of the c/a tetragonal distortion, as the annealing temperature rises up. Nevertheless, no changes in the in-plane cell parameters are observed. Simultaneously, the magnetic transition temperature, TC, and saturation magnetisation, MS, substantially increase approaching values similar to that of bulk materials.