Buffer layer-induced positive magnetoresistance in manganite-based heterojunctions

Effects of the LaMnO3 (LMO) buffer layer on the magnetoresistive behaviors of La(0.67)A(0.33)MnO(3)/LaMnO3/SrTiO3:0.05 wt% Nb (LAMO/LMO/STON, A = Ca, Sr) have been experimentally studied. In addition to an enhanced response to a magnetic field, the current-voltage relations show a downward shift in magnetic field, indicating an increase of the junction resistance. It is completely different from that observed in the junctions without buffer layer. The positive magnetoresistance (MR) is strongly dependent on the thickness of the LMO layer, increasing first then decreasing with the increase of layer thickness. Furthermore, it is significantly stronger in LCMO/LMO/STON than in LSMO/LMO/STON. The maximal MR at 50 K is similar to 90% for LCMO/LMO/STON and similar to 52% for LSMO/LMO/STON, occurring at the LMO thickness of 4 nm under the field of 5 T. The MR persists up to 350 K, and it is similar to 30% and similar to 24% for the LCMO and LSMO junctions, respectively. An analysis of the current-voltage characteristics indicates an increase in interfacial barrier in magnetic field, which is the origin for the positive MR. (C) 2012 American Institute of Physics. [doi:10.1063/1.3673858]