Point contact investigations of film and interface magnetoresistance of La0.7Sr0.3MnO3 heterostructures on Nb:SrTiO3

STM based magnetotransport measurements of epitaxial La0.7Sr0.3MnO3 31 nm thick films with and without an internal LaMnO3 layer (0-3.1 nm thick) grown on Nb doped SrTiO3 are presented. The measurements reveal two types of low field magnetoresistance (LFMR) with a magnitude of ~0.1-1.5%. One LFMR contribution is identified as a conventional grain boundary/domain wall scattering through the symmetric I-V characteristics, high dependence on tip placements and insensitivity to introduction of LaMnO3 layers. The other contribution originates from the reverse biased Nb doped SrTiO3 interface and the interface layer of La0.7Sr0.3MnO3. Both LFMR contributions display a field dependence indicative of a higher coercivity (~200 Oe) than the bulk film. LaMnO3 layers are found to reduce the rectifying properties of the junctions, and sub-micron lateral patterning by electron beam lithography enhances the diodic properties, in accordance with a proposed transport model based on the locality of the injected current.