  STM based magnetotransport measurements of epitaxial
La$_{0.7}$Sr$_{0.3}$MnO$_3$ 32 nm thick films with and without an internal
LaMnO$_3$ layer (0-8 nm thick) grown on Nb doped SrTiO$_3$ are presented. The
measurements reveal two types of low field magnetoresistance (LFMR) with a
magnitude of $\sim 0.1-1.5\%$. 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 LaMnO$_3$ layers. The other contribution originates from the
reverse biased Nb doped SrTiO$_3$ interface and the interface layer of
La$_{0.7}$Sr$_{0.3}$MnO$_3$. Both LFMR contributions display a field dependence
indicative of a higher coercivity ($\sim$200 Oe) than the bulk film. LaMnO$_3$
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.
