  We present a rectifying manganite-titanate heterojunction exhibiting a
magnetic field tunable depletion layer. This creates a large positive
magnetocapacitance, a direct measure of the field-induced reduction of the
effective depletion width across the junction. Furthermore, the reduction of
the junction barrier shifts the forward bias characteristics, giving
exponentially-enhanced differential magnetoresistance, occurring despite the
absence of a spin filter. These results provide a unique probe of a Mott
insulator/band insulator interface, and further suggest new electronic devices
incorporating the magnetic field sensitivity of these strongly correlated
electron materials.
