  Inverse magnetoresistance has been observed in magnetic tunnel junctions with
pinhole nanocontacts over a broad temperature range. The tunnel
magnetoresistance undergoes a change of sign at higher bias and temperature.
This phenomenon is attributed to the competition between the spin conserved
ballistic transport through the pinhole contact where the transmission
probability is close to unity and spin polarized tunneling across the
insulating spacer with weak transmittivity.
