  Low temperature (10K) high voltage bias dynamic conductivity (up to 2.7V) and
shot noise (up to 1V) were studied in epitaxial Fe(100)/Fe-C/MgO(100)/Fe(100)
magnetic tunnel junctions, as a function of the magnetic state. The junctions
show large tunnel magnetoresistance (185% at 300K and 330% at 4K). Multiple
sign inversion of the magnetoresistance is observed for bias polarity when the
electrons scan the electronic structure of the bottom Fe-C interface. The
shot-noise shows a Poissonian character. This demonstrates a pure spin
dependent direct tunneling mechanism and validates the high structural quality
of the MgO barrier.
