Pinhole and tunneling conduction channels superimposed in magnetic   tunnel junction: results and inferences
  The influence of ballistic channels superimposed on tunneling conduction channels in magnetic tunnel junctions has been studied in a manganese oxide based tunneling device. Inversion of 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 parallel conduction channels consisting of 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. The results seem to resolve a controversy regarding ballistic magnetoresistance in ferromagnetic nanocontacts and establishes that ballistic magnetoresistance do exist even if the previous results are attributed to magnetostriction and magnetostatic force related artifacts. 
Soumik Mukhopadhyay, I. Das