Magnetoresistance through spin polarized p-states
  We present a theoretical study of the ballistic magnetoresistance in Ni contacts using first-principles, atomistic electronic-structure calculations. In particular we investigate the role of defects in the contact region in order to explain the recently observed spectacular magnetoresistance ratio. Our results predict that possible presence of spin polarized oxygen in the contact region, could explain conductance changes by an order of magnitude. Electronic transport essentially occurs through spin-polarized oxygen p states, and this mechanism gives a much higher magnetoresistance than that obtained assuming clean atomically sharp domain walls alone. 
Nikos Papanikolaou