Impurity-induced tuning of quantum well states in spin-dependent   resonant tunneling
  We report exact model calculations of the spin-dependent tunneling in double magnetic tunnel junctions in the presence of impurities in the well. We show that the impurity can tune selectively the spin channels giving rise to a wide variety of interesting and novel transport phenomena. The tunneling magnetoresistance, the spin polarization and the local current can be dramatically enhanced or suppressed by impurities. The underlying mechanism is the impurity-induced shift of the quantum well states (QWS) which depends on the impurity potential, impurity position and the symmetry of the QWS. 
A. Kalitsov, A. Coho, N. Kioussis, A. Vedyayev, M. Chshiev and A.   Granovsky