Microscopic mechanisms of giant magnetoresistance

We present magnetoresistance measurements aimed at answering several open q uestions in the understanding of giant magnetoresistance (GMR). Our measure ments are performed on (F1/N/F2/N) multilayers in which N is a nonmagnetic metal (Cu or Cr), and F1 and F2 are various ferromagnetic metals or alloys. In current perpendicular to the plane (CPP) measurements on (F1/Cu/Co/Cu) multilayers, where Fl is Fe, Co, or Ni doped with impurities, we observe an inversion of the GMR for V or Cr impurities; this demonstrates, first the importance of the extrinsic effects in GMR and secondly the possibility of obtaining negative as well as positive values of the bulk spin asymmetry co efficient beta. A compensation thickness with zero GMR is found when the bu lk and interface spin asymmetry have opposite signs in the same layer. We i nterpret the sign of beta in models of electronic structure. Measurements o n other series of multilayers allow us to show that the interface spin asym metry coefficient gamma can also be positive (interfaces with Cu) or negati ve (interfaces with Cr). Finally, the comparison between CPP and CIP data o btained on the same samples sheds light on the different role of the interf ace intrinsic potential in the two geometries. [S0163-1829(99)09133-X].