Spin dependent interface scattering, low temperature resistivity and magnetoresistance in NiFeCo/Cu superlattices

The temperature dependence of the resistivity and magnetoresistance rho(AF) - rho(F) of the NiFeCo (15 Angstrom)/Cu (t(Cu)) superlattices with t(Cu) = 9 and 21-22 Angstrom, characterized by different correlated interface roughness, is found to depend strongly on the nature of the dominant electron scattering centres in the interface zone, and is determined by that of the spin dependent interface resistivity. This explains why the magnetoresistance changes in a quite different manner with temperature from specimen to specimen. We propose, within the frame of a simplified two-current model, that the presence of spin fluctuations and/or spin glass states in the interface zone is responsible for the temperature dependent behaviour of the spin dependent interface resistivity. The main features of the derived interface resistivity data, such as a maximum at T-max similar or equal to 12 K for the specimen with t(Cu) = 9 Angstrom and a T-2, T-3/2 or T dependence for those with t(Cu) = 21-22 Angstrom, are explained satisfactorily in a unified picture of scattering of the electrons by spin fluctuations and/or spin glass states. The latter are in turn mediated appreciably by magnetic impurity concentration in the interface zone. The magnetoresistance at finite temperatures manifests itself to increase whenever the spin asymmetry is large, but to decrease with increasing magnetic impurity concentration in the interface zone.