Modifications of weak localization contributions to magnetoresistance due to magnetic impurities in amorphous DyxY1-xNi alloys (invited)

High-field magnetoresistance experiments performed on thick amorphous alloys offer a simple way to study three-dimensional (3D) weak localization of conduction electrons. After the precursor work of Fert et al. on nonmagnetic amorphous alloys, we found it interesting to study how these effects would disappear under substitutions of magnetic impurities (1% to 10% of Dy) in a nonmagnetic amorphous alloy (YNi). The experiments, performed between 1.5 to 50 K and in magnetic fields up to 20 T, showed (i) in YNi, characteristic features of the magnetoresistance due to weak localization under strong spin-orbit scattering and (ii) in DyxY1-xNi, a coexistence of weak localization effects with the classical contribution of spin alignment by the applied magnetic field, saturating at negative values. This last contribution dominates the behavior of Dy-richer samples whereas weak localization is clearly observed for x≤3%. In all the samples a dramatic increase of the initial magnetoresistance slope Δρ/ρH2 (where ρ=resistivity and H=applied field) is observed when magnetic impurity concentrations increase. We explain this increase of weak localization effects, in the framework of the available weak localization theory, by an enhancement of the Zeeman spin splitting due to interactions between localized (4f ) and delocalized (d, s) electronic states