The Kondo Effect—The Link Between Magnetic and Nonmagnetic Impurities in Metals?

Kondo has shown that the resistance minimum in dilute alloys which exhibit localized magnetic moments arises from a resonant antiferromagnetic (JTk show that this exchange scattering acts to reduce the magnitude of the localized moment by inducing a localized polarization of the conduction electrons which partially compensates the impurity moment. More complete analysis indicates that the susceptibility, which for T≫Tk has a Curie-law term, saturates at a finite value for T≪Tk. This suggests that at least some of the alloy systems which are traditionally viewed as nonmagnetic in the context of the Friedel-Anderson type of Hartree-Fock analysis, are best described in terms of Kondo compensated magnetic impurities. To check this view, the properties of an exchange model with a realistic exchange integral are being worked out. One finds that the resistivity of the (nonmagnetic) Al based 3-d metal alloys is largest at the center of the 3-d series, dropping on either side, in agreement with experiment. Since these experiments are conventionally quoted as evidence for the validity of the Hartree-Fock treatment, further comparisons with experiment are necessary to resolve the question. Other results of the analysis and experimental evidence for the temperature dependent spin compensation are discussed.