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

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Abstract
Kondo has shown that the resistance minimum in dilute alloys which exhibit localized magnetic moments arises from a resonant antiferromagnetic (JTk = T0 exp − [1/N(0) | J |], the conventional spin‐disorder scattering is dominated by this resonant scattering. Here T0 is of order the Fermi temperature, and N(0) is thedensity of states at the Fermi surface. Perturbation calculations of the susceptibility in powers of N(0) | J | valid for T>Tk 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.