Low-Temperature Resistivity and the Sign of the Exchange Integral

Kondo has predicted that a minimum should occur in the resistivity of alloys which exhibit a localized moment if they have a negative s-d exchange integral, and a logarithmic decrease in resistivity with decreasing temperature should take place for alloys with positive exchange. The exchange J is known from EPR measurements to be negative for gadolinium in palladium and positive for manganese in palladium. Measurements of resistivity as a function of temperature for several dilute alloys of Pd-Gd show no such minima, and no change in resistivity at the Curie point. The Pd-Mn alloys show a sudden linear decrease in resistivity below a temperature which varies with manganese concentration and which corresponds approximately to the magnetic transition temperature of the alloy.