LOCAL MOMENT FORMATION AND RESISTIVITY MINIMA IN COAL ALLOYS

Measurements of electrical resistivity, thermoelectric power, and magnetoresistance have been made from 1.4° to 300°K in alloys of 48%-57% cobalt in aluminum. At the equiatomic composition, CoAl has the CsCl structure. Resistance minima were observed in the vicinity of 30°K for cobalt concentrations between 50.4% and 51.5%. Below the resistance minima there is a temperature region where the dependence is approximately logarithmic before it saturates at about 1.4°K. The depth of the minima [ρ(1. 4°K)-ρ(Tmin)] and the thermopower at 4.2°K both show rather sharp peaks as a function of concentration in the vicinity of 50.5% cobalt. The magnetoresistance of the samples showing minima is negative or T<Tmin and its magnitude increases with field up to 150 kG. These results and earlier susceptibility measurements for this system are discussed in terms of several current theories of the electronic effects of magnetic impurities in metals. © 1969 The American Institute of Physics.