Specific Heat of Pure Zinc and Some Zn-Mn Alloys

The specific heat of pure zinc and of Zn-Mn alloys containing 0.1 and 0.05 at.% Mn has been measured in the range 0.4 to 30°K. The excess entropy of the alloys, as compared with pure zinc, is about 2.5 cal/°K g atom manganese, indicating a spin of $\frac{3}{2}$ for the Mn atoms. At the lowest temperatures, the specific heat of the more concentrated alloy is linearly proportional to temperature. Above 12°K, the specific heats of both alloys become less than that of pure zinc—possibly a lattice effect due to the light "impurity." An alloy containing 0.2 at.% Mn was measured in the range 0.4 to 3°K, and below about 0.7°K the specific heat was the same as that of the 0.1-at.% Mn alloy, demonstrating the concentration independence of the limiting low-temperature specific heat. Measurements were also made below 1.5°K on an alloy containing 0.0007 at.% Mn. The superconducting transition temperature was depressed to about 0.5°K, rather lower than expected, and the transition remained of the second order. The variation of electrical resistance with temperature for all the samples was also measured. The temperature of the minimum was proportional to the $\frac{1}{5}$ power of the manganese concentration, in agreement with Kondo's prediction. A low-temperature maximum in the resistance was observed only for the 0.2-at.% Mn alloy.