The Lorenz Parameter in Dilute Silver-Manganese Alloys at Liquid Helium Temperatures

Abstract

Thermal conductivity data at liquid helium temperatures, on poly-crystalline rods of three dilute silver alloys (containing respectively 0.55, 0.32 and 0.14 at.% of manganese in solid solution) in magnetic fields ranging from 0 to 25 kilogauss, have been analysed afresh. The electronic and lattice components of the thermal conductivity are separated by the method of Gruneisen and de Haas. It is inferred that the electronic Lorenz parameter Le (i) is independent of the magnetic field but varies with the temperature in the liquid helium region, (ii) exhibits a minimum at a temperature which increases with the increase in manganese content, and (iii) is much smaller than the normal ` Sommerfeld ' value, but seems to extrapolate to that value at about 1°K. This behaviour of Le is explained on the basis of inelastic scattering of the conduction electrons by the magnetic impurity centres having closely spaced energy states, for such an inelastic scattering would contribute considerably to the electronic thermal resistivity while making only a small contribution to the electrical resistivity. Further, since such a scattering cannot occur at 0°K, Le should approach the normal value at the lowest temperatures.