Measurements of thermoelectricity below 1°K—IV

Abstract

Abstract IT is well known that metals such as copper may show anomalous resistive and thermoelectrio behaviour at low temperatures. It now seems clear (cf. Gold et al. 1960) that the large negative thermoelectric power which develops at temperatures of the order of 10°K to 20°K in certain specimens of the ‘pure’ metal or specially prepared dilute alloys must be attributed primarily to the presence of very small quantities of iron in solid solution. It also appears that other magnetic ions in solid solution will give rise to similar behaviour (cf. e.g. Jacobs and Schmitt 1959). It has been suggested (Schmitt 1956, cf. also Brailsford and Overhauser 1959) that, for example, the appearance of a maximum (and consequently also a minimum) in the electrical resistance at low temperatures can be explained in terms of scattering by magnetic impurity ions, if the spin degeneracy of the ground state is split and the electron scattering cross sections of the lower levels are higher than those of the upper levels. No detailed analysis appears to have been made of the thermoelectric behaviour to be expected on such a model, but it is suggested (cf. Schmitt loc. cit.) that this might be predicted if due account is taken of the inelastic electron scattering involved. One might remark that the experimental situation is to some extent complicated by the fact that electron scattering by excited lattice vibrations (phonons) becomes important above, say, 15°K in Cu in comparison with electron scattering by impurity sites.