Resistivity and Thermopower of a Series of Ni–Fe Invar Alloys

The resistivity and absolute thermopower of a series of commercial f.c.c. Ni–Fe alloys containing 36–51 at. % Ni plus a comparison alloy of 75 at. % Ni have been measured over the range 1.5–125 K. Both the residual and the temperature dependent resistivities show a dramatic increase as the Ni concentration is reduced. By combining the present thermopower results with those at high temperatures by Kolomoets and Vedernikov, it is found that a pronounced maximum in the absolute magnitude of the thermopower occurs at a temperature of the order of 200–400 K. The results have been interpreted in terms of the 'weak ferromagnet' band model. Spin-mixing is briefly discussed and shown not to be of primary importance in these alloys.