Low-frequency electrical resistance of iron, cobalt, and nickel in the vicinity of their Curie temperatures

Abstract

Alternating-current electrical resistance measurements between 17 Hz and 100 kHz were made on high purity Fe, Co, and Ni wires in the vicinity of their Curie temperatures (Tc). The electrical resistance was independent of frequency for temperatures (T) aboveTc. As the temperature was lowered, however, there was an abrupt jump in the electrical resistance atTc followed by a gradual decrease toward its dc value. The magnitude of the electrical resistance jump atTc increased as the square root of the frequency. The enhancement of the electrical resistance forT≦Tc is produced by an abrupt decrease of the skin depth atTc which, in turn, is due to the sudden increase in the initial magnetic permeability atTc. Measurements of the ac electrical resistance in the vicinity of the Curie temperature of certain ferromagnetic metals can be utilized to 1) accurately determine the Curie temperature using frequencies as low as 17 Hz, and 2) quantitatively determine the initial magnetic permeability as a function of temperature and heat treatment.