Magnetic Properties of Thin Films of Ferromagnetic Metals Produced by the Evaporation Method

Abstract

Magnetic properties of thin films of iron, nickel and cobalt.—The films were deposited by the evaporation method on tin or aluminum foil, and the magnetic properties studied by an induction method for fields up to 139 gauss. The thickness of the films varied from 20 to 300 millimicrons (mμ). The results are as follows. (1) The maximum value of the intensity of magnetization is of the same order of magnitude as for bulk metal. In the case of cobalt, however, it is evident from the curve that with higher fields values higher than any heretofore attained might be secured. The magnetization is independent of the crystal size and the thickness of the film. (2) The remanence is high for iron and cobalt. For nickel a low value was obtained, perhaps due to oxidation. The remanence depends on the crystal size but not on the thickness. (3) The coercive force is high for all three metals and changes abruptly to lower values as the thickness is increased beyond a critical value, which for iron, cobalt and nickel is about 55, 70 and 200 mμ respectively. The high values of the coercive force may be due to the minute size of the crystals in the films. (4) The results combined with Steinberg's curves for the Hall effect in films, tend to contradict Kundt's conclusion that the Hall e.m.f. is proportional to the intensity of magnetization.