The Intrinsic Fields in Ferromagnetic Substances

Abstract

FROM many points of view it seems evident that the so-called molecular field introduced by P. Weiss into the theory of ferromagnetism cannot be purely magnetic. The magnitude of such a field, if responsible for the ferromagnetic phenomena, would be of the order of 107 gauss (in the saturated state). On the other hand, a purely magnetic field of the same order of magnitude, as W. Voigt has pointed out, is required for accounting for the enormous Faradayor Kerr-effect in ferromagnetic substances. The study of this effect in the infra-red part of the spectrum (where the classical theory of free electrons in metals is fairly valid) seems to make it probable that the so-called free electrons moving between the atoms of iron or nickel are influenced by intrinsic magnetic fields of the order of 107 gauss. Thus two independent sources seem to make probable the existence of such enormous magnetic fields. Since both methods are, however, more or less indirect, it seemed worth while to work out a direct experimental method which could give some information as to the fields existing inside a ferromagnetic substance.