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The transmission of thermal neutrons through magnetized iron has been measured in its dependence upon the percentage deviation from saturation and upon the thickness d of the sample. In agreement with the theory of Halpern and Holstein it was found that the percentage increase of transmission caused by magnetization is given by (n^{2p^2d^2}2) f (), where n is the number of iron atoms per unit volume. Writing for the scattering cross section of neutrons with parallel or antiparallel orientation of their spin with respect to the field, respectively ₀, we find p=2. 00. 110^-24 cm^2. From the determined value of the length =3. 20. 310^-3 cm, the linear dimensions of the microcrystals can be determined to be =1. 410^-4 cm. For a thickness d=3. 8 cm a transmission effect of almost 8 percent was observed if the magnetization was brought to within 2. 5 per mille of its saturation value; more than twice this effect can be expected from the same thickness at complete saturation.
Bloch et al. (1943) studied this question.