Abstract
A theory is given of the temperature dependence of the hyperfine field H(T) assuming that spin wave excitations are dominant. It is shown that at constant volume the coefficient of T3/2 in H(T)/H(0) is identical to that in the reduced magnetization so that the hyperfine coupling constant takes the form A=1-cT5/2+O(T7/2), in agreement with Riedi's NMR work on iron (1973). A similar result holds for alloys and is consistent with measurements on FeAl alloys.