Role of Spin-Nonconserving Forces in the Critical Dynamics of Fe at the Curie Point

Modern, high-resolution neutron-scattering techniques, in particular neutron spin echo, were applied to reinvestigate the critical dynamics of iron at temperatures above the Curie point. It was found that previously claimed evidence for a crossover was in error, and that the dynamical scaling hypothesis unexpectedly breaks down at small wave numbers. This breakdown is shown to be due to spin-nonconserving forces, which are tentatively identified with the thermodynamic random fields.