Study of Spin Dynamics in Iron with Slow Neutrons

Inelastic scattering of slow neutrons in iron has been studied over a wide temperature range, from temperatures well below Tc, where spin wave modes are well defined, through the critical region in the neighborhood of Tc to temperatures above Tc where diffusive modes are dominant. Below Tc, in the temperature range 0.005<(1−T/Tc)<0.2, the spin-wave energies vary as (1−T/Tc)0.37±0.03. Slightly below Tc the spin waves become over-critically damped. There is no indication of a peak corresponding to a diffusive mode. Above Tc a well defined hydrodynamic region exists in which the scattering is accurately described by diffusion theory. Both the static susceptibility and the spin-diffusion constant are found to vary as (1−Tc/T)ρ over the temperature range 0.008(1−Tc/T)<0.05, For the static susceptibility the value of ρ is 1.30±0.06, in reasonable agreement with theory; however, for the spin-diffusion constant it is 0.14±0.04 which is considerably smaller than expectations.