Critical Behavior of Iron Above its Curie Temperature

High-resolution measurements of the energy distribution of neutrons critically scattered in Fe establish that the hydrodynamic region in which conventional theory is valid extends only to values of the scattering $q\approx K_1$, where $K_1$ is the inverse of the spin correlation range. Analysis of data restricted to this region indicates that the susceptibility varies as ${(1-\frac{T_c}{T})}^{1.30\pm 0.06}$. Contrary to expectations, the spin-diffusion constant $\Lambda$ shows considerably less dependence on temperature, varying as ${(1-\frac{T_c}{T})}^{0.14\pm 0.04}$.