Small‐angle neutron scattering from cobalt in the critical region

The temperature dependence of the small‐angle critical scattering of neutrons from cobalt has been measured both above and below its Curie temperature, Tc. Below Tc the scattering is dominated by well‐defined spin wave modes which exhibit nearly quadratic dispersion. As Tc is approached, the spin waves renormalized and broaden but no evidence of the longitudinal component of the susceptibility is observed. Above Tc, the exponents γ=1.23±0.05 and ν=0.65±0.04, describing the power law dependences of the static susceptibility and the inverse correlation range, respectively, have been obtained from the small‐angle scans after taking full account of th einelasticity of the scattering. The energy widths of the scattering above Tc have been measured and are well described by a dynamical scaling function over a range of temperature and wave vector extending throughout the critical region and well into the hydrodynamic regime.