Small angle critical scattering of neutrons by nickel

The critical magnetic scattering of neutrons by nickel was studied as a function of temperature and of the scattering vector κ in the range 0.008?0.04 Å^?1 for various specimens ranging from a single crystal to heavily deformed polycrystals. The shift of the temperature where the maximum of the scattered intensity is found as a function of scattering vector κ depends on the degree of crystalline imperfection. For the single crystal the observed shift is ΔT/T? 5 · 10^?3. On the basis of the Ornstein-Zernike theory the observed scattering by the single crystal yields the critical index (gamma = 2v = 1.32 pm _{0.14}^{0.20} ) as predicted by most of the theories.