Spin correlations in uranium nitride near the ordering temperature

The spin correlations in cubic uranium nitride near the Néel temperature have been measured using two-axis and three-axis crystal spectrometer neutron scattering techniques. The spin correlations are found to be longitudinal in character and are spatially anisotropic. A dynamic scaling model is proposed which incorporates the anisotropy and is found to give a good description of the data. The exponents characterizing the temperature dependence of the inverse correlation length and susceptibility are close to those for the two-dimensional Ising model for $T>\mathrm{}{T}_N+4\mathrm{}$ K. The results are interpreted in terms of strong correlations within {001} sheets with weak correlations between sheets.