Critical Magnetic Scattering of Neutrons in Iron

The intense small‐angle scattering of low‐energy neutrons by magnetic materials near the Curie temperature has been shown by Van Hove to be directly related to the appearance of large scale fluctuations in the spin density. We have measured the angular and energy distributions of 4.27‐Å neutrons scattered at small angles in iron and determined the spin correlation range 1/κ₁ and a parameter Λ associated with the lifetime of the fluctuations. Our results confirm the recent observation of Jacrot, Konstantinovic, Parette, and Cribier that the scattering is not elastic even at the Curie temperature. We have found that κ₁² varies as ${\mathrm{(T-T}}_c{)}^{\frac{4}{3}}$ for 0°<T−T_c<∼30°C as predicted by Domb and Sykes and by Gammel and Marshall and also that our measured values of κ₁ are in fair agreement with those predicted theoretically by Kocinski.