Critical Scattering of Neutrons from RbMnF3

Abstract

Measurements of the inelastic magnetic scattering of neutrons from RbMnF₃ in the vicinity of the critical point are presented and compared with the predictions of the dynamic‐scaling proposal of Halperin and Hohenberg. At the Néel point, the energy dependence of the scattering for various wavevectors q is well represented by a universal three‐peaked function in which the component widths and separations are all proportional to q^1.4±0.2, in excellent agreement with the concept of scaling as well as with the specific prediction of an exponent of 1.5. In the hydrodynamic region above T_N (q small compared to the inverse‐range parameter, κ) the scattering is Lorentzian in energy. The half‐width at q=0 is proportional to κ^1.4±0.2, once again in good agreement with the scaling prediction. Over a broad region of the q, κ plane (T≥T_N), where resolution corrections can be omitted, the ``half‐area'' energy widths can be represented by a simple homogeneous function of q and κ, confirming the basic assumption of dynamic scaling.