X-Ray Intensity Fluctuation Spectroscopy Observations of Critical Dynamics in Fe3Al

Abstract

We have carried out intensity fluctuation spectroscopy measurements using coherent x rays to study the dynamics of critical fluctuations in a binary alloy at equilibrium. An intense coherent hard x-ray beam, produced from an undulator source, was scattered from a single crystal of ${\mathrm{Fe}}_{3}\mathrm{Al}$ held at temperatures near the $B2\ensuremath{-}{\mathrm{DO}}_{3}$ order-disorder transition. A speckle pattern was observed at the $(\frac{1}{2}\frac{1}{2}\frac{1}{2})$ superlattice reflection. Below ${T}_{c}$ it was essentially static, while above ${T}_{c}$ it fluctuated in time. The behavior of the normalized time correlation function is consistent with predictions of theory.