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 $B2\mathrm{}-{\mathrm{DO}}_3$ order-disorder transition. A speckle pattern was observed at the $\left(\frac{1}{2}\frac{1}{2}\frac{1}{2}\right)$ 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.