Surface vs. bulk order/disorder transition in a binary alloy. A Hediffraction study of the $\rm Cu_3Au(001)$ surface

• Published in: Europhysics letters 1999-03, Vol.45 (6), p.686-692
• Main Authors: Mannori, C., Boato, G., Canepa, M., Cantini, P., Mattera, L., Terreni, S.
• Format: Article
• Language: English
• Subjects: 34.50.-s; 68.35.Rh
• ISSN: 0295-5075; 1286-4854
• DOI: 10.1209/epl/i1999-00222-0

We present a helium diffraction study of the order/disorder phase transition at the (001) surface of $\rm Cu_3Au$. We have measured the specular and the superlattice (-1, 0) Bragg intensities in the 140 K $\leq T\leq 800$ K temperature range. We have performed an accurate determination of the Debye-Waller factor, including anharmonic contributions. Thanks to the extreme surface sensitivity of helium diffraction, the superlattice peak intensity provides an experimental determination of the long-range order parameter M at the topmost surface layer. The surface critical temperature is found to be $T_{\rm c}^{\rm s}$ = $664\pm 2\;{\rm K}$. The value of the critical exponent $\beta $ = 0.45 ± 0.05 is in good agreement with theoretical predictions within the surface-induced disorder model.