Mn local structure in the decagonal phase of Al-Mn alloys.

Abstract

Our extended x-ray absorption fine-structure (EXAFS) results on the decagonal phase of Al-Mn alloys indicate that each Mn atom has on average about eight Al neighbors in the first-neighbor peak, compared to ten in the icosahedral phase. The decrease in the number of neighbors occurs in the low-distance part of the radial distribution function. These differences between the icosahedral- and decagonal-phase nearest-neighbor pair distribution functions, p(r), correlate with the changes in the fraction of magnetic and nonmagnetic sites observed in NMR, suggesting that the sharper part of p(r) is nonmagnetic and the broader part magnetic. These results suggest a model based on Al pentagons or distorted MacKay icosahedra, elongated along a fivefold axis.