Atomic structure of the i- R -Cd quasicrystals and consequences for magnetism
Résumé
We report on the six-dimensional (6-D) structural refinement of three members of the i-R-Cd quasicrystals (R = Gd, Dy, Tm) via synchrotron X-ray diffraction from single grain samples, and show that this series is isostructural to the i-YbCd5.7 quasicrystal. However, our refinements suggest that the R occupancy on the Yb icosahedron sites within the Tsai-type atomic cluster is approximately 80%, with the balance taken up by Cd. Similarities between the i-R-Cd series and i-ScZn7.33, and their differences with i-YbCd5.7 and i-Ca15Cd85, indicate that there are at least two subclasses of Tsai-type icosahedral quasicrystals. We further show, from magnetization and X-ray resonant magnetic scattering (XRMS) measurements on a set of closely related Tb1−xYxCd6 1/1 approximants, that site disorder on the nominal R icosahedron within the Tsai-type cluster may contribute to the absence of long-range magnetic ordering in the binary i-R-Cd quasicrystals.