Abstract
Low-temperature spin dynamics in the face-centered-icosahedral Zn-Mg-Tb quasicrystal has been investigated by inelastic neutron scattering around its spin-glass-like freezing temperature . A single broad inelastic peak, centered at , was observed in the inelastic scattering spectrum at temperatures ranging from the base temperature up to . The inelastic peak energy is independent, whereas the peak intensity shows weak dependence, which is qualitatively similar to that observed for the elastic diffuse scattering. The inelasticity of spin excitations is hardly seen in canonical spin glasses and thus is a distinct feature of the Zn-Mg-Tb quasicrystal. We argue, with an aide of numerical simulation, that this broad inelastic peak can be interpreted as localized collective fluctuations of short-range-ordered spins in a dodecahedral spin cluster. In a much lower-energy region , we observed a strong quasielastic signal, appearing only above ; its peak width decreases as the temperature is lowered and vanishes at . It is thus evident that the quasielastic signal corresponds to a slow spin dynamics that freezes at the macroscopic freezing temperature. The coexistence of the inelastic peak and quasielastic signal suggests that the short-range order in the single cluster is robustly formed but is dynamic for . The macroscopic freezing at is, thus, attributed to a random freezing of spin-cluster fluctuations.
2 More- Received 4 October 2005
DOI:https://doi.org/10.1103/PhysRevB.73.054417
©2006 American Physical Society