Magnetic excitations in the Zn-Mg-Tb icosahedral quasicrystal: An inelastic neutron scattering study

Taku J. Sato, Hiroyuki Takakura, An Pang Tsai, Kaoru Shibata

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    20 Citations (Scopus)

    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 (Tf 5.8 K). A single broad inelastic peak, centered at ω 2.5 meV, was observed in the inelastic scattering spectrum at temperatures ranging from the base temperature up to ∼20 K. The inelastic peak energy is Q independent, whereas the peak intensity shows weak Q 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 (ω<0.8 meV), we observed a strong quasielastic signal, appearing only above Tf; its peak width decreases as the temperature is lowered and vanishes at Tf. 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 Tf <T<20 K. The macroscopic freezing at Tf is, thus, attributed to a random freezing of spin-cluster fluctuations.

    Original languageEnglish
    Article number054417
    JournalPhysical Review B - Condensed Matter and Materials Physics
    Volume73
    Issue number5
    DOIs
    Publication statusPublished - 2006 Feb 28

    ASJC Scopus subject areas

    • Electronic, Optical and Magnetic Materials
    • Condensed Matter Physics

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