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The structural, magnetic, and Mössbauer spectral properties of the icosahedral quasicrystal Zn 77 Fe 7 Sc 16 are reported. The thermodynamically stable quasicrystal Zn 77 Fe 7 Sc 16 has a primitive six-dimensional Bravais lattice at room temperature with a six-dimensional hypercubic lattice constant of 7.087͑1͒ Å. Based on dc magnetization measurements, no evidence is found for a transition to a ground state with long-range magnetic order in the temperature range between 2 and 300 K. The dc zero-field-cooled and field-cooled susceptibility data indicate that the studied quasicrystal is a spin glass with freezing temperature T f = 7.75͑2͒ K. This is further confirmed by observing aging effects through the dc zero-field-cooled magnetization and the thermoremanent magnetization time decays and by the analysis of the frequency dependence of T f using the Vogel-Fulcher law and the dynamic scaling behavior near T f . However, the observed increase in the thermoremanent magnetization with the magnetic field in the low-field regime is incompatible with the ultrametrically organized phase space of a canonical spin glass. The nature of the spin-glass state of the icosahedral quasicrystal Zn 77 Fe 7 Sc 16 is therefore fundamentally different from that of a canonical spin glass. The bimodal distribution of the electric quadrupole splitting and of the hyperfine magnetic field derived from Mössbauer spectra indicates the existence of two classes of Fe sites.

The 151 Eu Mössbauer effect study in the temperature range 2.2-299.5 K on pulverized single crystals of EuCu 2 Si 2 synthesized from an indium flux is presented. In contrast to previous studies on polycrystalline samples in which valence fluctuations for Eu were reported, we find that the Eu atoms are divalent in the whole temperature range. Therefore, there are no charge fluctuations of Eu in EuCu 2 Si 2 .

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