The results of x-ray diffraction, magnetic susceptibility, and 155Gd Mössbauer spectroscopy studies of the recently discovered icosahedral quasicrystal Ag50In36Gd14 are reported. The studied quasicrystal has a simple six-dimensional Bravais lattice with the six-dimensional hypercubic lattice constant of 7.805(2) Å. The observed broadening of the diffraction Bragg peaks reflects the presence of the topological/chemical disorder. The temperature dependence of the magnetic susceptibility follows the Curie–Weiss law with an effective magnetic moment of 8.15(1) μB per Gd atom and the paramagnetic Curie temperature of −37.1(2) K. The studied quasicrystal is a spin glass with a freezing temperature of 4.25(5) K. The presence of a distribution of the electric quadrupole splitting in the Mössbauer spectra indicates the existence of a multiplicity of Gd sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, −4.91(10) × 1021 V cm−2 and η = 1.00(20). The Debye temperature of Ag50In36Gd14 is 199(2) K. The hyperfine magnetic field sets in at a temperature higher than the freezing temperature.

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.

We report on measurements of the dc and ac magnetic susceptibility, (155)Gd Mössbauer spectra, and specific heat of the 1/1 approximant Ag(50)In(36)Gd(14), and of the ac magnetic susceptibility of the icosahedral quasicrystal Ag(50)In(36)Gd(14). These alloys are shown to be spin glasses. For the icosahedral quasicrystal Ag(50)In(36)Gd(14), spin freezing occurs at T(f) = 4.3 K, and the frequency dependence of T(f) is well accounted for by the Vogel-Fulcher and power laws. Spin freezing in the 1/1 approximant Ag(50)In(36)Gd(14) occurs in two stages: at T(f(1)) = 3.7 K, Gd spins develop short-range correlations but continue to fluctuate, and then long-range freezing is achieved at T(f(2)) = 2.4 K. The frequency dependences of T(f(1)) and T(f(2)) can be accounted for by means of the Vogel-Fulcher law and the critical slowing down dynamics. It is shown that the spin freezing in both alloys is a nonequilibrium phenomenon rather than a true equilibrium phase transition. The (155)Gd Mössbauer spectra of the 1/1 approximant Ag(50)In(36)Gd(14) confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The magnetic specific heat exhibits a maximum at a temperature that is 30% larger than T(f(1)), but the temperature derivative of the magnetic entropy peaks at T(f(1)). The Debye temperature of the 1/1 approximant Ag(50)In(36)Gd(14) is 199(1) K as determined from the Mössbauer data, and 205(2) K as determined from the specific heat data.

No abstract