Low-temperature transport, thermal, and optical properties of single-grain quasicrystals of icosahedral phases in the Y-Mg-Zn and Tb-Mg-Zn alloy systems

We present a comprehensive series of results of electrical transport (electrical conductivity, magnetoconductivity, Hall effect), thermal (specific heat), and optical (reflectivity) measurements in varying temperature ranges between 1.5 and 300 K on high-quality single-grain quasicrystals of icosahedral Y-Mg-Zn. This data set is augmented by the specific-heat and optical-reflectivity data obtained from a single-grain quasicrystal of icosahedral Tb-Mg-Zn. For Y-Mg-Zn, both the electrical conductivity σ(T) and magnetoconductivity δσ(H) may be described by calculations considering quantum interference effects. A detailed comparison of the weak-localization contributions to σ(T) and δσ(H) with our experimental data provides estimates of the inelastic and spin-orbit relaxation rates. The inelastic relaxation rate is found to be proportional to T³. The dominant contributions to the optical conductivity σ₁(ω) spectrum, obtained from the reflectivity R(ω) data in the frequency range between 16 and 9.7×10⁴ cm^-1, are a strong Drude feature at low frequencies and a prominent absorption signal centered at approximately 6×10³ cm^-1. A comparison of the spectral weight of the Drude contribution to σ₁(ω) with the magnitude of the linear-in-T term γT of the low-temperature specific heat Cₚ(T) yields the itinerant charge-carrier density nᵢ=7.62×10²¹ cm^-3 or 0.13 charge carriers per atom. The low nᵢ value is corroborated by the results of the Hall effect measurements. For Tb-Mg-Zn, the optical conductivity σ₁(ω) spectrum reveals features similar to those of Y-Mg-Zn. The low-temperature specific heat Cₚ(T) of Tb-Mg-Zn is strongly influenced by a spin-glass-type freezing of Tb moments and by crystal-electric-field effects.