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 sigma(T) and magnetoconductivity delta sigma(H) may be described by calculations considering quantum interference effects. A detailed comparison of the weak-localization contributions to sigma(T) and delta sigma(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 T-3. The dominant contributions to the optical conductivity sigma(1)(omega) spectrum, obtained from the reflectivity R(omega) data in the frequency range between 16 and 9.7 X 10(4) cm(-1), are a strong Drude feature at low frequencies and a prominent absorption signal centered at approximately 6 X 10(3) cm(-1). A comparison of the spectral weight of the Drude contribution to sigma(1)(omega) with the magnitude of the linear-in-ir term gamma T of the low-temperature specific heat C-p(T) yields the itinerant charge-carrier density n(i) = 7.62 X 10(21) 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 sigma(1)(omega) spectrum reveals features similar to those of Y-Mg-Zn. The low-temperature specific heat C-P(T) of Tb-Mg-Zn is strongly influenced by a spin-glass-type freezing of Tb moments and by crystal-electric-field effects.