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

Abstract

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 s(T) and magnetoconductivity ds(H) may be described by calculations considering quantum interference effects. A detailed comparison of the weak-localization contributions to s(T) and ds(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 s 1(v) spectrum, obtained from the reflectivity R(v) data in the frequency range between 16 and 9.7310 4 cm 21 , are a strong Drude feature at low frequencies and a prominent absorption signal centered at approximately 6 310 3 cm 21 . A comparison of the spectral weight of the Drude contribution to s 1(v) with the magnitude of the linear-in-T term gT of the low-temperature specific heat Cp(T) yields the itinerant charge-carrier density ni57.62310 21 cm 23 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 s 1(v) 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 crystalelectric-field effects.