Transport and superconducting properties of the Mg32(Al,Zn)49-type quasicrystalline and crystalline phases.

Abstract

We have investigated the transport and superconducting properties of the ${\mathrm{Mg}}_{32}$(Al,Zn${)}_{49}$-type icosahedral (I) and Frank-Kasper (FK) phases. All measurements were performed on single-phase samples. The I and FK phases of ${\mathrm{Al}}_{52.4}$${\mathrm{Cu}}_{12.6}$${\mathrm{Mg}}_{35}$ are superconducting below 0.81 and 0.73 K, respectively. Their electronic densities of states at the Fermi energy were obtained from upper-critical-field measurements. The I phase has (1) a higher low-temperature (4.2 K) resistivity of \ensuremath{\approxeq}58 \ensuremath{\mu}\ensuremath{\Omega} cm compared with \ensuremath{\approxeq}23 \ensuremath{\mu}\ensuremath{\Omega} cm for the FK phase and (2) a lower renormalized density of states of \ensuremath{\approxeq}0.52 states/eV?om versus \ensuremath{\approxeq}0.89 states/eV?om for the FK phase. The results are discussed with respect to theoretical models. Fitting magnetoresistance data of the I phase to localization theory gives a spin-orbit scattering time of \ensuremath{\approxeq}5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$ sec and an inelastic scattering time inversely proportional to ${T}^{2}$. The resistivities of the I and FK phases of ${\mathrm{Al}}_{20.2}$${\mathrm{Zn}}_{40.3}$${\mathrm{Mg}}_{39.5}$ are also measured, and superconductivity is not detected down to \ensuremath{\approxeq}0.3 K. The transport properties of these icosahedral quasicrystals are compared with other I-phase alloys containing d valence electrons.