engleski

Electrical, magnetic, thermal transport and thermoelectric properties of the "Bergman phase" Mg_32(Al, Zn)_49 complex metallic alloy

The Mg-Al-Zn system of intermetallics contains an exceptional crystalline phase Mg_32(Al, Zn)_49, named the Bergman phase, whose crystal structure is based on a periodic arrangement of icosahedral Bergman clusters within the giant unit cell, so that periodic and quasiperiodic atomic orders compete in determining the physical properties of the material. We have investigated electrical, magnetic, thermal and thermoelectric properties of a monocrystalline Bergman-phase sample of composition Mg_29.4(Al, Zn)_51.6, grown by the Bridgman technique. The electrical resistivity is in the range and exhibits a positive temperature coefficient with dependence at low temperatures and at higher temperatures, resembling nonmagnetic amorphous alloys. Magnetic susceptibility measurements revealed that the sample is a Pauli paramagnet with a significant Landau diamagnetic orbital contribution. The susceptibility exhibits a weak increase towards higher temperatures. Combined analysis of and , together with the independent determination of the Pauli susceptibility via the NMR Knight shift suggests that the observed temperature dependence originates from the mean-free-path effect on the orbital susceptibility. The electronic density of states (DOS) at the Fermi energy EF was estimated by NMR and was found to amount 72 % of the DOS of the fcc Al metal, with no evidence for the existence of a pseudogap. Thermal conductivity contains electronic, Debye and hopping of localized vibrations terms, whereas thermopower is small and negative. The high structural complexity of the Bergman phase does not result in high complexity of its electronic structure.

complex intermetallic alloys; physical properties

This work was supported in a part by the 6th Framework EU Network of Excellence 'Complex Metallic Alloys' (Contract No. NMP3-CT-2005-500140)