Magnetic and transport properties of the giant-unit-cell Al3.26Mg2 complex metallic alloy

The β-Al3Mg2 complex metallic alloy comprises about 1168 atoms in the giant-unit cell, making this material excellent candidate to investigate how the exceptional structural complexity and the coexistence of two different length scales – one defined by the unit-cell parameters and the other by the cluster substructure – affect physical properties of a metallic material. We have investigated magnetic, electrical, thermal transport and thermoelectric properties of a monocrystalline and a polycrystalline Al3.26Mg2 sample in a mixed β–β′ phase, grown by the Czochralski technique. Electrical resistivity is in the range ρ ≈ 30–40 μΩ cm and exhibits T2 dependence at low temperatures and T at higher temperatures, resembling nonmagnetic amorphous alloys. Magnetic susceptibility χ measurements revealed that the samples are Pauli paramagnets with significant Landau diamagnetic orbital contribution. The susceptibility exhibits a weak increase towards higher temperature. Combined analysis of the ρ(T) and χ(T), 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 about 90% of the DOS of the fcc Al metal. Thermal conductivity contains electronic, Debye and hopping of localized vibration terms, whereas the thermopower is small and negative. High structural complexity of the β-Al3Mg2 complex metallic alloy does not result in high complexity of its electronic structure. We found no evidence for the existence of a pseudogap in the DOS at EF.