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Magnetic, transport and thermoelectric properties of Al-Cr-Fe quasicrystalline approximants

Two stable quasicrystalline approximants in the Al-Cr-Fe system-a gamma-brass phase ( -AlCrFe) and a mixture of two orthorhombic approximants of the decagonal phase (O1/O2-AlCrFe)-were investigated by magnetic susceptibility, electrical resistivity, thermal conductivity and thermoelectric power measurements, combined with structural investigations by X-ray diffraction, light microscopy (LM) and scanning electron microscopy (SEM). The investigated approximants exhibit physical properties that are in many respects intermediate to regular metals and quasicrystals (QCs). Their electrical resistivities show very weak temperature dependences and the resistivity values are in between regular metals and Al-based QCs. The magnetic susceptibility results show the existence of a small fraction (of about 1 % for the -AlCrFe and about ten times less for the O1/O2-AlCrFe) of localized magnetic moments with Curie-like temperature dependence. Thermal conductivity measurements show that the electronic and lattice contributions are of comparable size. While the electronic contribution can be described by the Wiedemann-Franz law, the lattice contribution can be reproduced by a sum of a Debye (long-wavelength phonons) and fracton hopping terms. At the lowest measured temperature (8 K), scattering of phonons on stacking-faults-like defects limits the heat transport, where this type of defects has also been observed in the LM and SEM structural investigations. The presented results indicate that the magnetic and transport physical properties of quasicrystalline approximants are not determined by the short-range atomic order only, but are affected by both, the short-range quasiperiodic and long-range periodic atomic orders.

magnetic susceptibility; electrical resistivity; thermal conductivity and thermoelectric power measurements; structural investigations; AlCrFe

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