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Anisotropic magnetic and transport properties of the orthorhombic Al13Co4 decagonal approximant

We have investigated anisotropic physical properties (magnetic susceptibility, electrical resistivity, thermoelectric power, Hall coefficient and thermal conductivity) of the o-Al13Co4 orthorhombic approximant to the decagonal phase. The crystalline-direction-dependent measurements were performed along the a, b and c directions of the orthorhombic unit cell, where (b, c) atomic planes are stacked along the perpendicular a direction. Magnetic susceptibility is predominantly determined by the Pauli spin paramagnetism of conduction electrons. The in-plane magnetism is stronger than that along the stacking a direction. Anisotropic electrical and thermal conductivities are the highest along the stacking a direction. The anisotropic thermoelectric power changes sign with the crystalline direction and so does the anisotropic Hall coefficient, which changes from negative electron-like to positive hole-like for different combinations of the electric current and magnetic field directions. The investigated anisotropic electrical and thermal transport coefficients were reproduced theoretically by ab-initio calculation using Boltzmann transport theory and the calculated anisotropic Fermi surface. The calculations were performed for two existing structural models of the o-Al13Co4 phase, where the more recent model gave better agreement, though still qualitative only, to the experiments. The physical properties of the o-Al13Co4 phase were compared to the literature data on two related decagonal approximant phases, the Y-Al-Ni-Co and the Al4(Cr, Fe), allowing for a study of the evolution of physical properties with increasing structural complexity and unit cell size. A comparison of the decagonal approximant phases to the decagonal Al-Ni-Co-type quasicrystals was made, too.

61.44.Br; 71.23.Ft

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