Anisotropic magnetic and transport properties of orthorhombicAl13Co4

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We have investigated anisotropic physical properties (magnetic susceptibility, electrical resistivity, thermoelectric power, Hall coefficient, and thermal conductivity) of the $o{\text{-Al}}_{13}{\text{Co}}_{4}$, an orthorhombic approximant to the decagonal phase. The crystallographic-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 crystallographic direction and so does the anisotropic Hall coefficient which changes from negative electronlike to positive holelike 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 structural models of the $o{\text{-Al}}_{13}{\text{Co}}_{4}$ phase, where the more recent model gave better agreement, though still qualitative only, to the experiments.