Anisotropic magnetic, electrical, and thermal transport properties of the Y-Al-Ni-Co decagonal approximant

We have investigated anisotropic physical properties (magnetic susceptibility, electrical resistivity, thermoelectric power, Hall coefficient, and thermal conductivity) of Y-Al-Ni-Co decagonal approximant with composition Al(76)Co(22)Ni(2). The crystalline-direction-dependent measurements were performed along three orthogonal directions a*,b, and c of the Y-Al-Ni-Co unit cell, where (a,c) monoclinic atomic planes are stacked along the perpendicular b direction. Anisotropic magnetic susceptibility of conduction electrons is paramagnetic for the field lying within the (a,c) atomic planes and diamagnetic for the field along the b direction. Anisotropic electrical resistivity is low in all crystalline directions, appearing in the order rho(a*)>rho(c)>>rho(b). Thermopower shows electron-phonon enhancement effect. Anisotropic bare thermopower (in the absence of electron-phonon interactions) was extracted, appearing in the same order as the resistivity, vertical bar S(a*)(bare)/T vertical bar>S(c)(bare)/T vertical bar>vertical bar S(b)(bare)/T vertical bar. Anisotropic thermal conductivity appears in the order kappa(b)>kappa(c)>kappa(a*), so that b is the most conducting direction for both electricity and heat. Hall coefficient R(H) exhibits pronounced anisotropy, where the magnetic field in a given crystalline direction yields the same R(H) for the current along the other two crystalline directions in the perpendicular plane. These anisotropies are analyzed in terms of the anisotropic structure of the Y-Al-Ni-Co phase and the ab initio calculated anisotropic Fermi surface. The results are compared with the literature-reported anisotropy of the physical properties of the d-Al-Ni-Co decagonal quasicrystal.