Anisotropic magnetic, electrical, and thermal transport properties of the Y-Al-Ni-Co decagonal approximant
Physical Review B 78(10): 104204
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 Al76Co22Ni2. 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.