ANISOTROPIC HYBRIDIZATION IN SOME CERIUM AND URANIUM-COMPOUNDS WITH HEXAGONAL ZRNIAL-TYPE STRUCTURE

Recent experimental results on the magnetic and transport properties of monocrystalline RTIn (R = Ce and Nd; T = Ni and Pd) and UPdIn having the hexagonal ZrNiAl-type structure are presented and discussed in relation to the anisotropic hybridization effects. For CeTIn and UPdIn, the magnetic susceptibility-chi and electrical resistivity rho-along the a and c axes are significantly anisotropic and exhibit a remarkable contrast; chi-a > chi-c and rho-a almost-equal-to 3-rho-c for CeNiIn, chi-c > chi-a and rho-a almost-equal-to 1.5-rho-c for CePdIn, and chi-c > chi-a and rho-c > rho-a for UPdIn. On the monocrystalline NdTIn with stable 4f3 electrons, the bare crystal electric field (CEF) parameters in the ZrNiAl-type crystal are deduced from magnetic measurements. From the comparison of the anisotropy in chi-calculated from the bare CEF parameters with the observed anisotropy, we argue that the anisotropic hybridization effect of the f electrons with ligand s, p and d electron states plays an important role in the anisotropy in the magnetic and transport properties of the cerium and actinide compounds.