A Calculation of the Electronic Structure of an Impurity Atom of Non-Transition Element in Transition Metals –The Nuclear Spin-Lattice Relaxation Time of an Impurity Atom (Al and Cu) in Pd–

Kohzuki and Asayama have shown that the nuclear spin-lattice relaxation time T 1 of Al in Pd 1- x Al x in the range of small x (<0.03) becomes about 10 times as long as that of pure Al and in the case of Pd 1- x Cu x , T 1 of Cu does not change appreciably in the whole range of x . These data are analysed in this paper by carrying out ab initio calculations of the electronic structure of a single impurity atom in Pd. It is shown that T 1 of Al nucleus is determined mainly by the contact interaction with conduction electrons. The increase of T 1 is a direct result of the reduction of the density of electrons with the Fermi energy at the impurity nucleus, ρ s (0, E F ), which arises from the fact that the Fermi level is situated at the valley between the bonding and antibonding states of the s states at the impurity site with the host d band. On the other hand, in the case of an impurity atom of Cu in Pd, the orbital relaxation, which can be neglected in pure Cu, compensates the decrease of the relaxation rate due to the contact interaction. The calculated T 1 's agree semiquantitatively with those obtained experimentally in both cases of Al and Cu. Some other data of T 1 of impurity nuclei in various transition metals are also discussed.