Al-27 and Cu-65 NMR study in UCn(5)Al

We have studied the microscopic properties of the tetragonal UCu5Al Kondo c ompound by Al-27 and Cu-63,Cu-65 NMR in the paramagnetic state. NMR and sus ceptibility measurements performed on the powdered sample, but oriented alo ng the applied field, showed chi(parallel to) > chi(perpendicular to). Plot s of K-parallel to(T) against chi(parallel to)(T) at temperatures T greater than or equal to 100 K yield the transferred hyperfine fields of +5.9 kOe/ mu(B), for Al-27 nuclei, and +5,3 and -7.0 kOe/mu(B), for Cu-65 nuclei in c rystallographically inequivalent Cu(2) and Cu(1) sites, respectively. The K night shift vs. susceptibility plots for T < 100 K exhibit a deviation from the linear behaviour (absolute values of shifts become smaller than expect ed). We attribute this finding to the crystalline electric field effect in similar way as it was reported for several Ce-based compounds. The random d istribution of the AL and Cu(2) atoms in the crystal lattice we consider as a reason of an unusual broadening of the NMR spectra, particularly at low temperatures. (C) 1999 Elsevier Science B.V. All rights reserved.