Cu-NMR and magnetization in disordered nFL system UCu$_4$Ni

We present a study of the NMR spectra in a random powder of UCu$_4$Ni as a function of frequency (40-70 MHz) and temperature (5-300 K). Two types of spectral lines for each of the two isotopes of naturally abundant Cu in the material are clearly evident in the spectra. Their behavior is followed for temperature and field variations and compared/contrasted with the more studied case of UCu$_4$Pd, where only one type of Cu-NMR line has been observed clearly. Unlike in UCu$_4$Pd, the appearance of two types of signal from Cu nuclei in the Ni compound is unambiguous evidence of site disorder in UCu$_4$Ni. This alone is indication that the amount of site disorder in the Ni sample is larger than in the Pd system; however, the NMR line intensities reveal that the Ni ions do not seem to go completely randomly in the two available crystallographic sites of the underlying crystal structure as would be expected from ionic-size considerations alone. The NMR parameters for both types of spectral lines, together with complementary measurements of magnetic susceptibility performed on the same powder samples, will be discussed from the point of view of magnetic disorder and non-Fermi liquid behavior.