63Cu quadrupole-split nuclear magnetic resonance has been observed in the unconventional Kondo alloy UCu3.sPd15. The magnetic and quadrupolar line widths were measured as functions of temperature. Below ~ 30 K the magnetic line width is enhanced ~ 25% over the values expected by scaling the high-temperature magnetic susceptibility. This behavior might indicate the possibility of U-spin freezing, as observed in some dilute Kondo alloys. The absence of any anomaly at ~ 30 K in either the specific heat or the susceptibility suggests, however, that spin freezing does not account for the observations, and that the enhancement is related to intrinsic behavior of the paramagnetic alloy.
The intermetallic Kondo alloy UCu3.5Pdl.5 is one of a number of recently discovered Kondo materials which exhibit deviations from Fermi-liquid behavior down to the lowest attainable temperatures [1][2][3][4]. Competing models to explain the thermodynamic properties of these systems invoke either a modification of charge degrees of freedom below the Kondo temperature (e.g. the quadrupolar Kondo effect) [5], or critical phenomena associated with a magnetic phase transition at zero temperature [3,6]. 89y nuclear magnetic resonance (NMR) studies in one of these materials, Y0.sU0 2Pd3, yielded a substantial anomaly in the temperature dependence of the line shape [8]. The similar thermodynamic behavior of Yo.sUo.2Pd3 and UCu3.sPdL5 motivated NMR studies of the latter material. Cu nuclei in UCu3.sPdLs, unlike 89y nuclei.in YosUo.2Pd3, possess an electric quadrupole moment, and both charge and magnetic degrees of freedom can in principle affect the quadrupole-split NMR spectrum.
The structure of UCu3.sPdl. 5 introduces two complications to the NMR experiment: the fact that the * Corresponding author.