Magnetism, spin fluctuations, and non-Fermi-liquid behavior in (UxLa1-x)(2)Zn-17 - art. no. 064413

We present results of the low-temperature specific heat C of samples of the series (UxLa1-x)(2)Zn-17, combined with measurements of the low-temperatur e magnetic susceptibility (chi) and resistivity (rho). For x>0.8 we find an tiferromagnetic order in coexistence with heavy-fermion behavior. An extrap olation of TN as a function of the uranium concentration implies that T-N v anishes for x = 0.8; at x = 0.8, no magnetic order is detected experimental ly at temperatures above 0.06 K. The non-Fermi-liquid (NFL) behavior predic ted at such a point in the magnetic phase diagram may be observed, but not as clearly as in other systems; some of the behavior is more consistent wit h spin fluctuations. As the uranium concentration is lowered below x = 0.8, C continues to rise in the low-temperature limit, while chi proportional t o chi (o) - a T-0.5, but ( seems to tend towards the behavior of a Fermi li quid with spin fluctuations at the lowest temperatures (T< 0.25 K). First a t x = 0.3 the temperature dependence of CIT is found to be contrary to Ferm i-liquid behavior, while <chi>(proportional to) chi (o) - a log T. Thus non -Fermi-liquid behavior is not found so unambiguously at the concentration w here TN vanishes as expected by a quantum critical point theory, but rather at lower uranium concentrations. This presents the possibility that NFL be havior in (UxLa1-x)(2)Zn-17 is not due to nearness to a quantum critical po int, but rather to disorder or the presence of spin fluctuations.