Magnetism, spin fluctuations, and non-Fermi-liquid behavior in (UxLa1-x)2Zn17

We present results of the low-temperature specific heat C of samples of the series (UxLa1-x)2Zn17, combined with measurements of the low-temperature magnetic susceptibility (χ) and resistivity (ρ). For x>0.8 we find antiferromagnetic order in coexistence with heavy-fermion behavior. An extrapolation of TN as a function of the uranium concentration implies that TN vanishes for x=0.8; at x=0.8, no magnetic order is detected experimentally at temperatures above 0.06 K. The non-Fermi-liquid (NFL) behavior predicted 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 with spin fluctuations. As the uranium concentration is lowered below x=0.8, C continues to rise in the low-temperature limit, while χ∝χ0-aT0.5, but C seems to tend towards the behavior of a Fermi liquid with spin fluctuations at the lowest temperatures (T<0.25 K). First at x=0.3 the temperature dependence of C/T is found to be contrary to Fermi-liquid behavior, while χ∝χ0-a log T. Thus non-Fermi-liquid behavior is not found so unambiguously at the concentration where TN vanishes as expected by a quantum critical point theory, but rather at lower uranium concentrations. This presents the possibility that NFL behavior in (UxLa1-x)2Zn17 is not due to nearness to a quantum critical point, but rather to disorder or the presence of spin fluctuations