Magnetic scaling of non-Fermi-liquid UCu_5-xPd_x (x = 0.8, 0.9, 1, 1.2)

The UCu_5-xPd_x heavy-fermion alloy system is known to exhibit non-Fermi-liquid (NFL) behaviour for compositions with x ≈ 1. The magnetic properties associated with NFL behaviour of this system are the focus of this study. Results are presented on the temperature (1.7 ≤ T ≤ 300 K) and magnetic field (0 ≤ B ≤ 5 T) dependences of the magnetization M and susceptibility χ for polycrystalline UCu_5-xPd_x samples with x = 0.8, 0.9, 1.0 and 1.2. We emphasize the observed field dependence of χ at low temperatures and illustrate the instability of NFL properties against magnetic field. Our χ (T) data present a systematic power-law divergence for NFL UCu_5-xPd_x at low temperatures in the limit of small measuring fields. This is interpreted in terms of Griffiths-phase singularities near a quantum critical point which are treated in a model given by Castro Neto and co-workers that includes the effects of structural disorder and a generic RKKY-Kondo interplay (where RKKY ≡ Ruderman-Kittel-Kasuya-Yosida). For the extended range 1.7 ≤ T ≤ 300 K, we find that χ(T) scales reasonably well with a theoretical expectation of Souletie and co-workers of NFL behaviour of Kondo systems. Finally, our M(T, B) data for magnetic fields up to 5 T and 1.7 ≤ T ≤ 21 K are shown to conform to a NFL scaling relation that applies to T = 0 quantum critical systems. The above analyses support the role that magnetic interactions are thought to play in NFL UCu_5-xPd_x.