Evolution of magnetism and its interplay with superconductivity in heavy-fermion UPt3 doped with Pd

The pseudobinary series U(Pt1-xPdx)(3) demonstrates a wealth of magnetic and superconducting properties that are exemplary for heavy-fermion physics. In this paper, I present a survey of recent neutron-diffraction and muSR experiments, conducted to study the evolution of magnetism, and its interplay with superconductivity, in UPt3 doped with Pd. The small-moment antiferromagnetic order (SMAF) with T-N similar to 6 K reported for pure UPt3, is robust upon alloying till at least x = 0.005. The small ordered moment m(x) grows from 0.018mu(B)/U-atom for x = 0.00 to 0.048mu(B)/ U-atom for x = 0.005. TN of the SMAF phase does not vary with Pd content. The increase of m(x) correlates with the splitting AT, of the superconducting transition and provides evidence for a Ginzburg-Landau scenario for unconventional superconductivity with magnetism as symmetry-breaking field. The absence of a signal of the SMAF phase in zero-field muSR spectra provides strong evidence for a moment fluctuating at a rate > 10 MHz. A second large-moment antiferromagnetic phase (LMAF) is found at higher Pd concentrations. For this phase, at optimum doping (x = 0.05) T-N,T-max = 5.8 K and m = 0.62mu(B)/U-atom. The critical Pd concentration for the emergence of the LMAF phase is x(c,af) similar to 0.006. At the same Pd content, superconductivity is completely suppressed. The existence of a magnetic quantum critical point in the phase diagram, which coincides with the critical point for superconductivity (x(c,af) = x(c,sc) approximate to 0.006), yields evidence for odd-parity superconductivity mediated by ferromagnetic spin-fluctuations. (C) 2002 Elsevier Science B.V. All rights reserved.