Muon spin rotation in the magnetic and superconducting ground states of (U,Th)Be13and (U,Th)Pt3<

Abstract

Microscopic aspects of magnetism and superconductivity have been studied in the heavy-fermion superconducting alloy systems (U,Th)Be» and (U,Th)Pt3 using the technique of positive-muon (p ) spin rotation and relaxation (pSR). In U& Th Be», x =0.033, a striking increase of zero-field Kubo-Toyabe relaxation rate o. KT is observed below the temperature T,2-0.4 K at which a second phase transition occurs in the superconducting state. This jump is firm evidence for the onset of weak static magnetism below T,&. The observed increase of -1.5 Oe in the p+ local field corresponds to an effective moment of 10 -10 pz/U atom. The p+ Knight shift K" in the normal states of U& Th, Be», x =0 and 0.033, is proportional to the bulk susceptibility and yields a transferred f-spin-p, " hyperfine field of -1.99+0.12 kOe/ps. In the superconducting states of U&, Th Be», x =0, 0.01, and 0.033, a large reduction of the magnitude of K" is observed for x =0 but not for x =0.033, and an intermediate reduction is found for x =0.01. This behavior suggests (1) spin-singlet pairing in undoped UBe», and (2) conventional reduction of the spin susceptibility suppression in (U,Th)Be» by spin-orbit scattering from Th impurities. In undoped UPt3 small increases of a&T and the transverse-field Gaussian relaxation rate o. G below -6 K are again evidence for the onset of weak static magnetism similar to that found in (U,Th)Be». Recent spin-polarized neutron scattering studies of normal-state UPt3 have observed a commensurate antiferromagnetic (AF) structure with a sublattice magnetization of -10 pz/U atom, in rough agreement with the pSR results. For U& Th Pt3, x =0. 05, zero-field p+ precession frequencies below 6.5 K indicate an AF structure with a considerably larger moment (-0.6 pz/U atom). The average p+ Knight shift in the normal state of undoped UPt3 is much smaller than in UBe», which suggests multiple p+ stopping sites with hyperfine couplings of opposite signs.

Absence of zero field muon spin relaxation induced by superconductivity in the B phase of UPt3

“…We note that the ∆ KT value observed at high temperature is consistent with the one found previously [16,4,5].…”

“…The increase of ∆ KT detected by the authors of Ref. [16] could be a consequence of a modification of the muon stoping site due to a larger concentration of impurities or defects in the sample.…”

Neutron-diffraction study of the evolution of antiferromagnetic order inUPt3doped with Pd

“…40, but this result has not been reproduced). In the course of a detailed investigation [9] of the evolution of magnetism in U(Pt,Pd) 3 by the µSR technique, we found that LMAF gives rise to a spontaneous µ + precession frequency.…”

Meta-stable states in the low-field magnetostriction of UPt3

“…Superconductivity co-exists with antiferromagnetic order. The formation of an antiferromagnetically ordered state below T, = 6 K is revealed by neutron diffraction measurements [3] and supported by muon spin rotation measurements [4]. The uranium moments are oriented along the b-axis of the hexagonal lattice.…”