Spin fluctuations and anisotropic nuclear relaxation in single-crystal UPt3.

Abstract

The anisotropy and temperature dependence of the $^{195}\mathrm{Pt}$ spin-lattice relaxation rate ${\mathit{T}}_{1}^{\mathrm{\ensuremath{-}}1}$ have been measured in a single crystal of the heavy-fermion compound ${\mathrm{UPt}}_{3}$. Between 1.5 and 4.2 K ${\mathit{T}}_{1}^{\mathrm{\ensuremath{-}}1}$ is proportional to temperature. The observed anisotropy ${\mathit{T}}_{1\mathrm{?}}^{\mathrm{\ensuremath{-}}1}$/${\mathit{T}}_{1\mathrm{\ensuremath{\perp}}}^{\mathrm{\ensuremath{-}}1}$=1.7\ifmmode\pm\else\textpm\fi{}0.1, together with the nearly isotropic $^{195}\mathrm{Pt}$ hyperfine field, imply that the spin fluctuations are predominantly in the basal plane. The Korringa product is close to the value expected for a noninteracting Fermi gas, which indicates that the relaxation is not enhanced by antiferromagnetic (AFM) fluctuations. The effective fluctuation rates derived from these NMR data (9\ifmmode\pm\else\textpm\fi{}1 meV) and from inelastic neutron scattering by AFM fluctuations are similar, indicating that a rate of this order characterizes a range of fluctuation wave vectors.