Observation of low-energy magnetic response in the heavy-fermion compound UBe13.

Abstract

Inelastic-neutron-scattering experiments have been used to examine the low-frequency (2 meV) response of polycrystalline samples of the heavy-fermion ${\mathrm{UBe}}_{13}$. A quasielastic response with a characteristic linewidth of 1.5 meV for T>1 K is found. Surprisingly we found no anomalous dependence of this response on q, the reduced reciprocal lattice vector. The strength of the response corresponds to \ensuremath{\sim}60% of the bulk susceptibility, and it scales with the latter for 1.5T30 K. Taking into account earlier experiments the total response function for ${\mathrm{UBe}}_{13}$ thus contains two components, one with a linewidth of 1.5 meV and the other [A. I. Goldman et al., Phys. Rev. B 33, 1627 (1986)] with a linewidth of \ensuremath{\sim}13 meV. The weight is approximately evenly divided between the two. ${\mathrm{UBe}}_{13}$ is therefore similar to ${\mathrm{UPt}}_{3}$ in that the magnetic response functions exist on two quite different energy scales. This appears different from Ce-based heavy fermions, and is not yet understood.