Neutron spin-echo study of URu2Si2

We have studied the magnetic correlations in the heavy-fermion superconduct or URu2Si2 using high-resolution neutron spin-echo techniques. The measurem ents confirm previous results that the weak ordered moment flips the neutro n spin, and hence is of dipolar origin. The spin-echo signal, with an energ y resolution two orders of magnitude better than earlier neutron experiment s, confirms the static nature of the moment, in agreement with muon measure ments. In addition, we found evidence for the presence of rapidly fluctuati ng magnetic moments in the ordered phase, which an most likely at the origi n of the enhancement of the linear term in the specific heat at low tempera tures. (C) 1999 Elsevier Science B.V. All rights reserved.