Magnetic response in UBe13

Uranium-based heavy-fermion superconductors have attracted interest because of the opportunity to study the interplay between magnetism and supercondu ctivity. All of these materials have been found to order antiferromagnetica lly with T-N > T-c with the exception of UBe13 in which no neutron evidence for static magnetism has been reported. In experiments on single crystals at Riso National Lab., we have observed antiferromagnetic short-range magne tic correlations situated at q = < 0.5,0.5,0 >. Their breadth in q-space sh ows that the correlations are short range; while the absence of a signal in certain directions suggests that the components we observe are longitudina lly polarised with respect to their propagation vector. In energy space, th e correlations extend to similar to 2 meV and no signal is observable for T > 30 K. The remaining question concerns the energy dependence of this resp onse around T-c. (C) 2000 Elsevier Science B.V. All rights reserved.