UNUSUAL FE-FE INTERACTIONS IN THE ITINERANT MAGNET UFE2

The dynamics of the cubic Laves phase ferromagnet UFe2 (T-C = 165 K) h ave recently been reported up to a maximum energy transfer of similar to 7 meV. The most surprising aspect is the strong Fe-Fe interactions as judged by the dispersion of the Fe only mode, and the absence of an y observable mode involving the U 5f electrons. Using the IN8 triple-a xis spectrometer at the ILL we have now extended these measurements to similar to 20 meV. The steep dispersion observed at low energy contin ues to similar to 10 meV. Between 12 and 17 meV the Fe mode is broad a nd difficult to observe. and it appears to interact with another mode, almost certainly nuclear (phonon) in origin. Above 17 meV we observe the mode again, although with a reduced dispersion. (C) 1998 Elsevier Science B.V. All rights reserved.