UFe2 is a ferromagnet with Tc = 165 K. Previous neutron elastic measurements have established that the Fe moment is 0.6 mb and that the moment on the U atom is almost zero because of the cancellation of the spin and orbital moments, which are both about 0.23 mb, but are oppositely directed. We have now examined the spin dynamics from a large single crystal with both thermal and cold-source triple-axis spectrometers. Comaprisons with the extensive work performed on RFe2 (R = Tb, Ho, Er) suggests that two dispersive modes should be seen at low energy (i.e. less than ca. 20 meV). However, only one mode has been found in UFe2 and this involves the precession of the Fe spins. We propose that the acoustic mode involving the uranium spin is sufficiently broadened in (q, w) that we cannot readily detect the excitation. Nevertheless, the influence of the U-Fe exchange may be seen in (a) the presence of a gap in the Fe spin-wave spectrum at q+0, and (b) in an increase in the Fe spin-wave stiffness constant (D) as compared to that found in pure Fe.

PAOLASINI Luigi;  LANDER Gerard Heath;  SHAPIRO S.M.;  CACIUFFO R.;  LEBECH B.;  REGNAULT L.P.;  ROESSLI B.;  FOURNIER J.M.; 

1996-08-09

JRC13150

https://publications.jrc.ec.europa.eu/repository/handle/JRC13150,