Regensburg 2002 – scientific programme
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MA: Magnetismus
MA 21: Elektronentheorie
MA 21.5: Talk
Friday, March 15, 2002, 11:45–12:00, H22
Spin wave dispersion and Curie temperature in YFe2 and UFe2 — •L. Sandratskii1, L. Bergqvist2, O. Eriksson2, and P. Bruno1 — 1MPI für Mikrostrukturphysik, D-06120 Halle, Germany — 2Uppsala University, Box 534, SE-751 21 Uppsala, Sweden
Inelastic neutron diffraction experiment revealed a number of unusual features in the properties of YFe2 and UFe2. First feature is the absence of any observable mode involving the Y and U states. Second, the Fe-Fe exchange interaction as judged by the dispersion of the Fe mode is very strong. The parameter of the exchange interaction deduced from the value of the exchange stiffness in YFe2 is very close to the value for bcc-Fe and UFe2 is 5 times higher that in bcc-Fe. However, the value of the Curie temperature in UFe2, 165 K, is low and is much smaller than the value of the Curie temperature in YFe2, 545 K, or in bcc-Fe, 1043 K. We report parameter-free calculation of the spin-wave dispersion in YFe2 and UFe2. We show that though no inelastic scattering is detected from the Y and U cites the behavior of the magnetic moments of these atoms influences strongly the form of dispersion curve. For YFe2 we get good agreement with the experiment in the whole energy region of magnon excitations reported. For UFe2 we get good agreement with experiment in the low energy region (large spin stiffness) but strong softening of magnons in higher energy region. Exchange interactions in the system are discussed and relation between magnon softening and low Curie temperature in UFe2 is studied.