Europhys. Lett., 63 (4) , pp. 597-602 (2003)
Magnetic-field dependence of the magnetic excitations in orderedN. Cavadini1, M. Schneider1, P. Allenspach1, P. C. Canfield2 and Ph. Bourges3
1 Laboratory for Neutron Scattering, ETH Zürich & Paul Scherrer Institut 5232 Villigen PSI, Switzerland
2 Ames Laboratory, Department of Physics and Astronomy, Iowa State University Ames, IA 50011, USA
3 Laboratoire Léon Brillouin, CEA/CNRS-Saclay 91191 Gif-sur-Yvette, France
(Received 10 December 2002; accepted in final form 16 June 2003)
The effect of an external magnetic field H on the magnetic excitations in ordered is investigated by inelastic neutron scattering on single crystals for the first time. A Zeeman-like renormalization of the magnetic excitations is observed at fixed T=2 and up to H=5 . Above the renormalization occurs linearly, following the expectation for the crystal electric-field levels at finite fields. However, in the range 0<H<1.1 clear discontinuities mark the successive metamagnetic transitions reported for the ground state of the title compound. The comparison of the magnetic excitations between the antiferromagnetic ( H<0.4 ), helicoidal ( ) and ferromagnetic ( ) ground state allows, by first principles, the determination of the leading exchange interactions between the rare-earth ions. The quantitative results are put into the context of recent theoretical models.
75.10.Dg - Crystal-field theory and spin Hamiltonians.
75.30.Et - Exchange and superexchange interactions.
78.70.Nx - Neutron inelastic scattering.
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