Europhys. Lett., 64 (5) , pp. 689-695 (2003)
Magnetic Raman scattering of the ordered tetrahedral spin- clusters in ( 1-x x) 2 compoundsJ. Jensen1, P. Lemmens2 and C. Gros3
1 Ørsted Laboratory, Niels Bohr Institute - Universitetsparken 5 DK-2100 Copenhagen, Denmark
2 Max Planck Institute for Solid State Research - D-70569 Stuttgart, Germany
3 Fakultät 7, Theoretische Physik, Universität des Saarlands D-66041 Saarbrücken, Germany
(Received 1 April 2003; accepted in final form 17 September 2003)
Raman light-scattering experiments in the antiferromagnetic phase of the ( 1-x x) 2 compounds are analyzed in terms of a dimerized spin model for the tetrahedral -clusters. It is shown that the longitudinal magnetic excitation in the pure system hybridizes with a localized singlet excitation due to the presence of a Dzyaloshinskii-Moriya anisotropy term. The drastic change of the magnetic scattering intensities observed when a proportion of is replaced by ions, is proposed to be caused by a change of the magnetic order parameter. Instead of being parallel/antiparallel with each other, the spins in the two pairs of spin- order perpendicular to each other, when the composition x is larger than about 0.25.
75.10.-b - General theory and models of magnetic ordering.
75.30.-m - Intrinsic properties of magnetically ordered materials.
78.30.-j - Infrared and Raman spectra.
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