Europhys. Lett.
Volume 64, Number 5, December 2003
Page(s) 689 - 695
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 November 2003
DOI: 10.1209/epl/i2003-00281-7
Europhys. Lett., 64 (5) , pp. 689-695 (2003)

Magnetic Raman scattering of the ordered tetrahedral spin- $\frac{1}{2}$ clusters in $\chem{Cu_2Te_2O_5}$( $\chem{Br}$ 1-x $\chem{Cl}$ x) 2 compounds

J. 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 $\chem{Cu_2Te_2O_5}$( $\chem{Br}$ 1-x $\chem{Cl}$ x) 2 compounds are analyzed in terms of a dimerized spin model for the tetrahedral $\chem{Cu}$-clusters. It is shown that the longitudinal magnetic excitation in the pure $\chem{Br}$ 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 $\chem{Br}$ is replaced by $\chem{Cl}$ 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- $\frac{1}{2}$ 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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