Abstract. -Raman light-scattering experiments in the antiferromagnetic phase of the Cu2Te2O5(Br1−xClx)2 compounds are analyzed in terms of a dimerized spin model for the tetrahedral Cu-clusters. It is shown that the longitudinal magnetic excitation in the pure Br system hybridizes with a localized singlet excitation due to the presence of a DzyaloshinskiiMoriya anisotropy term. The drastic change of the magnetic scattering intensities observed when a proportion of Br is replaced by 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-1 2 order perpendicular to each other, when the composition x is larger than about 0.25.The compounds Cu 2 Te 2 O 5 Br 2 and Cu 2 Te 2 O 5 Cl 2 are spin-1 2 Cu-systems with coupled spin tetrahedra. The tetragonal P 4 crystal structure of the two compounds and the susceptibility measurements are presented in ref. [1]. While the high-temperature susceptibility approaches that of uncoupled spins, at low temperatures the susceptibility is reduced and goes through a maximum at, respectively, 30 and 23 K. The maximum indicates that the 2 4 spin-1 2 states of the Cu-ions in the (distorted) tetrahedral clusters are dimerized so to create a singlet ground state separated from the excited states by a gap of about 40 K. Both the susceptibility and the heat capacity measurements clearly indicate a transition to an ordered phase at a temperature, 11.4 K in the Br and 18.2 K in the Cl system [2,3], well below that of the maximum. Some of the bulk properties and the Raman-scattering results of the Br compound have been analyzed successfully by Gros et al. [4] in terms of a dimerized model for the four Cu spins of one tetrahedron, as determined by the following Hamiltonian:J 1 and J 2 are both positive. Defining the ratio r = J 2 /J 1 then the energy differences between the singlet ground state |s 1 and the excited states are: 2(1 − r)J 1 to a singlet |s 2 , J 1 to a within the mean-field (MF) approximation, i.e., the order parameter is one where the spins on each of the pairs 1-2 and 3-4 are parallel, but antiparallel with respect to the other pair of spins. This ordering takes full advantage of the J 1 -interaction on the expense of the J 2 -interaction. In the model of Gros et al. [4] for the Br compound r = 0.66 is smaller than 1, and the system is close to quantum criticality with a coupling parameter J c = 0.85J 1 , only 13% larger than the critical value J (qc) c = 0.75J 1 . The model was investigated analytically neglecting the modifications due to higher lying levels. The high-temperature susceptibility is accounted for using J 1 = 47.7 K, the Néel temperature increases with an applied field, and the frequency of the longitudinal magnetic excitation in the ordered phase is estimated to be close to that observed by Raman spectroscopy. Here we shall present a complete MF analysis, which includes the calculation of the susceptibility and the bulk magnetization in the ordered ...