Neutron inelastic scattering investigation of the magnetic excitations in Cu2Te2O5X2 (X=Br,Cl)

Neutron inelastic scattering investigations have been performed on the spin tetrahedral system Cu2Te2O5X2 (X=Cl, Br). We report the observation of magnetic excitations with a dispersive component in both compounds, associated with the three-dimensional incommensurate magnetic order that develops below T-N(Cl)=18.2 K and T-N(Br)=11.4 K. The excitation in Cu2Te2O5Cl2 softens as the temperature approaches T-N(Cl), leaving diffuse quasi-elastic scattering above the transition temperature. In the bromide, the excitations are present well above T-N(Br), which might be attributed to the presence of a degree of low dimensional correlations above T-N(Br) in this compound