The magnetic properties of the interacting dimer system ${\mathrm{T}\mathrm{l}\mathrm{C}\mathrm{u}\mathrm{C}\mathrm{l}}_3$ are investigated within a bond-operator formulation. The observed field-induced staggered magnetic order perpendicular to the field is described as a Bose condensation of magnons which are linear combinations of dimer singlet and triplet modes. This technique accounts for the magnetization curve and for the field dependence of the magnon dispersion curves observed by high-field neutron scattering measurements.

• Received 2 May 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.077203