Structural and magnetic dimers in the spin-gapped system CuTe2O5

We investigate the magnetic properties of the system $\mathrm{Cu}{\mathrm{Te}}_{2}{\mathrm{O}}_{5}$ by susceptibility and electron spin resonance (ESR) measurements. The anisotropy of the effective $g$ factors and the ESR linewidth indicates that the anticipated structural dimer does not correspond to the singlet-forming magnetic dimer. Moreover, the spin susceptibility of $\mathrm{Cu}{\mathrm{Te}}_{2}{\mathrm{O}}_{5}$ can only be described by taking into account interdimer interactions of the same order of magnitude than the intradimer coupling. Analyzing the exchange couplings in the system we identify the strongest magnetic coupling between two Cu ions to be mediated by a super-superexchange interaction via a bridging Te ligand, while the superexchange coupling between the Cu ions of the structural dimer only results in the second strongest coupling.