We have performed ESR measurements on the S = 1/2 double-spin-chain systems KCuCl3 and TlCuCl3 using single crystals. The ground states of these compounds are spin singlet and there are finite gaps in their excitation spectra. The temperature dependence of the paramagnetic resonance intensity is similar to that of susceptibility. The direct transition from the singlet ground state to the excited triplet state is observed for both compounds.
- Dzyaloshinsky-Moriya interaction
- Electron-spin resonance
- Energy gap
- Singlet ground state