Dzyaloshinsky-Moriya interaction and long lifetime of the spin state in the Cu₃ triangular spin cluster by inelastic neutron scattering measurements

Inelastic neutron scattering (INS) experiments have been performed on the Cu₃ triangular molecular nanomagnet using powder samples. In the medium resolution INS experiment, two peaks were observed at ω=0.5 and 0.6 meV, whereas an additional excitation peak was detected at very low energy ω=0.1 meV in the higher resolution experiment. A model Hamiltonian and its optimum interaction parameters were determined from the observed peak position, width, and intensity. A key ingredient of the model Hamiltonian is Dzyaloshinsky-Moriya interactions as suggested in the earlier reports, which is now directly evidenced by the observation of the 0.1-meV peak, corresponding indeed to a splitting of ground-state quartet into two doublets. Temperature dependences of integrated intensity of the 0.5- and 0.6-meV peaks are well reproduced by the Boltzmann distribution function up to 10 K, above which a small deviation was detected. Nevertheless, the inelastic peaks were visible even at very high temperatures as 50 K, indicating extraordinary weak coupling between spins and lattice vibrations (or any other perturbations) compared to the other known molecular nanomagnets.