Magnetic excitations in the diamond spin system Cu₃(CO₃)₂(OH)₂ probed by ESR

We report systematic tunable-frequency electron spin resonance (ESR) studies of the natural mineral azurite Cu₃(CO₃)₂(OH)₂. This material has a diamond spin-chain structure and exhibits unusual magnetic properties (including a magnetization plateau). ESR experiments have been done at frequencies from 50 to 1000 GHz in magnetic fields up to 51 T. The observed frequency-field dependence of the magnetic excitations clearly indicates the important role of magnetic frustrations in this material, which can be suppressed by high magnetic fields. Our findings are discussed in connection with results of inelastic neutron-scattering experiments.