Electron magnetic resonance studies of the Pr3Ga5SiO14 and Nd3Ga5SiO14 kagomé systems

We report low-temperature, high-frequency (50–800 GHz) electron magnetic resonance measurements on single crystals of the antiferromagnetic kagomé lattice compounds Nd3Ga5SiO14 and Pr3Ga5SiO14. The obtained spectra are extremely rich, displaying a large number of sharp peaks whose positions exhibit a strong systematic temperature dependence. In contrast, the spectra do not seem to follow any systematic dependence on the microwave frequency. This leads us to conclude that the observed features are quite different from conventional independent-particle electron paramagnetic resonance transitions, arising instead from collective excitations associated with finite-sized antiferromagnetically ordered clusters.