Spin-cluster excitations in the rare-earth kagome system Nd3Ga5SiO14

Spin-cluster excitations induced by microwave radiation have been detected as a function of an applied magnetic field in the rare-earth kagome system Nd3Ga5SiO14. The results are interpreted using a Heisenberg model which allows for anisotropic exchange interactions between neighboring spins. At a microwave frequency of 120 GHz the conventional independent-ion electron spin resonance (ESR) spectrum, due to Zeeman splitting of the ground state Kramers doublet, is not observed at low temperatures. Instead, a large number of resonances are seen that are shifted from the conventional ESR position. These resonances persist to temperatures well above 20 K with similar behavior found at 230 GHz. The observations are consistent with the excitation of spin waves in short-range antiferromagnetically correlated spin loops or clusters and are similar to the ESR spectral features seen previously in the Pr3Ga5SiO14 kagome system. Upon increasing the temperature and/or the microwave frequency, a broad Zeeman resonance does eventually emerge at the predicted ground state doublet resonance field.