Low-energy excitations in the rare earth kagome spin system Pr${}_3$Ga${}_5$SiO${}_{14}$ (PGS) have been investigated using high-field electron spin resonance (ESR) techniques. Previous work has shown that PGS does not exhibit long-range magnetic order at temperatures down to 30 mK. The present low-temperature (1.3–20 K) field-scan measurements, made on a single crystal sample in applied fields up to 30 T and for several microwave frequencies, give a series of temperature-dependent absorption peaks that are very different to conventional ESR spectra. The observed response is interpreted in terms of discrete spin-wave excitations in antiferromagnetically correlated spin clusters. We present a theoretical model which, in the limit of small magnetic frustration effects, qualitatively describes the microwave-induced transitions.

• Received 25 June 2013

DOI:https://doi.org/10.1103/PhysRevB.88.094414