Sound-Wave Anomalies in UCuGe

The hexagonal compound UCuGe is an antiferromagnet (AFM) with T_N = 48 K. In this study we report on results of sound-velocity and sound-attenuation measurements performed on a single crystal of UCuGe at different frequencies, in the temperature range 1.3 K > T > 295 K, and in a magnetic fields up to 18 T applied along the c axis (hard axis). The temperature dependences of the sound velocity and attenuation display a pronounced anomaly at T_N suggesting a large magnetoelastic coupling. A double-peak structure is observed in the sound velocity at T_N which might be due to frustration. In the paramagnetic state (T > T_N), both acoustic characteristics show large frequency-dependent changes revealing the presence of unusual relaxation processes. No hysteresis in the field dependence of the sound velocity in the AFM state is observed confirming that the compound UCuGe has a single-domain state.