Magneto-acoustic study of single crystalline UCu_0.95Ge

We present results of a magneto-acoustic study on a UCu_0.95Ge single crystal. This compound exhibits antiferromagnetic ordering at 48 K and shows a first-order metamagnetic phase transition at 38 T to a spin-polarized state, i.e., when the magnetic field is applied along the c direction a sharp jump in the magnetization appears. The sound velocity and sound attenuation demonstrate pronounced anomalies in the vicinity of both magnetic phase transitions proving the important role of magneto-elastic interactions in the physics of this actinide compound. Above T_N, the acoustic characteristics show some unusual frequency-dependent features which presumably can be related to the dynamics of Cu vacancies in UCu_0.95Ge. Our results are discussed in frame of a phenomenological model, which describes qualitatively the main experimental observations.