We have employed Brillouin scattering to investigate elastic-wave velocities as a function of temperature in Dy thin films and in bulk Dy. The single-crystal films were synthesized by molecular-beam epitaxy to ensure high crystalline and interfacial quality. Surface (Rayleigh) and guided-wave (Lamb) modes were probed by the Brillouin technique through the surface ripple-coupling mechanism. Results taken near room temperature in the paramagnetic phase agree very well with a layered-elastic model in which the materials of the samples are represented by elastic behavior using bulk single-crystal elastic data from the literature. At lower temperatures anomalies were found for samples with the thinner Dy layers: Measured wave velocities differed by up to 2% from the model predictions, and the ratio of Lamb-to-Rayleigh intensities was twice the predicted value. The anomalies coincide with the ferromagnetic transitions of the films, and they are believed to originate from coupling between the phonons and the magnetic system in the near-surface region probed by the Brillouin scattering.

• Received 20 June 1994

DOI:https://doi.org/10.1103/PhysRevB.50.18497