Crystal field effects on the elastic constants of single crystals of PrAl2 and NdAl2

Measurements are reported of the sound velocity of single crystals of PrAl2 and NdAl2 between 4.2 K and 280 K. For the elastic constants is found at 280 K (in 1011N/m2):C11 = 1.382 +- 1.2%; C12 = 0.42 +- 3.6%; C44 = 0.452 +- 1.0% for PrAl2 and C11 = 1.41 +- 1.2%; C12 = 0.470 +- 3.6%; C44 = 0.429 +- 1.0% for NdAl2. Some modes of the sound velocity increase with increasing temperature over a large range above the Curie temperature. This increase is interpreted in terms of the interaction between the crystal field and the strains. (Auth.)