Elastic constants of some MAl2 single crystals

Elastic constants of single crystals of the cubic Laves phases CaAl2, YAl2, LaAl2, and GdAl2 have been measured over the temperature range 4.2–300 K. The ferromagnetic transition in GdAl2 near 170 K is evident by changes in slope in plots of the three independently measured elastic constants of GdAl2 as functions of temperature. Debye temperatures at 0 K were evaluated as 474 K for CaAl2, 484 K for YAl2, 374 K for LaAl2, 399 K for magnetically disordered GdAl2, and 406 K for magnetically ordered GdAl2. It was inferred from the data that the valence electron distributions in nonsuperconducting YAl2 and GdAl2 are much alike, but the valence electron distribution in superconducting LaAl2 is significantly different. Thus the results support a theoretical calculation indicating an admixture of 4f character into the valence bands of LaAl2.