Magnetic field and temperature dependence of the velocity of sound in Tb.3Dy.7Fe2

Measurements of the velocity of sound in Tb.3Dy.7Fe2 as a function of magnetic field and temperature are reported. The magnetic field dependence is compared with a calculation of the change in elastic moduli of a random array of crystallites which are magnetoelastically coupled to the sound field. Comparison is also made with measured sound velocity changes with field in amorphous alloys of the R‐Fe type.