The elastic constants of MnAs

The tensor of elastic constants of MnAs in the ferromagnetic and paramagnetic states is evaluated from bending vibrations of straight and helical MnAs whiskers. The isotropic compressibility, predicted by the Bean-Rodbell model to be 4.6 × 10−12 dyn−1 cm2 and the same in both phases, is found experimentally to be (4.3 ± 1.0) × 10−12 dyn−1 cm2 in the paramagnetic state, changing by −0.6 × 10−12 dyn−1 cm2 at the first order phase transition. However, the data in the ferromagnetic state include magnetostrictive effects. Observation of the ΔE-effect shows that the magnetostriction softens the lattice appreciably and tends to minimize the difference in elastic constants between the two states.