  The first- and second-order magnetoelastic coefficients of the metastable bcc
phases Co and Ni are calculated by using a combination of the phenomenological
theory of nonlinear magnetoelasticity with the ab-initio density functional
electron theory. The magnetoelastic behavior of the bcc phases is drastically
different from that of the corresponding fcc phases. The recently synthesized
bcc phase of Ni appears to be an example of a material for which third-order
magnetoelastic effects are essential.
