Magnetostrictive strain (${\epsilon }_{ij}^{\mathrm{mag}}$)

Magnetostrictive strain is the preferred strain associated with a specified magnetic state relative to a stated reference. The measured strain also depends on mechanical constraints.

Volume magnetostriction is the relative volume change associated with a magnetic-state change. To first order it is the trace of the magnetostrictive strain. Zero trace is an additional restriction, not a consequence of isotropy alone.

In the saturated isotropic magnetostrictive strain convention, saturation magnetostriction is the longitudinal relative length change from a random-domain reference to alignment. A parallel-to-perpendicular length difference instead equals $3{\lambda }_s/2$ in that model.