1. F. E. Pinkerton, T. W. Capehart, J. F. Herbst, E. G. Brewer, and C. B. Murphy, Appl. Phys. Lett. (in press).
2. L. D. Landau and E. M. Lifshitz, Theory of Elasticity, Course of Theoretical Physics Vol. 7 (Pergamon, Oxford, 1970).
3. L. D. Landau and E. M. Lifshitz, Theory of Elasticity, Course of Theoretical Physics Vol. 7 (Pergamon, Oxford, 1970), p. 24.
4. Since we use a cube as the building block for the composite while the magnetostrictor is spherical, Eq. (10) and Eq. (11) do not strictly apply in the f→1 limit (magnetostrictive material only). In particular, Eq. (11) yields λ∗(f=1)=0.8933 for σ2=0.33.
5. We extrapolate a saturation magnetostriction of −1555 ppm for our SmFe2 ingot, identical to the literature value of −1560 ppm [A. E. Clark, in Ferromagnetic Materials, edited by E. P. Wohlfarth (North-Holland, Amsterdam, 1980), Vol. 1, p. 542]. Since all the composites are characterized by some porosity, we used the magnetostriction of the hot-pressed SmFe2-only reference sample in obtaining the experimental λ∗ ratios in Fig. 2. Compensating λS(1)=−964 ppm of the reference for porosity (using the measured density relative to the SmFe2 ingot density) yields an estimate of −1450 ppm for its magnetostriction at full density. Such a simple density correction is clearly approximate at best, and we chose not to employ it. Nevertheless, imposing that correction on all samples produces no significant changes in the λ∗ ratios.