Effect of porosity on the effective magnetostriction of polycrystals

Explicit relations for determining the effective magnetostriction of polycrystals with cubic magnetostrictive crystallites and pores are derived based on the Green’s function technique. For comparison, two extreme approximations-the Reuss and Voigt-type approximations-are also given. To illustrate the technique, the influence of porosity on the effective saturation magnetostriction of common magnetostrictive metals (Fe and Ni), giant magnetostrictive alloy terfenol-D, and Fe–Co spinel are illustrated. The theoretical estimates show an interesting nonmonotonic concentration dependence of magnetostrictive behavior of the polycrystals with such magnetostrictive microcrystallites as Ni and Fe–Co spinel, whose magnetic easy axes are 〈100〉 axes rather than 〈111〉 axes.