The physics of magnetoelectric composites

This paper gives an overview about the basic ideas of magnetoelectric materials. Up to now single-phase materials show the magnetoelectric effect only below room temperature. Mixing a magnetostrictive with a piezoelectric component is a way to overcome this limitation. This delivers a composite which can exhibit a magnetoelectric effect even at room temperature and higher. Possible candidates for these composites (piezoelectric as well as magnetostrictive) are shown, examples from literature and own results are given. The most important coupling mechanism (magnetization, magnetostriction, local stress, charge) between the magnetostrictive and the piezoelectric phase are discussed. Hints for a direct coupling between the electric polarization and the magnetization are also presented. Different measurement methods for determining the magnetoelectric coefficient are discussed. Representative results as obtained on a technical useful composite between 50% Co-Ferrite+50% BaTiO₃ are given. The behavior of a simple “mixed” structure with that of a “core-shell” structure is compared. The later gives a 20-times larger magnetoelectric coefficient.