A theory of magnetoelectric coupling with interface effects and aspect-ratio dependence in piezoelectric-piezomagnetic composites

In a piezoelectric-piezomagnetic composite, one of the most intriguing features of its characteristics is the presence of magnetoelectric coupling coefficient even though neither phase possesses such a property. This quantity is often considered to be the figure of merits, but its magnitude depends on the phase properties, connectivity, volume concentration, inclusion shape, and interfacial conditions. In this article, we develop a composite model with aligned spheroidal inclusions in the matrix to account for all these microstructural features. With a focus on the BaTiO₃-CoFe₂O₄ (BTO-CFO) system, we demonstrate how its coupling coefficients, α 33 and α 11, and voltage coefficients, α E 33 and α E 11, depend on these factors. In particular, we show that a weak interface could significantly lower the coupling effect, 1-3 composites tend to deliver a stronger α 33 while 2-2 composites a stronger α 11, and that CFO-in-BTO composites provide stronger coupling than BTO-in-CFO. We conclude by demonstrating that consideration of a weak interface is often essential to model a real system, and that experimentally measured α E 33 for CFO-in-BTO falls below the ideal value of perfect interface but can be predicted by a weak interface model. For ready applications, explicit expressions of α 33 and α 11 of fibrous composites and multilayers are also given for both perfect and imperfect interface conditions.