The elastic coupling in multiferroic materials and even more so in magnetoelectric composites plays an important role for the properties and function of these materials. In this complementary in situ X-ray scattering experiment and transmission electron microscopy study we have investigated the crystal structure and its effect on the electrically induced strain transfer at the interface of a magnetoelectric composite. These planar composites consist of a piezoelectric 0.72Pb(Mn1/3Nb2/3)O3-0.28PbTiO3 substrate and an epitaxially grown magnetostrictive CoFe2O4 layer.
Grazing incidence X-ray diffraction experiments within an in situ applied electric field reveal a surprisingly non-perfect elastic coupling of the in plane strain ε of 87%±7% in this epitaxial system. High-resolution transmission electron microscopy micrographs explain this behavior by the presence of planar defects in the CoFe2O4 film acting as trapping sites for a complete strain transfer.