Significant enhancement of resonance magnetoelectric coupling in miniaturized lead-free NiFe₂O₄–BaTiO₃ multilayers

With increasing demands toward device miniaturization, Pb-free magnetoelectric laminates (MELs) with a small lateral dimension of ∼3 × 3 mm² have been synthesized by the tape-casting method. The MELs are composed of alternating layers of magnetostrictive NiFe₂O₄ and piezoelectric BaTiO₃ with a uniform single layer thickness of t = 50 and 15 μm, respectively. Both laminates exhibit much larger longitudinal ME voltage coefficient α_E33 than the transverse ME voltage coefficient α_E31 at both off-resonant and resonant frequencies, which is attributed to the preferential easy-plane alignment of the magnetic moments. Furthermore, enhancement in α_E33 by more than 5 times has been achieved upon decreasing t from 50 to 15 μm in both resonance and off-resonance conditions. The enhanced α_E33 values indicate that nearly ideal interface coupling between the ferromagnetic and piezoelectric layers is realized in the miniaturized, thinner MEL, pointing to practical application potential towards developing mass-produced, low-cost ME devices.