Unlocking Strong Zero-Bias Magnetoelectric Effects in Bilayers of PZT and Self-Biased Hexagonal Ferrite–Spinel Ferrite Composites

Ferromagnetic–ferroelectric bilayers capable of strong zero-bias magnetoelectric (ME) coupling are critical for device miniaturization. Here, we report a self-biased ME response achieved in a bilayer structure consisting of lead zirconate titanate (PZT) and a dual-phase ferromagnetic composite. The composite consisted of hard barium hexaferrite (BaFe12O19) (BaM), which provides a high built-in magnetocrystalline anisotropy field, and soft nickel zinc spinel ferrite (Ni0.8 Zn0.2 Fe2O4) (NZFO) to ensure high magnetostriction compliance. Samples of (100 − x) wt.% BaM − x wt.% NZFO (BNZx) were synthesized via conventional solid-state sintering, with phase purity confirmed by X-ray diffraction. Magnetic characterization revealed substantial in-plane anisotropy fields (HA) ranging from 4.8 kOe to 8.3 kOe and a high saturation magnetostriction λ11 = −25 ppm. The ME voltage coefficient (MEVC) of the bilayers increased with higher spinel content, peaking at x = 90. Under zero external DC bias field, the BNZ90-PZT bilayer showed a low-frequency (=100 Hz) MEVC of 114 mV/cm Oe and a resonant (10.6 kHz) MEVC of 3.6 V/cm Oe. This strong self-biased coupling is driven by the BaM-provided internal magnetic flux, eliminating the need for external biasing elements and offering a practical framework for compact, bias-free sensors and energy harvesters.