Temperature-dependent magnetoelectric response of lead-free Na_0.4K_0.1Bi_0.5TiO₃/NiFe₂O₄-laminated composites

This study investigates the temperature-dependent quasi-static magnetoelectric (ME) response (αE) of electrically poled lead-free Na_0.4K_0.1Bi_0.5TiO₃–NiFe₂O₄ (NKBT–NFO)-laminated composites. The aim is to understand the temperature stability of ME-based sensors and devices. The relaxor ferroelectric nature of NKBT is confirmed through impedance and polarization–electric (PE) hysteresis loop studies, with a depolarization temperature (T _d) of approximately 110 °C. Heating causes a decrease and disappearance of planar electromechanical coupling (K _p), charge coefficient (d ₃₁), and remnant polarization (P _r) above T _d. The temperature rise to 125 °C also leads to a reduction in magnetostriction (λ) and magnetostriction coefficient (q = dλ/dH) of NFO by approximately 33% and 25%, respectively. At room temperature, the bilayer and trilayer configurations exhibit maximum ME responses of approximately 33 mV/cm·Oe and 80 mV/cm·Oe, respectively, under low magnetic field conditions (H ∼ 300–450 Oe). The ME response of NKBT/NFO is highly sensitive to temperature, decreasing with heating in accordance with the individual temperature-dependent properties of NKBT and NFO. This study demonstrates a temperature window for the effective utilization of NKBT/NFO-based laminated composite ME devices.