Nanoscale Polarization Switching and Magneto-Piezoelectric Coupling in MgFe₂O₄-PVDF-HFP Nanocomposites for Low-Field Magnetic Energy Harvesting and Self-Powered IoT Microsystems

Abstract

Magneto-piezoelectric technology has emerged as a promising multifunctional platform for hybrid and self-powered sensing systems, wearable electronics, and low-power Internet-of-Things (IoT) applications by harvesting both mechanical vibrations and stray magnetic fields. In this study, we demonstrate a compositionally optimized magneto-piezoelectric composite where the calculated incorporation of MgFe 2 O 4 nanofillers into electroactive PVDF-HFP matrix enables efficient synchronization between magnetic stimulus, mechanical deformation and piezoelectric charge generation. The optimal composition with superior β-phase nucleation, MF-3, shows the highest maximum polarization of 7.3 nC/cm 2 with a recoverable energy density of 0.67 µJ/cm 3 at a low electric field of 220 V/m. Nanoscale Switching Spectroscopy-Piezoelectric Force Microscopy measurements reveal a displacement of 1.8 nm and a near-complete phase reversal of 170°, confirming a reversible polarization switching at the domain level. The prototype magneto-piezoelectric nanogenerator fabricated with MF-3 film generates a high peak-to-peak voltage of 97.5 V under dynamic mechanical excitation via human finger tapping motion, higher than widely studied spinel fillers. Most notably, the MF-3 composite exhibits a distinct magneto-piezoelectric response, generating a voltage of ~ 40 mV when exposed to a low magnetic field of 320 µT, originating from the coupling of the magnetic and piezoelectric phases that efficiently transfers the magnetic strain as a stimulus to the electroactive composite. The practical viability of the multimodal coupling is further demonstrated through charging of a 1 µF capacitor to 4.5 V under 2.5 seconds, optimal power transfer at 30 MΩ external resistance and powering up of multiple LEDs under tactile activation through repetitive finger tapping. This study not only unveils a highly effective design for harvesting energy from stray magnetic fields but also highlights the transformative potential of magneto-piezoelectric technology as an essential multifunctional strategy in next-generation technological advancements.