Giant Direct Magnetoelectric Effect in Nanocomposite CoFe₂O₄:PVDF-TrFE Thin Films

Polymer-based magnetoelectric (ME) materials are at the forefront of modern materials science. They have immense potential in a wide range of technological applications, including sensors, energy harvesters, and advanced memory and logic devices. Thus, the combination of magnetostrictive (MS) nanomaterials with lightweight flexible piezoelectric (PE) polymers enables the development of multifunctional systems suitable for versatile applications in the mechanical, electrical, and magnetic domains. Here, a novel three-step fabrication process was employed to create a uniquely structured MS/PE nanocomposite. First, a vertically aligned nanocomposite (VAN) thin film of MS CoFe₂O₄ (CFO) nanopillars, self-assembled in a benign MgO matrix phase, was grown. Then, wet chemical etching of the benign MgO phase was undertaken. Finally, the CFO nanopillars were coated with a ferroelectric (FE) polymer. The high interfacial area, highly crystalline nanocomposite system enabled efficient strain-mediated coupling between the magnetic and electric order parameters. Thus, a significantly enhanced magnetoelectric coefficient ( ${\alpha }_{33}^{DME}$ ) of 10 ± 1 V cm^{- 1}Oe^{- 1} was achieved at room temperature, nearly two orders of magnitude higher than similar composite thin film systems previously reported. Our method offers a simple, versatile, and scalable approach to fabricating very high-performance ME thin film devices.