Structural instability of ZnFe2O4-BaTiO3 magnetoelectric core-shell nanoparticle: An in situ analysis by PFM

Magnetoelectric core-shell nanoparticles (ME CSNPs) have gained significant attention for their potential applications in multifunctional devices. We investigate the electrical stability of ZnFe₂O₄-BaTiO₃ ME CSNPs (ZFO-BTO ME CSNPs) under various external bias voltages. The phase composition of the core-shell nanoparticles was determined through Rietveld refinement of X-ray diffraction data, indicating a tetragonal BaTiO₃ shell and cubic ZnFe₂O₄ core, present in a weight ratio of 63.63:35.20. Transmission electron microscopy (TEM) analysis shows that the core is composed of ZnFe₂O₄ with a diameter of 30–50 nm, surrounded by a BaTiO₃ shell with a diameter ranging from 100 to 400 nm. Piezoresponse force microscopy (PFM) results demonstrate that ZFO-BTO CSNPs exhibit a stable core-shell configuration up to 1 V, beyond which structural disintegration occurs. The instability of ZFO-BTO ME CSNPs is attributed to nonuniform interfacial strain, low ZnFe₂O₄ core magnetostriction, and a suboptimal core-to-shell thickness ratio. PFM switching studies reveal 90° domain polarization in the BaTiO₃ shell. These findings provide valuable insights into the design of novel core-shell nanocomposites with enhanced magnetoelectric coupling and structural stability.