Magnetic Field-Induced Polarization Rotation in Strain-Engineered 0.94(Na<inf>0.5</inf>Bi<inf>0.5</inf>TiO<inf>3</inf>)-0.06BaTiO<inf>3</inf>/CoFe<inf>2</inf>O<inf>4</inf> Magnetoelectric Nanocomposites for Energy Harvesting

The study focuses on the polarization dynamics of the ferroelectric phase under an external magnetic field in a trilayered magnetoelectric (ME) composite of 0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3 (NBT-BT)/CoFe2O4(CFO)/NBT-BT. With the estimation of gradient size of the strain across the interface, the thin films with varying top layer (NBT-BT) thicknesses were fabricated. The piezoelectric displacement curves revealed the linear characteristics for the 30 nm NBT-BT ME composite due to the presence of dominant interfacial strain. Time-resolved polarization switching studies confirmed the role of interfacial strain on the time scale of polarization switching of the ferroelectric phase. Magnetic field-assisted piezoresponse force microscopy studies confirmed the presence of nonlinear contribution like polarization rotation in the 100 nm NBT-BT ME composite. The interfacial strain was found to operate in a way that imposes constraints on the polarization rotation in a spatial region of ∼20-30 nm away from the interface. However, at a spatial region >30 nm, the interfacial strain was found to supplement the field-induced strain and assisted the polarization rotation to happen. The spatial-dependent behavioral analysis of the interface strain on the polarization dynamics will help in using the ME composite for targeted device applications such as actuators or energy harvesters.