Magnetic Field-Induced Polarization Rotation in Strain-Engineered 0.94(Na_0.5Bi_0.5TiO₃)-0.06BaTiO₃/CoFe₂O₄ 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(Na 0.5 Bi 0.5 TiO 3 )-0.06BaTiO 3 (NBT-BT)/CoFe 2 O 4 (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.