Prediction of tunable magnetoelectric properties in compositionally graded ferroelectric/ferromagnetic laminated nanocomposites

摘要

The advent of modern thin-film deposition approaches has ushered in a new era of designed materials with well-controlled composition distributions, e.g., compositionally graded ferroelectric (CGFE) thin films, and thereby, it is readily accessible CGFE/FM (ferromagnetic) multilayer thin films. Being recognized this emerging class of materials, in this study, we develop a phase-field model based on the Ginzburg-Landau theory that takes into account the gradient of ferroelectric (FE) compositions in order to predict material properties of CGFE/FM thin films. The developed phase-field model is applied to investigate the effect of the FE composition gradient on magnetoelectric (ME) coupling of graded Pb_((1-x))Sr_xTiO_3/CoFe_2O_4 laminated nanocomposites. Two types of composition gradients are considered: inward (O-type) and outward (X-type) gradients. Unusual polarization domain structures with curved domain walls are formed in CGFE layers, which are governed by the composition gradients and distinct from typical stripe domains in homogeneous counterparts. As a result, the ME effect is strongly dependent on the composition gradient. Particularly, the ME coupling in the O-type nanocomposites increases with the increasing composition gradient, while it decreases in the X-type ones. The dependence of ME coupling on the composition gradient originates from the distinguishable energy distributions in O-type and X-type nanocomposites. This work, therefore, provides a strategy to design the ME effect via the configuration of the composition gradient.