Abstract
The prediction of magnetoelectric (ME) coupling in nano-scaled multiferroic composites is significant for nano-devices. In this paper, we propose a nonlinear multi-field coupling model for ME effect in layered multiferroic nanocomposites based on the surface stress model, strain gradient theory and nonlinear magneto-elastic-thermal coupling constitutive relation. With this novel model, the influence of external fields on strain gradient and flexoelectricity is discussed for the first time. Meanwhile, a comprehensive investigation on the influence of size-dependent parameters and multi-field conditions on ME performance is made. The numerical results show that ME coupling is remarkably size-dependent as the thickness of the composites reduces to nanoscale. Especially, the ME coefficient is enhanced by either surface effect or flexoelectricity. The strain gradient in composites at the nano-scale is significant and influenced by the external stimuli at different levels via the change in materials’ properties. More importantly, due to the nonlinear multi-field coupling behavior of ferromagnetic materials, appropriate compressive stress and temperature may improve the value of ME coefficient and reduce the required magnetic field. This paper provides a theoretical basis to analyze and evaluate multi-field coupling characteristics of nanostructure-based ME devices.
Highlights
Multiferroic materials possess two or more unique ferroic properties simultaneously, such as ferromagnetism, ferroelectricity and ferroelasticity [1]
A number of models considering both surface piezoelectricity and piezomagnetic effect have been developed for investigating the nano-ME system [15,16], in which flexoelectricity induced by a strain gradient or an inhomogeneous deformation [17,18] in multiferroic composites is ignored
After an extensive literature review, the authors find that experimental data on nonlinear ME coupling of layered multiferroic nanocomposites under stress or thermal loading is relatively scarce
Summary
Multiferroic materials possess two or more unique ferroic properties simultaneously, such as ferromagnetism, ferroelectricity and ferroelasticity [1]. A number of models considering both surface piezoelectricity and piezomagnetic effect have been developed for investigating the nano-ME system [15,16], in which flexoelectricity induced by a strain gradient or an inhomogeneous deformation [17,18] in multiferroic composites is ignored. As for the multiferroic composites with nano-scale thickness, the applied external stimuli (e.g., magnetic field, pre-stress and temperature) influence the magnetostriction and magnetization of FM phase, so they may have effects on strain gradient as well as the materials’ properties of FM materials. It is urgent and necessary to establish a theoretical model to analyze the size-dependent behavior and nonlinear multi-field coupling properties of multiferroic nanocomposites. The multi-field coupling characteristics of multiferroic composites are analyzed for the improvement of ME performance
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