Multiferroic magnetoelectric constitutes two phases, that is, the piezoelectric and the magnetostrictive phases. Just like any other composite formed from a combination of one or more materials with distinct individual properties to achieve a desired unique property, these magnetoelectric composites are equally similar. They too exhibit properties that cannot be produced by a single-phase acting along hence explaining their intensive applications in various areas such as structural composites as well as devices like sensors, gyrators, microwaves and energy harvesters.
In most cases, the physical and mechanical properties of most nanomaterials are determined by their sizes. However, the nanomaterials size properties are believed to be affected by other external factors. This may, in turn, affect the functionality of these materials, as seen in the case of multiferroic magnetoelectric (ME) composites where their sizes are mainly affected by the surface effects. This is as a result of high surface to volume ratios of such materials.
Therefore, the need to predict the surface effects of ME and other nanocomposites materials will ensure their proper design and thus achieving greater performance as far as their functionalities are concerned. Although various theoretical and model techniques have been used to analyze the surface structures, there are still challenges as they involve complex computations and simulations. However, the use of models that involves different magnetostrictive materials and the effects of the characteristics of ME nanostructures has been regarded as a possible solution.
Dr. Yang Shi form the School of Mechano-Electronic Engineering at Xidian University in China, developed a nonlinear theoretical model for multiferroic magnetoelectric nanocomposites. The model uses different magnetostrictive materials. The technique takes into considerations the nonlinear characteristics of the material and the surface effects. This work has been henceforth published in the journal, Composite Structures.
Dr. Shi used the available Gurtin-Murdoch theory to establish his theoretical model, derived and deduced the ME effects through the use of surface effects and flexural strains. Finally, he numerically analysed the factors that influence the ME coefficient.
From the experiment, Shi discovered that the ME coupling of the composites can be significantly improve by the surface effects especially those with nano-scale thickness.
According to Dr. Shi, the ME coupling is inversely proportional to the thickness of the nanostructures. That is, increase in the thickness leads to a diminishing ME coefficient because of the decreasing surface effects. Other external factors such as a combination of the magnetic loading and the pre-stress loading influence the characteristics of the magneto-mechanical nanostructures. For example, when an increase is observed in the compressive pre-stress irrespective of the magnitude, there is a corresponding decrease in the ME peak to peak coefficient and increase in the magnetic field. The same responses were observed in the ME characteristics of a nanostructure when subjected to a significantly strong magnetic field.
The research work, therefore, provides a basic understanding of the behavioral aspects of a magneto-mechanical coupling, giving guidance on the surface effect prediction and thus enables the design of more effective ME nano-devices.
Shi, Y. (2018). Modeling of nonlinear magnetoelectric coupling in layered magnetoelectric nanocomposites with surface effect. Composite Structures, 185, 474-482.
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