Wrinkles of magnetoelectric composite thin films bonded on compliant buffer-layers

Laminated magnetoelectric (LME) thin films have the ability of conversion between electric and magnetic energies. However, when coated on stiff substrates, their magnetoelectric (ME) effect will be suppressed evidently due to the clamping effect of substrates. In order to reduce the clamping effect, a compliant buffer layer method is proposed in this paper which can help in inducing wrinkles of LME thin films and effectively enhance the ME effect of clamped ones. A LME wrinkling model which is a combination of LME plate theory and energy analysis method is proposed to predict the wrinkling behaviours of LME thin films bonded on compliant buffer-layers with finite thickness. The theoretical results show that the wrinkled state is one of necessary conditions of ME effect of such LME thin film/buffer-layer/substrate system and the ME effect of this system can be evidently influenced by several factors: the pre-strain in the laminated thin film, the thickness and stiffness of buffer layer. Finite element method (FEM) simulations are also conducted to verify the proposed model. Both theoretical and numerical results show that the thin films bonded on more compliant or thicker buffer layer have better ME effect, and the compressive pre-strain in LME thin films can also help in inducing wrinkles and enhancing the ME effect.