Magnetoelectric Effect in Piezopolymer Composites with a Weakly-Magnetostrictive Filler: The Contribution of Torsional Stresses

The magnetoelectric (ME) effect in composites consisting of a piezopolymer matrix (PVDF or akin) filled with the ferrite particles possessing weak or zero magnetostriction (barium hexaferrite, BFO or akin) is considered. A theoretical model is proposed that takes into account the contribution of the mechanical stresses arising due to magnetic torques applied to the particles on the part of external field. The model composite film is constructed as a layer of adjoined identical representative cells each of which is made of the PVDF polymer surrounding a single-domain platelet ferrite particle; the calculations are performed by finite-element method. The piezoelectric response of the model film is analyzed to find its dependence on the orientation of the particles, their positions with respect to the film boundary, and the direction of piezoelectric anisotropy of the matrix. The estimations show that, even in the case of zero magnetostriction of the ferrite, such a film is able to display the ME-effect quite comparable with that of the conventional PVDF-composites where the ME-effect is driven solely by the magnetostriction of cobalt ferrite. This result points out a way to develop efficient polymer ME composites for low-frequency applications under minimal requirements to the magnetostrictive properties of the filler.