Нефарадеевское магнитоэлектричество в контексте мезомеханики

Abstract

The paper outlines the physical basis of magnetoelectric conversion by means of the piezoelectric effect. The whole class of materials capable of such conversion is termed as multiferroics. An important group of those make composite media in which the ferromagnetic (or ferrimagnetic) and piezoelectric components dwell in close contact. The magnetic field, acting on the ferromagnet arises internal mechanical stresses via it, which are perceived by the other phase of the composite and launches the piezoelectric effect in it, i.e. makes the sample a source of potential difference. Whereas the ferromagnetic phase is always a solid substance, the piezophase can be not only a solid but also a polymer, and this expands considerably the application prospects of such convertors. Fundamental analysis shows that in a polymeric composite, ferromagnet particles under the action of an external field excite the piezoeffect in two ways simultaneously: through magnetostriction (change of the particle shape) and through a mechanical displacement of the particle body. Although these two methods are, in principle, independent, in a ferrite-polymer composite they always coexist, and under a given set of conditions their joint action might either enhance or reduce the conversion ef ficiency. This general conclusion is illustrated by the results of numerical modelling of the magnetoelectric effect in a composite film whose content mimics one of the currently best known polymer multiferroics: the dispersion of cobalt ferrite particles in a matrix of polyvinylidene fluoride (CFO-PVDF).