Exploring strategies for enhancing magnetoelectric effects in piezoelectric polymer-magnetostrictive nanoparticle systems

Magnetoelectric 0-3 type nanocomposites for biomedical applications comprised of a piezoelectric polymer and homogeneously dispersed magnetostrictive nanoparticles are investigated with the aim of enhancing the electrical effects elicited by an ac magnetic field. Magnetically blocked magnetite and cobalt ferrite nanoparticles are modelled by means of the rate-equation method, and the magnetoelectric effect is calculated from the elastic and piezoelectric properties of the host polymer. A high value of the nanoparticle magnetostriction constant is shown not to be an essential prerequisite for generating a large electric signal. The magnetoelectric response is improved by adding a magnetic bias field and by varying the amplitude of the ac field, so that the nonlinear region of the magnetostrictive strain can be effectively explored and an optimum working point assuring the best magnetoelectric performance can be defined for each material. The electric response of the nanocomposites is significantly enhanced by collinear instead of randomly directed easy axes of the dispersed nanoparticles; in the collinear case, an analytic expression of the magnetoelectric effect is derived.