Magnetoelectric effects in ferrite-lead zirconate titanate layered composites: The influence of zinc substitution in ferrites

The observation of strong magnetoelectric (ME) coupling is reported in zinc-substituted layered composites of ferrites and lead zirconate titanate (PZT). Multilayer samples contained cobalt zinc ferrite Co1-xZnxFe2O4 (CZFO) (x=0-0.6) or nickel zinc ferrite Ni1-xZnxFe2O4 (NZFO) (x=0-0.5) and were prepared by laminating and sintering ferrite and PZT thick films obtained by tape casting. The ME voltage coefficient alpha(E) was measured for transverse and longitudinal field orientations for frequencies 10-1000 Hz. A substantial enhancement in alpha(E) is observed with the substitution of Zn. The largest increase, by about 500%, is observed in CZFO-PZT and the smallest increase of 60% is measured for NZFO-PZT. As the Zn concentration is increased, alpha(E) increases and shows a maximum for x=0.2-0.4, depending on the ferrite. The data is analyzed based on a theoretical model for a ferrite-PZT bilayer, taking into consideration less than ideal coupling at the interface. The interface coupling parameter k is quite small for CZFO-PZT; it increases from 0 to 0.6 as Zn concentration is increased from 0% to 40%. Composites of NZFO-PZT, however, have a near perfect interface coupling. The Zn-assisted enhancement in the ME coefficient is discussed in terms of joule magnetostriction, initial permeability, and magnetomechanical coupling for the ferrites.