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 ${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ (CZFO) $(x=0--0.6)$ or nickel zinc ferrite ${\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ (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 ${\ensuremath{\alpha}}_{E}$ was measured for transverse and longitudinal field orientations for frequencies 10--1000 Hz. A substantial enhancement in ${\ensuremath{\alpha}}_{E}$ 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, ${\ensuremath{\alpha}}_{E}$ 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.