  The observation of strong magnetoelectric effects is reported in thick film
bilayers and multilayers of ferrite-lead titanate zirconate (PZT) and lanthanum
nanganite-PZT. The ferrites used in our studies included pure and zinc
substituted cobalt-, nickel- and lithium ferrites. Samples were prepared by
sintering 10-40 mm thick films obtained by tape-casting. Measurements of ME
voltage coefficients at 10-1000 Hz indicated a giant ME effect in nickel
ferrite-PZT, but a relatively weak coupling in other ferrite-PZT and
manganite-PZT systems. Multilayers prepared by hot pressing was found to show a
higher ME coefficient than sintered samples. Evidence was found for enhancement
in ME coefficients when Zn was substituted in ferrites. The Zn-assisted
increase was attributed to low anisotropy and high permeability that resulted
in favorable magneto-mechanical coupling in the composites. We analyzed the
data in terms of our recent comprehensive theory that takes into account actual
interface conditions by introducing an interface coupling parameter.
Theoretical longitudinal and transverse ME voltage coefficients for unclamped
and clamped samples are in general agreement with data. From the analysis we
inferred excellent interface coupling for nickel zinc ferrite-PZT and weak
coupling for other layered systems.
