  We report the use of high magnetomechanical coupling ferrites in
magnetoelectric (ME) layered composites. Bilayer samples combining $(Ni_{0.973}
Co_{0.027})_{1-x} Zn_x Fe_2 O_4$ ferrites ($x = 0-0.5$) synthesized by non
conventional reactive Spark Plasma Sintering and commercial lead zirconate
titanate (PZT) were characterized in term of ME voltage coefficients measured
at sub-resonant frequency. Strong ME effects are obtained and we show that an
annealing at 1000$^\circ$C and a quenching in air improve the piezomagnetic
behavior of Zn-rich compositions. A theoretical model that predicts the ME
behavior was developed, focusing our work on the demagnetizing effects in the
transversal mode as well as the longitudinal mode. The model shows that: (i)
high ME coefficients are obtained when ferrites with high magnetomechanical
coupling are used in bilayer ME composites, (ii) the ME behavior in transversal
and longitudinal modes is quite similar, and differences in the shapes of the
ME curves are mainly due the demagnetizing effects, (iii) in the transversal
mode, the magnetic field penetration depends on the ferrite layer thickness and
the ME coefficient is affected accordingly. The two later points are confirmed
by measurements on ME samples and calculations. Performances of the ME
composites made with high magnetomechanical coupling ferrites are compared to
those obtained using Terfenol-D materials in the same conditions of size,
shape, and volume ratio. It appears that a ferrite with an optimized
composition has performances comparable to those obtained with Terfenol-D
material. Nevertheless, the fabrication processes of ferrites are quite
simpler. Finally, a ferrite/PZT based ME composite was used as a current
sensor.
