The ME effect between ferrimagnetic NFO and ferroelectric
PZT phases was demonstrated by observing the electric
field induced magnetization change. The magnetization
curve M-H curve was monitored under different external
electric fields across the PZT substrate. Due to the inverse
piezoelectric effect, the PZT substrate experiences an inplane
strain when a certain direction electric field is applied
through thickness. This in-plane strain is anisotropic in plane
due to the beam shape lengthwidth of the PZT slab, leading
to an anisotropic in-plane net stress in the PZT. This net
stress in PZT results in an effective net in-plane magnetic
field on the ferrite film through a stress mediated ME coupling
between the ferrite film and the PZT substrate, and,
therefore, magnetization change of the ferrite films due to the
inverse magnetoelastic effect. It is notable that the spin-spray
deposited NFO is isotropic in plane, thus, the ME coupling
induced magnetization change in the NFO/PZT is different
from what we recently observed for the FeGaB/PZT,28 in
which the FeGaB film has well-defined in-plane anisotropy.
Much stronger ME coupling is expected for the ME composites
with magnetic films with well-defined anisotropy.
The in-plane M-H curves were measured by applying
external electric field of 0 and 1.3 MV/m across the
thickness direction of PZT substrate, as shown in Fig. 4. An
obvious upward shift of M-H curve was observed at low
external magnetic field and the remnant magnetization
was increased by 10% when applying electric field of
1.3 MV/m. In addition, we found both M-H curves reached
the same saturation magnetization at high external magnetic
field, which indicated ME coupling reduced due to the saturated
magnetostriction at high applied magnetic field.