Giant magnetoelectric effect in sintered multilayered composite structures
Rashed A. Islam,
1
Yong Ni,
2
Armen G. Khachaturyan,
2
and Shashank Priya
3,a͒
1
Department of Materials Science and Engineering, UT Arlington, Arlington, Texas 76019, USA
2
Department of Materials Science and Engineering, Rutgers University, Piscataway, New Jersey 08854,
USA
3
Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA
͑Received 7 May 2008; accepted 11 June 2008; published online 19 August 2008͒
Trilayer composites consisting of 0.9Pb͑Zr
0.52
Ti
0.48
͒O
3
–0.1Pb͑Zn
1/3
Nb
2/3
͒O
3
͑0.9 PZT-0.1 PZN͒
and Ni
0.6
Cu
0.2
Zn
0.2
Fe
2
O
4
͑NCZF͒ in the configuration NCZF-͑0.9 PZT-0.1 PZN͒-NCZF were
synthesized using pressure assisted sintering. Composites with optimized magnetostrictive to
piezoelectric thickness ratio showed a high magnetoelectric ͑ME͒ coefficient of 525 mV /cm Oe.
Further enhancement in the magnitude of ME coefficient was obtained ͑595 mV /cm Oe͒ when the
angle of applied dc magnetic field was changed to 45°. Changing the intermediate piezoelectric
layer from single to trilayer stack geometry configuration leads to the realization of giant ME
response of 782 mV /cm Oe in sintered composites. © 2008 American Institute of Physics.
͓DOI: 10.1063/1.2966597͔
I. INTRODUCTION
Magnetoelectric ͑ME͒ particulate composites combine
the magnetostrictive and piezoelectric properties of
materials
1–3
through the product property of the system.
4
Compared to in situ composite synthesized by unidirectional
solidification of BaTiO
3
–CoFe
2
O
4
,
5–8
sintered particulate
composite is advantageous because of its cost effectiveness,
easy fabrication process, and better control of the process
parameters. On the other hand laminated ME composites
synthesized by using piezoelectric and magnetostrictive ma-
terials have gained attention because they exhibit superior
ME response. The laminates are generally fabricated by
sandwiching and bonding piezoelectric plate/disk/fibers be-
tween two layers of magnetostrictive plates/disks/foils.
9–15
Sintered particulate composites show inferior properties
compared to laminated composites because of the drawbacks
such as low resistivity, interface defects, interface diffusion,
mismatch in elastic compliance, and degradation in indi-
vidual material parameters. Previously, we have shown that
soft piezoelectric phase ͑high dielectric and piezoelectric
constant͒, soft magnetic phase ͑high permeability and low
coercivity͒, large piezoelectric grain size ͑Ͼ1
m͒, layered
structure, and postsintering thermal treatment ͑annealing and
aging͒ lead to the enhancement in magnitude of ME
coefficient.
16–21
In this study, we combine the advantages of
layered composite with that of sintering process and investi-
gate the geometrical and microstructural parameters that can
further enhance the performance of sintered ME composites.
II. EXPERIMENTAL
Previously, we have shown that pressure assisted sinter-
ing can provide trilayer composites with any desired dimen-
sions. Further, we have reported the compositions such that
sintering can be performed at low temperature of 900 °C,
which results in stable electrodes. In this study, we investi-
gate the effect of piezoelectric layer thickness in trilayer sin-
tered ME composite upon the ME coupling. Powders of
0.9Pb͑Zr
0.52
Ti
0.48
͒O
3
–0.1Pb͑Zn
1/3
Nb
2/3
͒O
3
͑PZT-PZN͒ and
Ni
0.6
Cu
0.2
Zn
0.2
Fe
2
O
4
͑NCZF͒ were synthesized using con-
ventional mixed oxide method and trilayers were synthesized
using the process described elsewhere.
22
In order to experimentally investigate the effect of thick-
ness ratio and achieve a higher ME coefficient, composites
of different piezoelectric thicknesses were synthesized.
NCZF composition was used as the magnetostrictive layer
and PZT-PZN composition was used as the piezoelectric
layer. The amount of NCZF was fixed at 0.7 g for top and
bottom layers, whereas the weight of PZT-PZN was varied
from 0.8 to 0.3 g. The interface electrode used in this study
was Dupont 6160 Ag–Pd conductor paste. The sintering was
done at 900 °C for 3 h using a load of 450 g, which is
equivalent to 50 kPa. After sintering each composite was
cross sectioned and polished for scanning electron micros-
copy. Figure 1͑a͒ shows the cross sections of trilayer com-
posite. The thickness of interface electrode observed in these
composites was in the range of 5–10
m. The adherence of
interface electrode with PZT-PZN and NCZF was found to
be good. The PZT-PZN grain size observed in all the com-
posites was above 1
m. X-ray elemental analysis was per-
formed using the scanning electron microscope in order to
identify any elemental diffusion through the electroded inter-
face. Figures 1͑b͒–1͑d͒ show the elemental analysis of Pb,
Fe, and Ag. A strong concentration of Pb was found on the
PZT-PZN side and Fe on the NCZF side. Ag was found to be
concentrated in the center region. By adding this interface
electrode the piezoelectric property was improved from 80
pC/N for cofired bilayer to 225 pC/N for trilayer composite.
ME coefficient ͑dE /dH͒ was determined by applying an
ac magnetic field at 1 kHz and 1 Oe amplitude ͑H͒ under
varying dc magnetic bias. The ac magnetic field was gener-
ated by a Helmholtz coil powered by Agilent 3320 function
generator. The output voltage generated from the composite
was measured using a SRS DSP lock-in amplifier ͑model SR
a͒
Electronic mail: spriya@vt.edu.
JOURNAL OF APPLIED PHYSICS 104, 044103 ͑2008͒
0021-8979/2008/104͑4͒/044103/5/$23.00 © 2008 American Institute of Physics104, 044103-1