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FEAT
Pedro Martins and Senentxu Lanceros-Mndez *
1.
Theelecmaof athehasin amewav
Iof tperwhima
Drialibiltionpiezoelectric and magnetostrictive components
produces an ME response several orders of magnitude higher than
those in single-phase ME materials. [ 10 ]
The ME effect in such composites is a product tensor prop-erty
which results from the cross interaction between the pie-zoelectric
and magnetostrictive phases in the multiferroic ME composite,
whereas the sum and scaling properties denote the
cign
m
atc
t
e have been proposed
Since the fi eld of researchas a complex taxonomy anferent fi
elds, [ 3 ] the basic conlisted and defi ned in Table 1
This Feature Article will ical developments and a disin the ME
research fi eld dumainly focus on polymer-baof polymer-based ME
matelaminated composites (Figucomposites (Figure 1 c) will
Then, the obtained ME materials will be ordered bmain possible
applications ture Article will end with some concluding remarks and
a sum-
polymer-based ME tic fi eld.
Polymer-Based Magnetoelectric Materials
Polymer-based magnetoelectric (ME) materials are an interesting,
chaland innovative research fi eld, that will bridge the gap
between fundamresearch and applications in the near future. Here,
the current state ofart on the different materials, the used confi
gurations for the developmof sobt rsom obasrem
DOI:
Prof. S. Lanceros-MendezCentro/Departamento de FsicaUniversidade
do Minho4710-057, Braga, PortugalE-mail: lanceros@fi sica.uminho.pt
Dr. P. Martins, Prof. S. Lanceros-MendezINL-International Iberian
Nanotechnology Laboratory4715-330 Braga, Portugal
Adv. Fu 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
mary of the distribution of the maximum coeffi cient by
reference, type, and DC magne 10.1002/adfm.201202780
nct. Mater. 2013, 23, 33713385Introduction
magnetoelectric (ME) effect, defi ned as the variation of the
trical polarization of a material in the presence of an applied
gnetic fi eld or as the induced magnetization in the presence n
applied electric fi eld, [ 13 ] can be seen as the bridge between
electric and magnetic properties of matter. [ 4 ] The ME effect
drawn increasing interest due to its potential applications reas
such as information storage, spintronics, multiple-state mories,
sensors, actuators, transformers, gyrators, micro-e devices,
optical waves, diodes, among others. [ 48 ] n order to positively
match the technological requirements hese and other applications, a
strong ME effect at room tem-ature has been obtained from
multiferroic (MF) composites, ch is generally obtained by combining
piezoelectric and gnetostrictive components. [ 9 ]
ifferent from what happens with the single-phase ME mate-s so
far available at room temperature, the larger design fl ex-ity of
MF composites allows the introduction of multifunc-al properties in
which the coupling interaction between the
to the which a chanmecha
MEH=
or,
MEE=
Equorders in MF positesmagne
Baseroom tdevices
ensors and actuators, as well as the main values of the ME
couplinained for the different polymer-based systems are
summarized. Fue of the specifi c applications that are being
developed for those p
ed ME materials are addressed as well as the main advantages
andaining challenges in this research fi eld. . [ 13 ] h described
in this Feature Article d typically involves terms from dif-cepts
of the ME research fi eld are . provide an overview on the
histor-cussion on the main achievements ring the last decades, and
will then sed ME materials. Three main types rials, nanocomposites
( Figure 1 a), re 1 b), and polymer as a binder
be then discussed. coeffi cients for polymer-based ME y
composite type and some of the will be discussed. Finally, this
Fea-URE A
RTIC
LE
average or the enhancement of effects which are already present
in the con-stituent phases. [ 5 ] In this way, composites can be
used to generate an ME response from the combination of materials
which themselves do not allow the ME phenomenon. [ 4 ]
Once a magnetic fi eld is applied to the composite, strain in
the magnetostrictive phase is induced. This is transmitted to the
piezoelectric constituent, which unde-goes a change in electrical
polarization. In an analogous way, the reverse effect can occur:
when an electric fi eld is applied
omposite, strain is induced in the piezoelectric phase s
transmitted to the magnetostrictive phase, leading to e in the
magnetization. The above mentioned coupling ism can be written as:
[ 11 ]
magnetic
mechanical mechanical
electric (1a)
electric
echanical mechanical
magnetic (1b)
tion 1 shows the coupling of the electric and magnetic rough an
elastic interaction. Therefore, the ME response omposites is an
extrinsic effect, dependent on the com- microstructure and the
coupling interaction across the ostrictive and piezoelectric
interfaces. [ 12 ] d on this property and the large ME effect
obtained at mperature for some composites, some prototype ME
lenging ental the ent
g ther, lymer-
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FEATU
RE
ARTI
CLE 1.1. History
Fouremer
Indiscoelecttricaldiscodiscometrnon-the tcessfeffecDzyain thand
Sat thof M
M
=
wereof ne
Inratiotechnthe nical imprME s
Inagainpositshiftecomppositthe tmagn
Thbeenneticpiezonatedc) pa
Toplentto reby a large
1.2. NAppl
The singl
Julius-Maximilians-Universitt Wrzburg, Germany. He was Research
Scholar at Montana State University, Bozeman, USA (19961998) and
visiting scientist at the A. F. Ioffe Physico-Technical Institute
(1995), Pennsylvania State
ersity (2007) and University of Potsdam (2008). He sociate
Professor at the Physics Department of the ersity of Minho,
Portugal and since 2012 he is Associate archer at the INL
(International Iberian Nanotechnology ratory). His work is focused
on the development of
mer-based smart materials and their applications.
Pedro Martins graduated in
d
s considered insuffi cient for most of the proposed
prac-plications. [ 43 ] In addition, there is a wide variation of
the on temperatures (paraelectric to ferroelectric, paramag-
antiferromagnetic, antiferromagnetic to ferromagnetic) single-phase
ME materials and a limited number of ls that exhibits ME behavior
at room temperature. [ 44 ] In y, most of these MEs can be only
used at low tempera- 10 K), which severely hinders the design and
applica- devices. ite ME coeffi cients obtained in ceramic MF
composites hree orders of magnitude higher than in single phase ls,
[ 45 ] such composites may become fragile and are lim- deleterious
reactions at the interface regions, leading electrical resistivity
and high dielectric losses > 0.1, hin-in this way the
incorporation into devices. [ 11 ] Apart from rementioned
disadvantages, ceramic composites still her problems such as being
expensive, dense and brittle, can lead to failure during operation.
[ 46,47 ] In this way, -based ME materials are not attractive from
a techno-
point of view.
Adv. Funct. Mater. 2013, 23, 33713385nlinelibrary.com 2013
WILEY-VCH Verlag GmbH & Co
years (1888, 1894, 1905, and 1926) were pivotal in the gence of
the ME research fi eld ( Figure 2 ): 1888, Rntgen, before winning
the Nobel Prize due to the very of the X-rays, observed that a
dielectric moving in a
ric fi eld became magnetized. [32] The reverse effect, the elec-
polarization of a dielectric moving in a magnetic fi eld was vered
by Wilson in 1905. [33] Between the fi rst and second veries
indicted above, Pierre Curie, in 1894, based on sym-y
considerations enunciated the possibility of ME effect in moving
crystals. [4,34] In 1926, Debye introduced and coined erm
magnetoelectricity for the effect that was not suc-ully proved
experimentally at that time. [35] n 1959, the ME t was predicted to
occur in chromium oxide (Cr 2 O 3 ) by loshinskii, [36] prediction
that was experimentally confi rmed e following year by Astrov. [37]
In 1966, the group of Ascher chmidt at the Battelle Institute in
Geneva and Newnham
e Pennsylvania State University discovered a high number E
boracites [38] and phosphates. [39] E coupling coeffi cients, defi
ned as
P
H (2)
not as high as necessary for applications, but the number w ME
materials increased signifi cantly. 1973, scientifi c work on ME
materials reached a satu-n point since it was felt that
single-phase MEs were not ologically applicable due to the weak ME
coupling and eed of very low temperatures. Furthermore, the
theoret-
considerations gave no indication or hope of signifi cant
ovements. [ 40 ] As a result of this dead-end, the intensity of
cientifi c activity strongly declined for almost 20 years. the
1990s, interest in ME materials strongly increased due to the
relationship between the ME and MF com-es: the main object of
scientifi c investigations into the ME d from single phase ME
materials, to the search for MF ounds with higher ME coupling. [ 41
] In those novel com-
es, the ME response is due to elastic coupling between wo
constituent phases, one piezoelectric and the other etostrictive. [
5 ] ree main types of bulk magnetoelectric composites have
investigated both experimentally and theoretically: a) mag-
metals/alloys e.g., laminated Terfenol-D or Metglas and electric
ceramics such as lead zirconate titanate; b) lami- Terfenol-D and
Metglas and piezoelectric polymers; and
rticulate composites of ferrite and piezoelectric ceramics. [ 42
] day, ME research is a strong research area, showing still y of
mysteries, promises, and challenges. One of them is place the
ceramic in bimorphs or superlattice composites polymer or
polymer-based piezoelectric matrix to achieve r areas or non-planar
structures. [ 13 ]
on Polymeric ME Materials: Problems Regarding ication
Developments
magnitude of the ME coupling coeffi cient in most of the e phase
MF materials is in the range of 120 mV/(cm Oe)
Univis AsUnivReseLabopoly
basetions
which itical aptransitinetic tofor themateriathis watures (
tions of
Despbeing tmateriaited byto low dering the afohave otwhich
ceramiclogical Senentxu Lanceros-Mendez graduated in physics at the
University of the Basque Country, Spain (1991), obtaining his Ph.D.
(1996) at the Institute of Physics of the
Physics and Chemistry in 2006 and received the PhD degree in
Physics in 2012, from the University of Minho, Braga, Portugal.
Part of his thesis work was in collaboration with the Basque
Country University, Spain and Cambridge University, United Kingdom,
concerning the development of polymer-based magnetoelectric
materials. His work is focused on polymer-
magnetoelectric materials for technological applica-and
electroactive polymers.
-
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FEA
noprocomMEtemshepro
2.
Astricnapomadis
Figand
Table 1. ME basic concepts.
Con
Mu le
Fer b
Fer b
Fer ca
Pie d
Pie c fi
es
Elec nc
Ma ct
Pie
coe
d t
m
s
Pie
coe
all
en
ss
Ma
coe
Ma
coe
Advcept Defi nition
tiferroic Material that possesses two or all three ferroic
properties (ferroe
roelectric Material that possesses a spontaneous and stable
polarization that can
romagnetic Material that possesses a spontaneous and stable
magnetization that can
roelastic Material that possesses a spontaneous and stable
deformation that
zoelectricity Variation of the strain of a material as a linear
function of an applied electric fi el
of applied stress.
zomagnetism Variation of the strain of a material as a linear
function of an applied magneti
function of applied str
trostriction Variation of the strain of a material as a
quadratic fu
gnetostriction Variation of the strain of a material as a
quadratic fun
zoelectric
ffi cient
Relates the mechanical strains produced by an applied electric
fi eld and is calle
components d ij , where i indicates the direction of
polarization generated in the
applied fi eld), and j is the direction of the applied
zomagnetic
ffi cient
Relates the mechanical strains produced by an applied magnetic
fi eld and is c
where i indicates the direction of magnetization generated in
the material wh
fi eld), and j is the direction of the applied stre 2013
WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2.1. PrepME Mat
Regardinymer-bapolymerand pylene) (P
MF Psolution
granules are fi rst dissolvedformamide (DMF)) at 75 of magnetic
fi llers is admechanical stirring processolution is poured onto a
eliminate voids and dried
Concerning the fabricatwo different methods havthe method
presented by Mof magnetostrictive nanoobtained mixture is then
pthat nanoparticles are weto avoid loose aggregates. [
is added. Further, the obtmechanical stirrer with ultrof the
polymer. Flexible fi lmtion on a clean glass substrcrystallization
are perfor
A more recent approach to obtain highly fl exible and nbrittle
ME composites and to solve all the aforementioned blems is to use
polymer-based nanocomposites. [ 13 , 48 ] In parison with the
ceramic ME composites, polymer-based
materials can be easily fabricated by conventional low-perature
processing into a variety of forms, such as thin ets or molded
shapes, and can exhibit improved mechanical perties. [ 13 ]
Polymer-Based Magnetoelectric Materials
previously mentioned, three main types of magnetoelec-
polymer-based composites can be found in the literature:
nocomposites, polymer as a binder, and laminated com-sites. In
the following section, the main characteristics, terials,
achievements, and limitations of each type will be cussed.
ure 1 . Types of polymer-based ME materials: a) nanocomposites,
b) laminated composites, c) polymer as a binder composites.
gnetostrictive
ffi cientRelates the mechanical strains produced by an applied
magnetic fi eld and is called the coeffi cient.
where i indicates the direction of magnetization generated in
the material when the magnetic fi eld is zer
fi eld), and j is the direction of the applied stress (or the
induced strain
gnetoelectric
ffi cientRelates the polarization/voltage produced by an applied
magnetic fi eld and is called the coeffi cient.
where i indicates the direction of polarization/voltage
generated in the material when the electric fi eld is
electric fi eld), and j is the direction of the applied magnetic
fi eld (or the induced m
. Funct. Mater. 2013, 23, 33713385aration of Polymer-Based
is a tensor, with components ij , o (or the direction of the
magnetic
).
[ 27,28 ]
is a tensor, with components ij ,
zero (or the direction of the applied
agnetization).
[ 30,31 ] TURE A
RTIC
LE
References
ctricity, ferromagnetism and ferroelasticity). [ 14,15 ]
e hysteretically switched by an applied electric fi eld. [ 16,17
]
e hysteretically switched by an applied magnetic fi eld. [ 18,19
]
n be hysteretically switched by an applied stress. [ 20,21 ]
or a change in the material polarization as a linear function [
21,22 ]
eld or a change in the material magnetization as a linear
s.
[ 23,24 ]
tion of an applied electric fi eld. [ 25,26 ]
ion of an applied magnetic fi eld. [ 27,28 ]
he strain constant, or the d coeffi cient. d is a tensor,
with
aterial when the electric fi eld is zero (or the direction of
the
tress (or the induced strain).
[ 25,26 ]
ed the d m coeffi cient. d is a tensor, with components d ij
,
the magnetic fi eld is zero (or the direction of the applied
(or the induced strain).
[ 27 , 29 ] 3373wileyonlinelibrary.com
erials and Interface Effects
g the preparation of particulate pol-sed ME nanocomposites, two
distinct s have been used, polyurethane (PU) oly(vinylidene fl
uoride-trifl uoroeth-(VDF-TrFE)), a copolymer of PVDF. U fi lms are
usually obtained by the cast method. In such method, PU in a
solvent (typically N,N-dimethyl- C for 1 h. Then, the desired
amount
ded to the polymer solution and a s is performed. Finally, the
obtained
clean glass substrate and degassed to at 70 C. [ 49 ] tion of
P(VDF-TrFE based MF fi lms, e been reported in refs [ 42 , 50,51 ]
. In artins et al., [ 42 , 50 ] the desired amount
particles is added to DMF and the laced in an ultrasound bath to
ensure ll dispersed in the solution and also 23 ] Afterwards,
P(VDF-TrFE) powder ained mixture is placed in a Tefl on asound bath
for complete dissolution s are obtained by spreading the solu-
ate. Solvent evaporation and polymer med inside an oven at
controlled
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3374
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wileyon
FEATU
RE
ARTI
CLE
tempsamp
Alpartican uprepaketoncrystais esselectr(900
Thpolymin thbetweonly charain dethe Mratio
Inoped nanointerfites cadvanthe istate
both the matrix and the inclusion and leads to changes in the
displacement fi eld and
Figureerature and crystallization is achieved by cooling down
the
2 . Highlights in the investigation of the ME effect.
linelibrary.com 2013 WILEY-VCH Verlag GmbH & Co. KGaA,
Weinheim
les to room temperature. ternatively, as reported in ref [ 51 ]
, magnetostrictive nano-les are dispersed in the P(VDF-TrFE)
solution matrix in
ltrasound bath. The P(VDF-TrFE) solution is previously red by
dissolving P(VDF-TrFE) pallets into methyl-ethyl-e (MEK). After
vacuum and thermal treatments, the fi nal llized MF fi lms are
obtained. Since electrical polarization ential to obtain
piezoelectric responses, the MF fi lms are ically poled by
submitting the fi lms to high electric fi elds kV/cm as a maximum
strength). e synthesis of the magnetostrictive nanoparticles used
in er-based ME particulate nanocomposites is well discussed
e literature. [ 5257 ] On the other hand, the interface effects
en nanoparticles and the polymer matrix has received little
attention. In this kind of MF nanocomposite, the cteristics of the
interface becomes a prominent factor [ 58 ] termining the
magnetoelectroelastic properties as well as E effect of the MF
nanocomposite, due to the increasing
of the interfacial area to volume. recent years, surface
elasticity theory [ 59 ] has been devel-to account for the effects
of surfaces and interfaces at the meter-scale. These studies show
that depending upon the ace design, the effective properties of the
nanocompos-an be either enhanced or reduced. [ 60 ] In this way,
taking tage of the theory of linear elasticity, it was found
that
nterfacial stress displays short-range effect on the stress in
nanocomposites, which introduces internal stresses in
reduction of the piezoelecinterface is even more harposites. A
proper Terfenol-the perfect coupling betwestrains without
appreciableroughly decrease the displeading to a decrease in th
Continuing their study ME response of Terfenol-Nan et al. [ 63 ]
discussed thecomposite. This coupling formulation by using the
Ginterfaces between Terfendecrease the displacementa decrease in
the ME respwhen the particle sizes weof the imperfect interface
large amount of interfacestechnologically important pnetostrictive
composites ththe quantitative correlatifor composites and their
iexplored.
Theoretical calculationsMF particulate composite (PZT), and
polymer has Greens function techniquthe ME voltage coeffi ciene
surfactant modifi cation leads to a tric response. Thus, such an
inactive mful to the ME response of the com-D particles/polymer
interface ensures en these phases, transferring elastic losses. Any
imperfect interfaces will lacement transfer capability, thereby e
ME response of the composites. on the effects of the interface on
the D/P(VDF-TrFE) layered composites, effective coupling properties
of such was expressed in a convenient matrix reens function
technique. Imperfect
ol-D and P(VDF-TrFE) phases would transfer capability, thereby
leading to onse of the composites. In particular, re at the
nanometer scale, the effect would be more pronounced due to a in
the composites. However, in the iezoelectric ceramic/epoxy and
mag-
at have been extensively investigated, on between the coupling
behavior nterface imperfection remains to be
of the ME properties in a three-phase of Terfenol-D,
lead-zirconate-titanate been also reported [ 64 ] based on the e.
It was shown that the values of ts are very sensitive to
mechanical
Adv. Funct. Mater. 2013, 23, 33713385the stress fi eld created
by a external loading. Shrinkage of the inclusion was also
observed. Unlike the classical results, in the theory of linear
elasticity, the effective bulk modulus is a function of the
interfacial stress and the size of the inclusion. [ 61 ]
The nonclassical interface condition has also been studied by
Pan et al. [ 60 ] and it was observed that such interface condition
exerts a signifi cant infl uence on the local and overall
magnetoelectroelastic responses of MF com-posites, in particular
when the fi llers are at the nanometer-scale. It was also
demonstrated that it was possible to enhance the ME coeffi -cient
of a MF composite consisting of magne-tostrictive fi llers
reinforced in a piezoelectric matrix by designing an electrically
highly con-ducting interface.
Keeping the interface of nanocomposites as subject of study, but
in an more experi-mental approach, Nan et al. [ 62 ] have
inves-tigated the role of the Terfenol-D/polymer interface layer,
induced by surfactant modifi -cation of the Terfenol-D particle
surfaces, in the ME properties of the composites. It was reported
that by adding a silane surfactant to the surface of the
nanoparticles, the piezo-electricity of the composite is diminished
since th
-
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K
FEAmagnetostrictive components of a MF layered composite. The
ezM c)a re nenr srgd
bh th
aeliiiahfs
av ddy
ftr/lb
eiit
mns
8
co
boundary conditions of the composite sample, and that the
polarfacialon thof thME rarticlganiceffectpositwas
opositlargelargeinterfThe than dynacomp
Reeffectpositobserexhaubeenelectrroele
Anrite cas ththe ato thsurfaThis mer-bmentdevicthosethe ean
eptop o
Inthat idepenconstSuchbetwefor an
BaelemstudinetosdepenBasedthe ithin,
Inet al.of th
Adv. Fu 2013 WILEY-VCH Verlag GmbH & Co.
increasthe piein the are MEthe thi( < 0.001It was epoxy fiby
decusing abetweebecomweak itransfenent toin the in a laexpecteepoxy
bility, tlayered
Anomentedeffect ccase, thspin-podielectrdielectrto applthan
th
In tmost ocomposimilarinorganeffect clinear electriceffects
reporterecentlobservafaces o
Conthe Nia novemined the intoscillatmore, to the dtype of
ChaFe, denet al., [ 8
BaTiO 3interfaanisotr
ization orientation in PZT particles and the inactive inter-
layer surrounding PZT particles have a signifi cant effect e ME
response of the composite. The quantitative analysis e effect of
such mechanical boundary conditions in the esponse of the
composites will be later discussed in this e. Interface effects
have been already addressed in inor- ME composites. In particular,
additional to the interface s in the ME response of BaTiO 3 /NiFe
1.98 O 4 nanocom-
es, Sreenivasulu et al. [ 65 ] also reported the size effects.
It bserved that the particulate BaTiO 3 /NiFe 1.98 O 4 nanocom-
es exhibit large ME coeffi cient values (about fi ve times r)
than the BaTiO 3 /NiFe 1.98 O 4 microcomposites due to the
piezoelastic dynamic strain coeffi cients and an adequate ace
contact between both BaTiO 3 and NiFe 1.98 O 4 phases.
magnetostriction was higher in nanograined NiFe 1.98 O 4
micrograined NiFe 1.98 O 4 and thus, the magnetostrictive
mic coeffi cient was proposed to have large values for
nano-osites than the microcomposites of similar compositions.
garding the experimental study of the interface and size s on the
ME properties of polymer-based ME nanocom-
es and polymer as a binder composites it is therefore ved a
clear need of further investigation. A systematic and stive study
of the effect of the PVDF/ferrite interface has
nevertheless reported concerning the nucleation of the oactive
-phase of PVDF, and consequently in their fer-ctric, piezoelectric
and ME properties. [ 6670 ] interesting outcome of this
investigation on PVDF/fer-omposites is the fact that the ferrite
nanoparticles used e magnetostrictive phase in the ME
nanocomposites have bility to nucleate the electroactive -phase of
PVDF, [ 66 ] due e electrical interactions between the negative
nanoparticle ces and the positively charged polymeric CH 2 groups [
69 , 71 ] . fact will allow to reduce the production costs of the
poly-ased ME nanocomposites, [ 72 ] leading to the develop- of
applications of such as didactics, toys and disposable es. [ 13 ]
Focusing on layered or laminate ME structures, confi gurations are
usually obtained by gluing together lectroactive polymer and the
magnetostrictive phase using oxy binder [ 9 , 7376 ] by the direct
deposition of one phase on f the other, [ 77,78 ] or by hot-molding
techniques. [ 79,80 ] such ME layered composites, the quality of
the interface s determined by the interface coupling parameter is
only dent on surface inhomogeneities and interactions between
ituents during the preparation as well as misfi t strains. a
parameter is a measure of differential deformation en the
piezoelectric and magnetostrictive layers and k = 1 ideal interface
and k = 0 for the case without coupling. [ 5 ]
sed on modifi ed constitutive equations and the fi nite ent
method, the quality of the MF interface has been ed. [ 81 ] It was
verifi ed that the ME effect of laminated
mag-trictive/piezoelectric MF nanocomposites was remarkably dent on
the thickness and characteristics of binder layer. on the
constitutive equations, results show that, when
nterfacial layer is somewhat stiff and the binder layer is a
large ME effect will be produced. order to treat such an
interfacial bonding effect, Nan [ 82 ] changed the shear modulus
and the relative thickness e conductive epoxy used for bonding the
piezoelectric and
nct. Mater. 2013, 23, 33713385 3375wileyonlinelibrary.comGaA,
Weinheim
TURE A
RTIC
LE
in the thickness of the conductive epoxy fi lms between
oelectric and magnetostrictive phase leads to a decrease E voltage
coeffi cients, since the conductive epoxy fi lms
inert. It was also reported that a very low ratio between kness
of epoxy and thickness of the MF composite is good enough for
producing a giant ME response. lso discovered that the elastic
modulus of the ME inert lms has a signifi cant effect on the ME
response values, asing the shear modulus of the thin epoxy fi lms,
i.e.,
very fl exible epoxy as the binder, the interfacial bonding the
piezoeletric and magnetostrictive components s weak due to the
formation of a sliding interface. The terfacial contact would lead
to appreciable losses of ring elastic strain/stress from the
piezoelectric compo-the magnetostrictive component, and thus the
decrease hear modulus of the thin interfacial epoxy fi lms results
e decrease in the ME response of the composites. As , any imperfect
interfacial bonding produced by the
inders would decrease the displacement transfer capa-ereby
leading to a decrease in the ME response of the composites. er type
of interface ME coupling has been imple-
by Rondinelli et al. [ 83 ] It was demonstrated that the ME n
arise from a carrier-mediated mechanism. In such magnetic response
is mediated by the accumulation of arized carriers at the interface
between a nonmagnetic c and a ferromagnetic metal. For the
ferromagnetic/c interface, this kind of ME effect is linear with
respect ed electric fi eld and the magnitude is two orders lower t
for the interface bonding mechanism. e case of
ferromagnetic/ferroelectric heterointerfaces, the studies have been
reported in all the inorganic ME ites, though it is expected that
the main behaviors are for polymer-based ME materials. For example,
in the ic ME composite SrRuO 3 /BaTiO 3 interface, [ 84 ] the ME n
be further enhanced owing to fi eld effect and non-ariation of the
ferroelectric polarization with applied fi eld. Experimental
manifestation of the predicted ME riven by these purely electronic
mechanisms were later for the La 0.8 Sr 0.2 MnO 3 /PbZr 0.2 Ti 0.8
O 3 bilayers. [ 85 ] More
, the interface bonding ME effect was verifi ed by the tion of
room-temperature multiferroicity at the inter- BaTiO 3 ultrathin fi
lm with Fe or Co. [ 86,87 ] ary to the case of Fe/BaTiO 3 system
mentioned above,
BaTiO 3 structure reported by Dai et al., [ 87 ] has shown type
of interface bonding ME effect, which is deter-y the change of
magnetic moments on Ni atoms near
rface, and that there existed an extraordinary intralayer on of
magnetic moments within the Ni layer. Further- was demonstrated
that the underlying physics was due ifferent interfacial electronic
structure and the different
agnetic interaction. [ 87 ] ging the Ni component reported by
Dai et al. to the ity-functional calculations were employed by
Lukashev
] to investigate the effect of ferroelectric polarization of on
the magnetocrystalline anisotropy of the Fe/BaTiO 3 e. It was found
that the interface magnetocrystalline py energy decreased (from
1.33 to 1.02 erg cm 2 ) when
-
3376
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wileyonlin
FEATU
RE
ARTI
CLE an optimal value of H DC and therefore a peak in the value
vs H DC plot, [ 42 , 93 ] experiments show that remains more or
the ferroelectric polarization was reversed. This strong ME coup
ling was explained in terms of the changing population of the Fe
3tion rev
It haas PVDto the fas inteusing PVDF electricline anwas
shomagneby 50inducedwith Cface ma
In thME effa viableheterosthe intstructu
The of PVDence. [ 77
pared busing camounPVDF stress. tive macould amagnemechan
2.2. Par
When smallerites havas pieznanocopropert
In thesting the truethe coethe fi lleorder o18
mVcouplinmagne
The PU/Nictively apredictelibrary.com 2013 WILEY-VCH Verlag GmbH
& Co
less contion strthe matME comas the MmagnetFe 3 O 4 oits
origithe lineand thepolymeites is mmatrix cfor the
additioncomposthe bonpreventnanocomsuch na
RegaME nangiant Mtric polyreports CoFe 2 Omatrix osince thages
beroelectrof PVDferrite nnetic anthe caseMF fi lmpolarizavalue
oTrFE)/Napplied obtaine
In coCoFe 2 Oof the fmagnetvalue vsbetweenTrFE)/Cence in
Zhanthe moP(VDF-roelectrconcentmental kind ofcients ofi rmed
d orbitals at the Fe/BaTiO3 interface driven by polariza-ersal.
s been also reported, [ 89 ] that organic ferroelectrics, such F,
have an additional advantage of being weakly bonded erromagnet,
thus minimizing undesirable effects such
rface chemical modifi cation and/or strain coupling. By fi
rst-principles density functional calculations of
Co/heterostructures it was demonstrated the effect of ferro-
polarization of PVDF on the interface magnetocrystal-isotropy that
controls the magnetization orientation. It wn that switching of the
polarization direction alters the
tocrystalline anisotropy energy of the adjacent Co layer %,
driven by the modifi cation of the screening charge by
ferroelectric polarization. The effect was reduced
o oxidation at the interface due to quenching the
inter-gnetization. is way, ref. [ 89 ] indicates that the
electronically assisted
ects at the ferromagnetic/ferroelectric interfaces may be
alternative to the strain mediated coupling in related tructures
and the electric fi eld-induced effects on erface magnetic
anisotropy in ferromagnet/dielectric res. infl uence of interfacial
effects on the ME properties F based ME composites was also studied
in the refer- ] Flexible SmFe/PVDF laminate composites were pre-y
depositing of SmFe nanoclusters onto the PVDF fi lm luster beam
deposition method. Since there was a small t of residual argon
carrier gas molecules in the SmFe/fi lm, it was actually subjected
to a residual compressive Accordingly, under the combination infl
uence of nega-gnetostriction and compressive stress, the SmFe fi lm
lso generate the magnetic anisotropy with an in-plane
tic easy axis, which allows a more effi cient
magnetic-ical-electric coupling along the interface.
ticulate Nanocomposites
compared to their ceramic ME counterparts, a much variety of 03
type ME polymer-based nanocompos-e been reported in the last two
decades. Polymers such oelectric PVDF and PU have been used in such
ME mposites due to their good piezoelectric/electrostrictive ies. [
90,91 ] e electrostrictive PU-based ME composites several
inter-results have been obtained, including the extraction of ME
current from the total output current response and xistence of both
linear and quadratic ME responses in d PU fi lm. The obtained
linear ME effect is of the same f magnitude as that of the Cr 2 O 3
single crystal (up to
cm 1 Oe 1 ) and a possible linear magnetoelastoelectric g
between fi llers and polymer matrix not triggered by
tostriction has been also proposed. [ 92 ] linear voltage ME
coeffi cients obtained in PU/Fe 3 O 4 and kel composites were 11.4
and 6.0 mV cm 1 Oe 1 , respec-t 7 Hz, 0 DC fi eld and 1 Oe AC fi
eld. Even when it is ed that due to the magnetostriction it should
be found . KGaA, Weinheim
stant with increasing H DC . This experimental observa-ongly
suggested that the magnetostrictive properties of erial have no
infl uence in the PU/Fe 3 O 4 and PU/Nickel
posites. This interesting fact has been confi rmed E response in
PU composites is independent of the
ostrictive properties of the fi llers such as Terfenol-D, r
Nickel. [ 49 ] In this way, the ME coupling does not have n in the
magnetostriction of the particles but rather in ar elastic
interaction between those particle aggregates highly polar
microdomains of the semi-crystalline
r PU. [ 9395 ] Consequently, the coupling in PU compos-ainly due
to the particular nature of the elastomer PU
omposed of both rubbery and polar domains. A support
aforementioned mechanism is the fact that the simple of morphous
carbon nanopowder into PU based ME ites enhances the quasistatic
strain amplitude [ 96 ] since ding between the PU polymer and
carbon nanopowder s slippage and effectively improves the strain in
the
posite. [ 97 ] In any case, the origin of the ME coupling in
nocomposites is not yet clearly established. [ 6 ] rding the use
PVDF as the piezoelectric constituent of ocomposites and after the
theoretical calculations of
E on ferromagnetic rare-earth-iron-alloys-fi lled ferroelec-mers
in 2001 by Nan et al., [ 63 , 98 ] two main experimental can be
found in the literature. Martins et al. introduced 4 and Ni 0.5 Zn
0.5 Fe 2 O 4 ferrite nanoparticles into a polymer f (P(VDF-TrFE).
P(VDF-TrFE) was used instead of PVDF e copolymers of PVDF,
containing VDF molar percent-tween 55 and 82, crystallizes from the
melt in the fer-ic phase which is an essential factor for the
preparation F based ME nanocomposites. [ 99100 ] The
P(VDF-TrFE)/anocomposites exhibit ferroelectric, piezoelectric,
mag-d direct ME effect dependent on the ferrite loading. In of
P(VDF-TrFE)/CoFe 2 O 4 nanocomposite, the resultant s showed
saturated hard magnetic properties, improved tion and piezoelectric
response and a maximum 33 f 41.3 mV cm 1 Oe 1 . On the other hand,
for P(VDF-i 0.5 Zn 0.5 Fe 2 O 4 composites, 33 increases linearly
with H DC and a 1.35 mV cm 1 Oe 1 maximum value was
d for samples with 15 wt% ferrite. [ 50 ] ntrast to PU based
composites, [ 49 ] the ME P(VDF-TrFE)/ 4 response is strongly infl
uenced by the magnetostriction errite nanoparticles since an
optimal value of the H DC ic fi eld was observed and consequently a
peak on the H DC plot appears ( Figure 3 ). The observed difference
the in plane and out-of-plane ME response of P(VDF-oFe 2 O 4
nanocomposites was fully attributed to the differ-the d 33 and d 31
P(VDF-TrFE) piezoelectric constants. [ 101 ] g et al. studied the
effect of CoFe 2 O 4 nanoparticles on rphology, ferroelectric,
magnetic and ME behaviors of TrFE)/CoFe 2 O 4 nanocomposites. Once
again, the fer-ic and ME responses are strongly infl uenced by the
ration of ferrite nanoparticles. [ 51 ] A signifi cant experi- 33
value around 40 mV cm 1 Oe 1 was obtained in this nanocomposites.
Both experimental ME voltage coeffi -f Martins et al. and Zhang et
al. were theoretical con-by a relatively simple model based on
those of Wong
Adv. Funct. Mater. 2013, 23, 33713385
-
www.afm-journal.dewww.MaterialsViews.com
FEA
oice-Drdrf icla0ppld
spatnit
dl- co
10
celd
and Srespon
33 =
where
L E =
dHpdH
=
Here, respectric cophaserespeczationnanoc
Posalso ssized by Hemagneites wbut threport
2.3. Po
UnlikepositeME metrostr
Figure 3from re
. c.
Adv. Funstress cnetostr
Threand PV
In o f , of Temixturedielectra percothan 0.ME resME
resthreshoonly refor 33 less thacomposmainlyTerfenothe MEto
imprcles [ 106,
ferrite thresho
hin [ 102 ] and Zhou and Shin. [ 103 ] In this model, the ME se
33 can be expressed as:
(1 ) L E
(d31p
dYxpdHm
+ d32p dTypdHm
+ d33p dTzpdHM
)(dHmdH
)
(3)
L E and dHpdH
are given by:
[m + 2p ]
][(1 ) m + (2+ ) p
]
(4)
3p
(1 )(m + dMmdHm
)+ (2+ ) p
(5)
p and m indicate the polymer and magnetic phase tively; d 3n the
piezoelectric coeffi cients; the dielec-nstant, the volume fraction
of the magnetostrictive
; T and H are the stress and applied magnetic fi eld, tively;
the magnetic permeability and M the magneti-. dMm is obtained from
the magnetization curve of the
. Comparison between the responses of P(VDF-TrFE)/CoFe 2 O 4
(data f. [ 42 ] ) and PU/Fe 3 O 4 ME nanocomposites (data from ref.
[ 49 ] ).
Figure 4polymerref. [ 64 ] ) 2013 WILEY-VCH Verlag GmbH &
Co. KG
i) the min the
ii) a soft D nan
Althouallows hthe seconresponseFeature Athis MF
taneouslyoptimizafact, theoboundarythe Greeical boun
dHmomposites. sible ME polymer-based nanocomposite structures
were ynthesized using conducting polyaniline and nano-BiFeO 3
particles through in situ solgel polymerization malatha et al. [
104 ] The morphology, crystalline structure, tic, and optical
properties of polyaniline/BiFeO 3 compos-
ith various concentrations of nanofi ller were discussed e ME
response of such nanocomposites has not yet been ed.
lymer as a Binder Composites
in the previous section, in the poly mer as a binder com-s the
polymer is not used as the piezoelectric phase of the aterial but
as a binder for the piezoelectric and magn-ictive particles that
keep them together and provides the
ct. Mater. 2013, 23, 33713385TURE A
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LE
upling between the piezoelectric matrix and the mag-tive fi
llers. phase particulate composites of Tefenol-D alloy, PZT F [ 72
] ( Figure 4 ) were the fi rst to be studied. er obtain the ME
response, a small volume fraction, enol-D nanoparticles were
dispersed in a PZT/PVDF by a simple blending technique and the
obtained , piezoelectric and ME properties demonstrate that tion
transition occurs at f 0.12. When f is lower
7 the MF composites exhibit good piezoelectric and onses but
when 0.07 f 0.12 the piezoelectric and onse sharply drops and
disappears at the percolation , above which the composite becomes a
conductor and ond magnetostrictively. The maximum obtained value
2KOe was about 42 mV cm 1 Oe 1 at f = 0.06 which is half with those
obtained for the PZT/ferrite ceramic e (115 mV cm 1 Oe 1 ). [ 105 ]
Since this ME response is etermined by the f Terfenol-D , the
pre-treatment of the D nanoparticles, by the use of surfactants can
change oupling.. Surfactants are usually used in such a way ve
dispersibility and dispersion stability of nanoparti-7 ] in
different kind of matrices. In the case of the PZT/ramic composite,
surfactants increase the percolation . This experimental change has
two consequences:
aximum magnetostrictive fi ller concentration allowed ME
nanocomposites is increased;
and inactive interfacial layer is induced in the
Terfenol-oparticles.
Schematic representation of the particulate
Terfenol-D/PZT/omposites (based on an experimental description
reported in 3377wileyonlinelibrary.comaA, Weinheim
gh the fi rst consequence is extremely positive since it igher
magnetostrictive content in the ME composite, d produces a negative
effect on both the piezo and ME of the nanocomposites as already
discussed in this rticle. [ 62 ] Further improvement in the ME
response of
composite lies in increasing the f Terfenol-D and simul-
ensuring good interfacial contact between phases by
tion the nanocomposite processing. In view of this retical
calculations were performed on the mechanical conditions infl uence
in the ME properties based on
ns function technique. [ 98 , 108 ] Three different mechan-dary
conditions were considered:
-
3378
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wileyonl
FEATU
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CLE i) completely mechanical clamped boundary condition; ii)
com
iii) comin
Forare 11respecparticlhave
apositeparticlcompoeffect.constaeffectieffect the PZ
Thesame Polymrate-dopoly(mTerfencance the saOe 1 , matrixtivity
e
Altheasy sattractfeaturparticu
2.4. La
In thpositenanocrespona diffecompo
A lapositeparticuleakagpiezoeand it tions t
MFPVDFPZT/Phas bea bindnated low coites as
to low ME performance. The ME properties are improved in the
inelibrary.com 2013 WILEY-VCH Verlag GmbH & Co
pletely mechanical free boundary condition; pletely mechanical
clamped in the zz direction and free
the transverse direction.
the composite with f = 0.06, the maximum 33 values 7, 362, and
62 mV cm 1 Oe 1 for situations i), ii) and iii), tively. The same
calculations also revealed that the PZT es polarization and the
inactive PZT/PVDF interface signifi cant effect on the ME
properties of the nanocom-s. Random orientations of the
polarization in the PZT es result in the disappearance of
piezoelectricity in the sites, and thereby the disappearance of the
extrinsic ME
Although the thin interfacial layer with the same elastic nts as
the polymer matrix has only a slight effect on the ve
magnetostriction of the composites, the piezoelectric is strongly
infl uenced by the interfacial layer surrounding T particles. [ 64
] infl uence of different polymers in the ME response of the kind
of MF nanocomposites was recently investigated. [ 109 ] er
electrolyte polyethylene (PEO) and lithium perchlo-ped PEO, lithium
perchlorate-doped PEO (Li + -PEO) and ethyl methacrylate) (PMMA)
were mixed separately with ol-D and PZT particles aiming to
evaluate the signifi -of the polymer matrix conductivity in the ME
response of mples. The obtained 31 were 1.3, 3.2, and 4.8 mV cm 1
respectively, for the Li + -PEO, PEO and PMMA polymer . Those
results confi rm that samples with higher conduc-xhibit lower ME
responses. [ 72 ] ough the fl exibility, structure, simple
fabrication, and
haping of the polymer as a binder ME materials provide ive
advantages in possible ME applications, these added es are limited
since all of them are inferior to those of the late
nanocomposites.
minated Composites
e three-phase Terfenol-D/PZT/PVDF particulate com-s of the
previous section, the f Terfenol-D allowed in the omposites is
quite low, which strongly limits the ME se of the MF nacomposites.
To eliminate this limitation, rent class of ME material has been
developed: laminated sites. minate bilayer or multilayer confi
guration for ME com-
s has other advantages over bulk nanocomposites. In lar, the
loss of polarization in bulk composites due to
e currents can be overcome in layered structures. The lectric
phase can be poled to enhance the ME coupling is also possible to
vary the poling and applied fi eld direc-o achieve maximum ME
coupling. laminated composites consisting on one Terfenol-D/
particulate composite layer sandwiched between two VDF particulate
layers prepared by hot-molding technique en reported. [ 80 ] The
polymer phase PVDF is used just as er, with no infl uence on the ME
properties of the lami-composite. Experiments show that with f PVDF
0.3, the ncentration of PVDF leads to low quality of the compos-
the connection between the three phases is poor, leading
intermas f PVDinert PME actcompoobtainesensiviOe 1
atferencesitivity,the aninetostrin out-the PZ
Novsistingtwo Teinvestigsitivity below quencyites is thicknethe
PZ( L ) equby incr( t p ) Thea 2/7 reffectiv t p / L , this due the
lam
FinafabricaInc., Utigatedthe equ0.5 in tPZT coepoxy l504 OeOe 1
, rWhen incre0.6 andThe inincreasthat thdecreas
A simcouplintive mabi and one or modelehighesFe 3 O 4 /Oe 1 at.
KGaA, Weinheim
ediate f PVDF concentration range (0.3 f PVDF 0.5) and F further
increases ( f PVDF > 0.5), the high concentration of VDF causes
weak dielectric, magnetostrictive, piezo and ivity of the
three-phase laminated Terfenol-D/PZT/PVDF sites. A maximum value
for 33 of 80 mV cm 1 Oe 1 was d at 1 kHz, 4 kOe, and f PVDF = 0.5.
The maximum ME ty of such laminated composites can reach up to 3 V
cm 1 a resonance frequency of around 100 kHz. [ 110 ] The dif- in
the longitudinal ( 33 ) and transversal ( 31 ) ME sen- 3 and 3.8 V
cm 1 Oe 1 , respectively, is fully attributed to sotropy of the
laminated ME samples. At high bias, mag-iction becomes saturated
faster under in-plane bias than of-plane bias producing a nearly
constant electric fi eld in T, thereby decreasing 31 with
increasing bias. el laminated conformations of the ME samples, con-
on a PZT/PVDF particulate layer sandwiched between rfenol-D/PVDF
particulate composite layers [ 111 ] were ated. With this
conformation, the maximum ME sen- 33 was improved to 300 mV cm 1 Oe
1 at a frequency
50 kHz and about 6 V cm 1 Oe 1 at the resonance fre- of around
80 kHz. The ME response of such compos-also strongly dependent on
the applied bias and on the ss ratio ( t p / L ) between the
Terfenol-D/PVDF layers and T/PVDF layer. Keeping the thickness of
the composite al to 2.5 mm, the t p / L ratio was varied from 1/7
to 5/7 easing the thickness of the PZT/PVDF particulate layer
values of the composites fi rst increase with t p / L until atio,
which could be attributed to the increase in the e piezoelectric
effect. However, with further increasing e ME sensitivity declines
after a maximum value, which to the reduction in magnetostrictively
induced strain of inated composites with increasing t p / L . [ 79
] lly, three-phase Terfenol-D/PZT/binder composites were ted by
substituting PVDF by Spurr epoxy (Polysciences SA). [ 112 ] The ME
properties of such materials were inves- experimentally and
theoretically confi rmed by the use of ivalent circuit approach. [
113 ] Samples with a f Terfenol-D = he Terfenol-D/Spurr epoxy
laminates with two different ncentrations ( f PZT = 0.6 and f PZT =
0.75) in the PZT/Spurr aminate were measured. At a frequency of 10
kHz and fi eld, the obtained value for 31 was 0.3 and 0.4 V cm 1
espectively for the f PZT = 0.6 and f PZT = 0.75 samples. the
frequency was changed to the resonance ( 55 kHz), ases up to 10 V
cm 1 Oe 1 in the case of the f PZT = 11 V cm 1 Oe 1 in the case of
the f PZT = 0.75 composite. crease of with increasing f PZT is
expected, due to the e of the piezoelectric phase. It is
nevertheless to notice e improvement of the ME response is
accompanied by a e of the fl exibility and strength of the
composite. ilar ME composite concept uses PU to increase the ME
g between the piezoelectric PVDF and the magnetostric-terial (Fe
3 O 4 and Terfenol-D). [ 114 ] It was reported a ME in trilayered
composites consisting in on layer PVDF and two layers of PE fi lled
with Fe 3 O 4 or Terfenol-D particles, d by a driven damped
oscillation system, [ 115,116 ] with a
t 33 obtained for the trilayered sample of PE + 2 wt% PVDF/PE +
2 wt% Fe 3 O 4 with a value of 753 mV cm 1 2000 Oe.
Adv. Funct. Mater. 2013, 23, 33713385
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www.afm-journal.dewww.MaterialsViews.com
FEAa PVDF/Metglas 2605SA1 laminate a composite at a non
reso-nance frequency of 20 Hz and at 3 Oe DC magnetic fi eld. [ 74
] k0i D
e
ti
e cfc
1
tof
6
d. [
acc bmeot
ot or
ao
te
. vsT
FurtTerfenoand a Pepoxy, [ 1
f Terfenol-due to fi cient 2.7 V cin the m
A bilD/low vonance0.924 Vrespectto the sandwiME restime re
Thinfabricatmagnemorphconfi gu
Thosin orderequirenetic fi and excmagnetogethehave a 238 V cboth
nelower fobtaineMetglagiant meffectivto four10 6 Olow H DPVDF
potenti
AftepositesME mafl ux coaspect
Figure 5b) unim(c) are b
Adv. Func By taMP401composweak H
i) larghigh
ii) highMP4
iii) relaMP4
Sincvoltageization PVDF PVDF/MOe 1 at
Furthprone types oties of Pnates. [ 7
ally usepoling300 MVtemperlow eleuntil a utilizedparing vs DC
attributmagnetrelated tion ofof the mzomagnimum the faccyclic
pferent o 31 obtvalues laminaof the mtions inpoling)
A noites waP(VDF-
her, ME laminates of vinyl ester resin (VER)-bonded l-D
magnetostrictive layer ( f Terfenol-D from 0.16 to 0.48) ZT
piezoelectric layer glued together with a conductive
17 ] show 31 values increasing gradually with increasing
D in the MS layer reaching a saturation for f Terfenol-D >
0.4 the increasing elastic modulus and piezomagnetic coef-of the
magnetostrictive phase. A maximum value of m 1 Oe 1 was obtained at
666 Oe DC fi eld with f Terfenol-D
agnetostrictive layer equal to 0.48. ayer disk prepared by
bonding a PZT disk with Terfenol-iscosity epoxy disk [ 118 ] show
at a bias of 3 kOe three res-
peaks with 33 values of 2.79 V cm 1 Oe 1 at 35 kHz, cm 1 Oe 1 at
100 kHz and 1.31 V cm 1 Oe 1 at 122 kHz ively. [ 119 ] The
resonance peak at 122 kHz is attributed transversal resonance, [
120,121 ] which is present in many ch laminated composites. [ 80 ,
122 ] The observation of three onance peaks in laminated composites
is for the fi rst ported in this work. , fl exible ME laminates (
Figure 5 a) composites were ed following similar approaches but
with different
tostrictive layers, as for example, Metglas/PVDF uni- (Figure 5
b) and threelayer (Figure 5 c) sandwich rations. [ 73 ] e laminates
required an applied H DC of only 8 Oe r to achieve a maximum ME
response, 1/50th of that d for the previous ME laminates. These
small mag-eld ME laminates have giant ME voltage coeffi cients
ellent sensitivity to small variations in both AC and DC
tic fi elds. The Metglas layer and PVDF layers are glued r using
an epoxy and both laminate types were found to strong ME
enhancement: three-layer composites: 31 = m 1 Oe 1 ; unimorph
composites: 31 = 310 V cm 1 Oe 1 , ar the longitudinal resonance
frequency at 50 kHz. At
requencies, a maximum value of 7.2 V cm 1 Oe 1 was d for both
geometries. Although the magnetostriction of s SA1 was only 42 ppm
which is far smaller than the agnetostriction of Terfenol-D, the
maximum value of its
e piezomagnetic coeffi cient d 33m = 4 10 6 Oe 1 is three times
larger than the one for Terfenol-D d 33m = 1.2 e 1 due to the small
saturation fi eld. [ 123 ] This extremely
C requirement is an important advantage of Metglas/
. a) Picture of a fl exible PVDF/Metglas unimorph laminate; orph
confi guration, and c) three layer laminate. (Panels (b) and ased
on the experimental description reported in ref. [ 73 ] ). 2013
WILEY-VCH Verlag GmbH & Co. K
ance imlinking amatrix wand conto those electric P(VDF-T
laminates over other previously reported types, offering al in
practical applications. r the fi rst works on Metglas/PVDF laminate
nanocom-, [ 73 ] several works were devoted to these promising
terial. For example, taking advantage of the magnetic
ncentration effect of Metglas as a function of its sheet ratio
values of 31 = 21.46 V cm 1 Oe 1 were obtained in
t. Mater. 2013, 23, 33713385 3379wileyonlinelibrary.comGaA,
Weinheim
TURE A
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LE
ing advantage of the anisotropy of PVDF/Metglas-SA1-XGDC
laminates it was demonstrated the ability of such tes to be used as
an ultra-sensitivity detection device of
C (1 10 9 Oe). [ 9 ] This high sensitivity is due to the:
piezoelectric voltage coeffi cient of PVDF that indicates a
output voltage in response to a small variation of strain;
piezomagnetic coeffi cient of the Metglas-SA1-010XGDC alloy;
vely small demagnetization factor of the Metglas-SA1-010XGDC
alloy.
is proportional to the piezomagnetic and piezoelectric oeffi
cients and inversely proportional to the demagnet-actor, a high
sensitivity is characteristic of the Metglas/omposites. The maximum
31 value obtained in the etglas-SA1-MP4010XGDC laminate was 400 mV
cm 1 kHz frequency and H DC = 3 Oe.
er, as it was found that the depolarization effect is occur in
polymers such as PVDF, the effect of two
poling processes were investigated in the ME proper-VDF hexafl
uoropropylene (PVDF-HPFP)/Metglas lami- ] After applying the
so-called conventional poling, usu- in the poling of piezoelectric
polymers [ 124 ] or cycling
125 ] In the fi rst, a D.C. electric fi eld ranging from 100 to
/m was applied to the sample during 300 s at room ture. Regarding
the second poling method, starting at tric fi elds, the sample is
cycled through many loops onsistent behavior is indicated. Higher
fi elds are then until the desired stable polarization is achieved.
Com-oth methods, it was verifi ed a shift of the ME peak ( agnetic
fi eld) of one method with respect to the other, d to the variation
of the boundary conditions of the striction of the Metglas. Since
the maximum peak is o the piezomagnetic coeffi cient of Metglas,
the varia-magnetostrictive vibration will result in the variation
agnetostrictive coeffi cient as well in a shift of the pie-
etic coeffi cient peak. In this case, variation in the max-f the
values with different poling processes is due to that conventional
poling uses DC electric fi eld, while ling employs an AC electric
fi eld, which produces dif-ientation stresses in the dielectric
polymer. The highest ined was 12 V cm 1 Oe 1 at 5 Oe and is lower
than the btained for the previously discussed PVDF/Metglas s,
however it has the advantage of allowing the change agnetic DC fi
eld at witch is obtained through modifi ca-
the poling process (electric fi eld strength and type of
el approach to high performance ME polymer compos- presented
with the chain-end cross-linked ferroelectric rFE)/Metglas 2605 SA1
composites. [ 126 ] The perform-
provement is due to the introduction of chain-end cross-nd
polysilsesquioxane structures into the P(VDF-TrFE) hich leads to
the formation of larger crystalline samples sequently better
piezoelectric response in comparison of pristine P(VDF-TrFE)
copolymers. With better piezo-properties a higher is expected. For
the cross-linked rFE)/Metglas laminate an 31 value of 17.7 V cm 1
Oe 1
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3380
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wileyon
FEATU
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was awherundevaluefurthof 65largeto a wtric la
Lethis with magnsinglmagnorthofor Mthe trMetgstrainants
rystal
PVwere shapewith
Table 2. Comparison of the main characteristics of the developed
polymer-based magnetoelectric materials.
Type
Nanoc
Polyme
LaminConstitution
omposite PE/Fe 3 O 4
PE/Nickel
P(VDF-TrFE)/Ni 0.5 Zn 0.5 Fe 2 O 4
P(VDF-TrFE)/CoFe 2 O 4
P(VDF-TrFE)/CoFe 2 O 4
r as a binder composites PVDF/Terfenol-D/PZT
PEO/Terfenol-D/PZT
Li + -PEO/Terfenol-D/PZT
PMMA/Terfenol-D/PZT
ate PVDF/Terfenol-D/PZT
PVDF/Terfenol-D/PZT
Spurr epoxy/Terfenol-D/PZT
PE/PVDF/Fe 3 O 4
VER/Terfenol-D/PZT
PZT/Terfenol-D/epoxy
Gd crystal/P(VDF-TrFE)/silver conductive epoxy
PVDF/Metglas unimorph
PVDF/Metglas three-layer
PVDF/Metglas
PVDF/Metglas
PVDF-HPFP/Metglaslinelibrary.com 2013 WILEY-VCH Verlag GmbH
& Co
V cm 1
of 5.1 kThis inME lamfor reallaminakind ofi.e., a tcrystal the
ferrpreparea silvercontactwas obamplituexploiti
As athe maordered
3. App
Based orials inare read
chieved under a DC magnetic fi eld of 3.79 Oe at 20 Hz, eas the
value obtained for the pristine P(VDF-TrFE)/Metglas r the same
conditions is 31 = 6.9 V cm 1 Oe 1 . The 31 s for cross-linked
P(VDF-TrFE)/Metglas laminates can be er improved to 383 V cm 1 Oe 1
at a resonance frequency kHz. The later laminate composite not only
shows the st value of in polymer-based ME materials but also points
ay to improve the piezoelectric properties of the piezoelec-yer and
hence the ME response. aving behind the ME PVDF based/Metglas
composites, laminated polymeric ME materials section is concluded
the large ME response from mechanically mediated etic fi
eld-induced strain effect in a PVDF/Ni 50 Mn 29 Ga 21
e crystal. [ 75 ] Ni 50 Mn 29 Ga 21 single crystal shows giant
DC etic fi eld induced strains of 610% in the tetragonal and
rhombic martensitic phases, which has attracted interest E
applications. [ 127 ] Showing obvious differences from
aditional magnetostrictive phases (Terfenol-D, ferrites or las),
the mechanism of the giant magnetic fi eld-induced s is due to the
reorientation of the martensitic twin vari-
under an applied magnetic fi eld as a result of magnetoc-line
anisotropy. [ 128,129 ] DF/Ni 50 Mn 29 Ga 21 single crystal
bilayered composites produced by adhering one layer of the
ferromagnetic memory alloy to one layer of the piezoelectric
polymer a conductive silver epoxy. The largest value 33 of 1.24
Cross-linked P(VDF-TrFE)/Metglas 2605
PVDF/Ni 50 Mn 29 Ga 21 H DC-Max. ME [Oe]
Ref. [mV cm 1 Oe 1 ]
resonance [mV cm 1 Oe 1 ]
0 [ 92 ] 11.4
0 [ 92 ] 6
5000 [ 50 ] 0.1 1.35
2500 [ 42 ] 4.1 41.3
2000 [ 51 ] 40
2000 [ 72 ] 42
1400 [ 109 ] 1.3
3.2
4.8
4000 [ 110 ] 80 3000
4000 [ 111 ] 300 6000
504 [ 113 ] 400 1100
2000 [ 114 ] 753
666 [ 117 ] 2700
3000 [ 119 ] 1310 2790
200 [ 131 ] 500
8 [ 73 ] 7200 238000
310000
8 [ 74 ] 21460
3 [ 9 ] 400
5 [ 76 ] 12000 . KGaA, Weinheim
Oe 1 obtained at 1 kHz and at an optimal magnetic fi eld Oe was
experimentally and theoretically confi rmed. [ 28 , 130 ]
vestigation not only reported a different constitution in inates
but also created a distinct physical mechanism
izing such effect. An alternative concept in ME poly mer ted
composites is based on thermal mediation. [ 131 ] This MF material
uses the large magnetocaloric effect (MCE), emperature change
induced in the ferromagnetic Gd by a magnetic fi eld and a large
pyroelectric response in oelectric P(VDF-TrFE) (68/32 mol%).
Composites were d by bonding a Gd crystal plate to the P(VDF-TrFE)
with conductive adhesive epoxy to ensure a good thermal between the
layers. An value of 0.5 V cm 1 Oe 1 tained at 293 K in an AC fi eld
of 2.4 Hz and 120 Oe de. The was further enhanced to 0.9 V cm 1 Oe
1 by ng the magnetic fl ux concentration effect. [ 132 ] conclusion
from this section, the results obtained for in polymer-based ME
material are shown in Table 2 by composite type.
lications
n the previous sections it is concluded that ME mate- general
and polymer-based ME materials in particular y for technological
applications. Promising applications
4 [ 126 ] 17700 383000
5100 [ 75 ] 1240
Adv. Funct. Mater. 2013, 23, 33713385
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3381
www.afm-journal.dewww.MaterialsViews.com
wileyonlinelibrary.comCH Verlag GmbH & Co. KGaA,
Weinheim
FE
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ay
3.2. Ene
The ever decreasing power requirement of electronic sensors and
devices [ 150 ] has attracted attention to energy harvesting
tech-nologies. [ 151 ] In particular, there has been signifi cant
interest in the area of the vibration energy based on piezoelectric
and magnetic harvesters. [ 152155 ] After the fi rst hypothesis of
ME materials as energy harvesting devices [ 156 ] some studies have
been reported in this area. As described in the previous section,
there have been signifi cant advances made in improving the
include magnetic fi eld sensors, transducers, fi lters,
devices,others. [ 5
polymerpolymeribility, lin someto advanhighligh
3.1. Fou
To meeefforts ahigher sstate (0 tunnel jsandwicsuch juof the
mmemoryThe codby detecprocess,high menergetithe manan electrthis
kinis the esor the mreading
A foucomposis widelyelectric layer of tion/maapplicatiof the
rethe PZTical stateand 11
A disref. [ 141(TbCo 2 (5teristic ctuator (from e mag-netost
etic ele-ment switch magn
A p e stable positio er posi-tion. T nce the inform e made using
ions [ 142 ] have c ls were
Adv. Fun 2013 WILEY-V
was deposited onto a commercial piezoelectric a Piezomechanik
Gmbh.). As a result of the inversrictive effect, the effective
anisotropy of the magnwas controlled by the applied voltage and
used toetization from one state to the other. ositive voltage sets
the magnetization in one of thns, whereas a negative voltage sets
it in the othhe position is kept when no voltage is applied.
Siation is stored magnetically, the readout can bmagnetoresistive
techniques. Theoretical calculatonfi rmed that the properties of
existing materia
ct. Mater. 2013, 23, 33713385compatscale. Wper laydevicesstrong
increas
As trelated netic/dthe fututhe submemorhappenas a bimeric
mplicity, capacityusuallyevaporamemornear futhe pol
Sinceinformacient isfi eld, sbility othe liteof 30 mperatura
detailferent asummathem cmemor
Figure 6 . Representation of a
oscillators, phase shifters, memory and biomedical materials,
among , 13 ] In some of these applications ic based ME materials,
due to the s unique characteristics such as fl ex-ightweight,
versatility, low cost and cases biocompatibility can be taken tage.
Some of these applications are ted as follows.
r State-Memory
t the intense demand of multimedia storage many re being made to
develop storage technologies with torage speed and density. [
133,134 ] In the traditional two and 1) memories, the memory
element is a magnetic unction that consists on an insulating tunnel
barrier hed by two magnetic electrodes. [ 135 ] The resistance of
nctions strongly depends on the relative orientation
agnetic moments, which is used to determine the state (0 or 1)
from the two magnetic electrodes. [ 136 ] ed magnetic bits can then
be read out nondestructively ting such resistance changes, however,
in the writing the magnetic bits are usually encoded by the use of
agnetic fi elds which is a process relatively slow and cally
expensive. [ 3 ] These problems can be solved with ipulation of the
magnetization direction by the use of ic fi eld, [ 137 ] taking
advantage of the ME effect. [ 58 , 138 ] For
d of multi-state memory ( Figure 6 ) the multiferroicity sential
factor for the information storage while the ME
agnetodielectric effect [ 139 ] is the mechanism for the and
writing procedure. [ 140 ] r-state memory cell based on the ME
PZT/Co bilayer
ite [ 140 ] has been already proposed. Co was used since it used
in magnetic recording and PZT due to its ferro-
properties. The composite was obtained by gluing one PZT to one
layer of Co with an epoxy. The polariza-
gnetization of such composite can be controlled by the on of
magnetic and electric fi elds and the combination mnant
ferroelectric polarization and magnetization in
/Co bilayer memory cell exhibits the desired four phys-s.
Results gave clear four-state signals of 15.8, 4.4, 5.5, .3 V,
which demonstrated the feasibility of the design. tinct room
temperature ME memory was presented in ] in which a magnetoelastic
nanostructured multilayer nm)/FeCo(5 nm)) with the required
uni-axial charac-ATU
RE A
RTIC
LE
ible with the realization of such a device at the nanometer ith
the reduction of size, densities up to 40 Gbits cm 2 r can be
expected for low energy, nonvolatile memory Given the very low
expected power, such a device is a ontender for vertical
integration of several layers, quickly ng the memory density. [
141,142 ] e current electronic market demands are intimately
to the use of fl exible materials, [ 143 ] not only the
mag-electric properties of materials will play a key role in re but
also their mechanical properties. [ 144 ] In this way, stitution of
PZT by a polymer in bilayer four-state ME ies will meet these new
challenges. Contrary to what ed a few decades ago, when polymers
were just used der in memory devices, [ 145,146 ] devices based on
poly-aterials are now a interesting topic due to their sim-ood
scability, low-cost, 3D stacking capability, and large for
data-storage. [ 147 ] These electroactive polymers are deposited by
ink-jet printing, spin-coating, or vacuum tion on a variety of
substrates for the fabrication of ies. [ 148 ] In this way,
polymers, may also acquire in the ture a more central status in the
memory market due to meric four-state ME memory devices. static
magnetic and electric fi elds are used for writing tion in the
four-state ME memories and the ME coeffi -used for reading with the
help of a small bias magnetic ch coeffi cient is determining in the
practical applica-
this new kind of memories. It was already reported in ature that
materials with ME coeffi cients in the order V cm 1 Oe 1 can be
used as components of room tem- four-state memory prototypes. [ 149
] Accordingly, and after d analysis of the ME coeffi cients
obtained from the dif-pproaches for preparing polymer-based ME
composites rized in Figure 9, it is possible to verify that almost
all of n be used in the development of this kind of multi-state
.
rgy Harvesting
four states memory based on ME materials.
-
3382
www.afm-journal.dewww.MaterialsViews.com
wileyo
FEATU
RE
ARTI
CLE
magnwill A comay methmicr
Thlamindens100 is unharveTerfePZT/vibranetica struit to the
P
Inwerea rar121 This harvemult
AnPZT/was wavedynasonicverteworkthe tthe vthe cIn thnetwthe
weratofor p255the efi eld
power consumption of 75 mW for a duration of 620 ms.
Despite all these developments, the next generation of
energy-harvesting applications, such as wearable energy-harvesting
systems, may require the piezoelectric materials to be fl exible,
lightweight, and even biocompat-ible. [ 163 ] In this way, ME
materials based on piezoelectric polymers may be an interesting
approach to meeting these requirements due to their fl exibility,
versatility, and low cost. [ 164 ] Some of the above reported ME
coef-fi cients on polymer-based ME materials are of the same order
of magnitude as the best
Figuritude of the ME coeffi cient of laminate composites, which
improve the ME energy harvesting effi ciency ( Figure 7 ). mbined
magnetic and vibration energy harvesting device be implemented on
silicon using the thin fi lm deposition ods and fabrication process
fl ow and combination with the o-machining technique. [ 157 ] e
energy harvesting in the Terfenol-D/PZT/Terfenol-D ate composites
has been reported to provide an energy
ity of 2.0 mW per cubic inch with vibrations of 21 Hz and mg. [
158 ] Furthermore, a windmill based on this approach
der development. [ 159 ] Ceramic based laminates energy sting
materials constituted by PZT/CoFe 2 O 4 and PZT/nol-D have been
also reported. [ 160162 ] In the case of the CoFe 2 O 4 energy
harvester, magnetically forced extensional tions of laminated
plates with piezoelectric and piezomag- layers were theoretically
analyzed. It was shown that such cture can be used to harvest
magnetic energy and convert
electric energy. The theoretical ME coeffi cient reported for
ZT/CoFe 2 O 4 energy harvester was 2.5 V Oe 1 . more experimental
work, ME PZT/Terfenol-D laminates placed between an oscillating
spherical steel bearing and e-earth magnet (NdFeB) to produce a
peak rms power of W from an rms host acceleration of 61 mG at 9.8
Hz. [ 162 ] approach may be useful in the future for kinetic energy
sting for applications where the host accelerations are
iaxial. electromagnetic energy harvesting scheme by using the
Terfenol-D transducer and a power management circuit presented in
ref. [ 161 ] . In such a transducer, the vibrating induced from the
magnetostrictive Terfenol-D in the mic magnetic fi eld converges
using a Bebronze ultra- horn. Consequently, more vibrating energy
can be con-d into electricity by the PZT. A switching capacitor
net- for storing electricity was also reported. The output of
ones obinvestigemergenharvesti
3.3. Mag
MagnetEarly apToday, mmore unetic fi
esensitivsystemstoresistitations. that direof large( Figure
FollowpolymerME senelectroncontainiPZT anNi 0.5 Zn 0sensor crial
withwas follME senPZT/TerME sen
e 7 . Representation of the ME energy harvesting mechanism.
nlinelibrary.com 2013 WILEY-VCH Verlag GmbH & Co. KGaA,
Weinheim
ransducer charged the storage capacitors in parallel until
oltage across the capacitors reached a threshold, and then
apacitors were automatically switched to being in series. is way,
more capacitors can be employed in the capacitor ork to further
raise the output voltage in discharging. For eak magnetic fi eld
environment, an active magnetic gen-
r and a magnetic underground coil antenna were used roducing an
ac magnetic fi eld of 0.21 Oe at a distance of 0 m. In combination
with the supply management circuit, lectromagnetic energy harvester
under an AC magnetic of 1 Oe can supply power for wireless sensor
nodes with Figure 8 . Representation of the ME magnetic fi eld
sensing mechanism.
Adv. Funct. Mater. 2013, 23, 33713385tained in the ME materials
that are already being used/ated as energy harvesters, and this
will encourage the ce of the next generation of polymer-based ME
energy-
ng materials.
netic Field Sensors
ic sensors have been in use for well over 2000 years. plications
were for direction fi nding in navigation. [ 165 ] agnetic sensors
are also used in navigation but many
ses have evolved. The technology for sensing mag-lds has also
evolved driven by the need for improved
ity, smaller size, and compatibility with electronic . [ 166 ]
Traditional magnetic sensors like Hall or magne-ve sensors need
power supply, which raises some limi-In this context, self-powered
magnetic fi eld sensors ctly transfer magnetic energy into electric
signals are
interest and can be realized thanks to the ME effect 8 ). [ 167
]
ing the suggestion by Nan et al. [ 63 ] to use ferroelectric
s/rare-earthiron alloys composites, such as magnetic
sors in radioelectronics, optoelectronics, and microwave ics and
transducers, magnetoelectric bulk composites ng 95 wt% of
yttrium-iron garnet and 5 wt% of lead d multilayer composite
material consisting of PZT and
.5 Fe 2 O 4 were used for sensor applications. [ 168 ] The ME
omprised a disk or plate from the magnetoelectric mate- two
electrodes for connecting to the voltage meter. This owed by
numerous reports about PZT based magnetic sors; [ 167172 ] vortex
magnetic fi eld sensor based ring-type fenol-D sensors, [ 170 ]
PZT/(Fe 80 Co 20 ) 78 Si 12 B 10 laminates sor for microtesla
sensitivity [ 167 ] and the effect of the
-
www.afm-journal.dewww.MaterialsViews.com
FEA Acknowledgements The aut(FCT) foNMed-SThe aut2010 Euthe
suppmodifi edentries i
mutual inductance on the magnetic fi eld sensitivity of the ME
PZT/Metglas laminate, [ 172 ] respectively.
The low fl exibility, cost, and fragility of PZTs [ 173,174 ] do
not meet the challenges of future sensor applications, [ 175,176 ]
there-fore multiferroic and ME polymer-based composites are
pos-sible successful alternatives for the more traditional ceramic
based ME magnetic sensors. [ 42 , 44 , 50 ] In this way, the ME
lami-nates of Metglas/PVDF magnetic fi eld sensors were
experimen-tally studied in ref. [ 177 ] and the performance was
compared to the prediction from a theoretical analysis. The fi eld
sensi-tivity and signal-to-noise ratio (SNR) of ME laminates were
also investigated. The results indicate that increasing the
electrode area (number of layers) of PVDF can enhanced the fi eld
sen-sitivity and SNR. This work has introduced a fi gure of merit
to characterize the overall infl uence of the piezolayer properties
on the SNR and has shown that newly developed piezoelectric single
crystals of PMN-PT and PZN-PT have potential to reach very high SNR
for ME magnetic sensors. The results also show that the ME coeffi
cients which are presently used to compare the ME materials
developed may not be relevant when using thes
Tpoterentthroital man
4. C
In cresetainappTabthe the fl expolypart
[ 1 ] L. Pe
[ 2 ] G. [ 3 ] W. [ 4 ] M [ 5 ] C.
Ap
Figucoef
Adv. 2013 WILEY-VCH Verlag GmbH & Co.
e ME materials for magnetic sensors. his new kind of ME magnetic
sensors also have enormous ntial as by-products related to magnetic
sensors: electric cur- sensors, speed sensors, angular sensors,
electronic steering, ttle control, battery management, vehicle
transmission, dig-compasses, and GPS devices [ 165 ] are just some
examples and y of them are already being studied. [ 170 , 178,179
]
onclusions
onclusion, polymer-based ME materials are a promising arch fi
eld with large interest for applications that cer-ly will appear
soon. The results obtained from the different roaches for preparing
such composites are presented in le 2 and summarized in Figure 9 .
The obtained values of magnetoelectric coeffi cients as well as the
broad range of magnetic fi eld at which they respond, together with
the
ibility, robustness and ease of fabrication related to the
mer-based materials, allow a large range of applications, in icular
in the fi elds of sensors and actuators.
[ 6 ] J. M [ 7 ] H.
05 [ 8 ] Y.-
Q. A. 20
[ 9 ] X. 20
[ 10 ] J. v [ 11 ] C. [ 12 ] M.
& [ 13 ] J. F [ 14 ] N.
sit [ 15 ] L.
ali [ 16 ] K.
Mo [ 17 ] M.
an [ 18 ] R.
Ac [ 19 ] S.
Pre [ 20 ] D.
Un [ 21 ] K.
Un [ 22 ] G.
lis [ 23 ] R.
Stu [ 24 ] T.
no [ 25 ] H. [ 26 ] E.
ym [ 27 ] .
cat [ 28 ] G.
Mare 9 . Distribution of the maximum polymer-based
magnetoelectric fi cient ( ) by reference, type and DC magnetic
Field at maximum.
Funct. Mater. 2013, 23, 33713385 3383wileyonlinelibrary.comKGaA,
Weinheim
TURE A
RTIC
LE
hors acknowledge the Foundation for Science and Technology r fi
nancial support through PTDC/CTM/69316/2006, NANO/D/0156/2007 and
PTDC/CTM-NAN/112574/2009 projects. hors also thank the support from
the COST Action MP1003, ropean Scientifi c Network for Artifi cial
Muscles. P.M. thanks ort of the FCT (grant SFRH/BD/45265/2008).
This article was after online publication. Article numbers were
added to the
n the reference section.
Received: September 25, 2012 Revised: November 28, 2012
Published online: March 5, 2013
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