Journal of Magnetism and Magnetic Materials 393 (2015) 8–14

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Journal of Magnetism and Magnetic Materials

http://d0304-88

n CorrE-m

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journal homepage: www.elsevier.com/locate/jmmm

Synthesis and characterization of polyaniline-hexaferrite composites

Tooba Khursheed a, M.U. Islam a,n, M. Asif Iqbal a,b, Irshad Ali a,n, Abdul Shakoor a,M.S. Awan c, Aisha Iftikhar a, Muhammad Azhar Khan d, Muhammad Naeem Ashiq e

a Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistanb College of E & ME, National University of Science and Technology, Islamabad, Pakistanc Center for Micro and Nano Devices Department of Physics, COMSATS Institute of Information Technology, Islamabad, Pakistand Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistane Institute of Chemical Science, Bahauddin Zakariya University, Multan 60800, Pakistan

a r t i c l e i n f o

Article history:Received 7 March 2014Received in revised form25 March 2015Accepted 8 May 2015Available online 9 May 2015

Keywords:PANI-hexaferrite compositesDielectric constantComplex permittivityDc resistivity

x.doi.org/10.1016/j.jmmm.2015.05.00853/& 2015 Elsevier B.V. All rights reserved.

esponding authors.ail addresses: dr.misbahulislam@bzu.edu.pk (Mibzu@gmail.com (I. Ali).

a b s t r a c t

Polyaniline was synthesized by chemical polymerization using aniline as monomer, and Y-type hex-aferrite with composition (Co2Mn2Sr1.66Nd0.4Fe10O22) was prepared by co-precipitation assisted by sur-factant. Three composites of Polyaniline with different ferrite ratios were prepared by mechanicalblending. The synthesized samples were characterized by X-Ray diffraction, Scanning electron micro-scopy and electrical measurements. The XRD analysis reveals that no second phase was observed inY-type hexagonal ferrite. In PANI-Ferrite composites, significant changes in resistivity, real and imaginarypart of complex permittivity were observed with the increase of ferrite in the polyaniline matrix. At lowfrequencies the magnitude of dielectric constant and complex permittivity is high with few relaxationpeaks. AC conductivity of PANI-Ferrite composites increase with the increase of frequency followingJonscher law. The resistivity and activation energy were found to show similar behavior.

& 2015 Elsevier B.V. All rights reserved.

1. Introduction

Ferrite Polymer Composites (FPC) is a mixture of ferrite powderand polymer with prime mechanical and magnetic propertiessusceptible for injection molding and other innovative applica-tions. Composite materials with magnetic fillers dispersed in apolymer matrix constitute a system with innovative physical andchemical properties. These properties are dependent on filler-polymer characteristics; filler concentration as well as mutual or-ientation of the filler particles [1]. Recently, there is a growingdemand for multifunctional composites to meet the future re-quirements of electronic components. Ferrite-Polymer composites(FPC) have attracted much attention due to their flexibility, tun-able properties, and easy processibility [2]. Polyaniline (PANI) hasattracted much attention because of its several unique propertiessuch as structural, physical, and electrochemical properties. It ishighly stable in air and soluble in various solvent, and exhibitsdramatic changes in its electronic structure and physical proper-ties at protonated state. It also shows magnetic behavior becauseof its high spin density [3,4]. Polymer based composites withelectroconductive properties have been used in numerous high

.U. Islam),

technology applications in organic light emitting diodes (OLED),polymer solar cells, sensors, energy storage, electro-optical deviceswireless communication, satellite television, heating systems andelectromagnetic shielding [4–6]. The Y-type hexaferrites haveelectrical and magnetic properties close to soft ferrites. Y-typehexaferrites are used in air traffic control and Global NavigationSatellite Systems (GNSS) broadcasting navigational signals in var-ious bands between about 1.2–1.6 GHz. Y-type hexaferrites are alsoused in chip electronic components (MLCI, MLCB), compact phaseshifter devices and electromagnetic interference suppression [7,8].

In this paper Y-type hexagonal ferrite with nominal composi-tion Co2Mn2Sr1.66Nd0.4Fe10O22 was used as filler in PANI matrix.Three composites FP1 (25 wt% of ferrite), FP2 (50 wt% of ferrite)and FP3 (75 wt% of ferrite) were synthesized and characterized forthe EMI shielding effectiveness and microwave absorbing deviceapplications.

2. Materials and methods

2.1. Synthesis of Polyanilline

Polyaniline was prepared by chemical Polymerization 0.5 molof aniline monomer was dispersed in 100 ml of deionized water.The solution was kept on a magnetic stirrer and 5 mol of the hy-drocholoric acid (HCl) dissolved in 200 ml deionized water was

0 10 20 30 40 50 60 70 80 90

110

1 1

211

2 14

0 0

30

Inte

nsity

(a.u

)

2 Theta (degree)

PANI

FP1

FP2

FP3

Ferrite

018 11

011

6 119

0 2

10

1 0

19 1 0

22

1 1

211

2 14 1 0

280

0 30

1 1

91

1 6

1 0

28

0 2

4 0

2 10

Fig. 1. X-ray Diffraction patterns of Plyaniline, FP1, FP2, FP3 and Y-type hexaferrite(Co2Mn2Sr1.66Nd0.4Fe10O22).

T. Khursheed et al. / Journal of Magnetism and Magnetic Materials 393 (2015) 8–14 9

added drop wise under vigorous stirring for one and half hours,where as 0.6125 mol of the oxidant ammonium per sulfate (APS)was added drop wise under vigorous stirring, the color of themixture changes and the reaction mixture was kept at roomtemperature for one day. Finally the suspension was filtered andwashed. The greenish paste of polyaniline was obtained and driedunder sunlight for 2–3 h. The basic structure of polyaniline isshown below, it comprises of alternatively (–B–NH–B–NH–) unitswhere B represent benzenoid state with chemical formula C6H4.

2.2. Synthesis of ferrite

The starting materials used in the synthesis of Y-type hexa ferriteswere Fe(NO3)3 �9H2O (Riedel-de Haen, 97%), Co(NO3)2 �6H2O (Merck,499%), Sr(No3)2 (Merck, 99%), MnCl2 �3H2O (Merck, 499%),Nd2O3(Merck, 99%), CTAB (Merck, 97%) as a surfactant, NH3 (FisherScientific, 35%) as a precipitating agent and methanol as washingagent. The Y-type hexaferrite sample with nominal composition(Co2Mn2Sr1.66Nd0.4Fe10O22) were prepared by co-precipitation assistedby surfactant (microemulsion). The metallic salt solution of the re-quired molarities were prepared in deionized water and mixed in a100 ml beaker. The solution was stirred on the magnetic hot plate at60 °C and CTAB was added. The temperature was than removed and2ml of NH3 solution was then added under constant stirring thatresulted in the formation of precipitates. The precipitates were washedwith deionized water several times and finally washed with methanol.The precipitates were dried in an oven at 120 °C for 12 h and finallysintered at 1050 °C for 8 h.

2.3. Synthesis of composites

Three ferrite-polymer composites were prepared by blendingpolyaniline powder with (Co2Mn2Sr1.66Nd0.4Fe10O22) nano-particles indifferent ratios that is FP1 (25 wt% of ferrite), FP2 (50 wt% of ferrite)and FP3 (75 wt% of ferrite). Thorough grinding was carried out in anagate mortar and pestle. The ground powders of composite materialswere pressed into the disk shaped pellets of thickness 2.4–2.7 mmunder the load of 25 KN using the hydraullic press.

2.4. Experimental setup

The X-ray diffraction patterns were recorded using a computercontrolled XRD JDX3532. JEOL, Japan, operated at 1200W. The radia-tions used were Cu-Kα (λ¼1.5406 Å) and each sample was scanned in2θ range from 10 to 75°. JSM-5910 scanning electron microscope wasused for investigating the surface morphology of the samples. Thepermittivity of the samples was measured using Agilent impedanceanalyzer model E4991 A RF. The electrical resistivity was measured bytwo probe method using Keithly source meter model 2400.

3. Results and discussion

3.1. X-ray diffraction

XRD patterns of the synthesized samples are shown in Fig. 1. XRDpatterns of (Co2Mn2Sr1.66Nd0.4Fe10O22) Y-type hexaferrite were com-pared with JCPDS card no. 00-019-019-0100. XRD patterns revealedwell defined single phase Y-type hexagonal ferrite structure where asPANI shows amorphous structure. There is co-existence of PANI and(Co2Mn2Sr1.66Nd0.4Fe10O22) phases in the composite sample as in-dicated in the XRD patterns. The peaks of (Co2Mn2Sr1.66Nd0.4Fe10O22)

were observed in all the compositions of polyaniline composites,which designate the presence of crystalline filler ferrite particles in thepolymer matrix. The intensity of peaks in composites decreases be-cause of amorphous behavior of PANI [5]. The crystallite size of Y-typehexaferrite filler was calculated from XRD pattern by using the wellknown Scherer formula [9];

D k cos/ 1Bλ β θ= ( )

where k is the shape constant having value 0.89 for hexagonal system,λ is the wavelength of CuKα radiations (1.5406 Å), β is the broadeningof the diffraction line measured at half width of maximum intensityand θB is the Bragg’s angle of diffraction. Estimated crystallite size offerrite is 52.84 nm. All the peaks of ferrite filler were indexed andlattice parameters a, c and volume of unit cell for ferrite and compo-sites were calculated by using the relations (2) and (3) [12].

Sin a h hk k c l/3 /4 22 2 2 2 2 2 2 2( ) ( )θ λ λ= + + + ( )

V a c0.8666 32= ( )

The calculated values of lattice parameters and volume of unitcell are tabulated in Table 1. The results show that the latticeconstants a and c are in the good agreement with the reportedresults for Y-type hexagonal ferrites.

3.2. Scanning electron microscopy (SEM)

Fig. 2 shows the SEM images of (a) Ferrite(Co2Mn2Sr1.66Nd0.4Fe10O22) (b) PANI (c)FP1 (d) FP2 and (e) FP3. It canbe seen that the Y-type haxagonal ferrite show homogenous structurewith haxagonal platlets. PANI has porous and irregular surface but asthe ferrite content is increased the surface morphology changes. Fer-rite particles are found embedded in PANI matrix. PANI-Ferrite com-posites exhibits two phase systemwhere the bright phase correspondsto the ferrite and darker phase is PANI.

3.3. Dielectric properties

3.3.1. Dielectric constantThe dielectric constant (ε′) was calculated by using the for-

mula;

Cd A/ 40ε ε′ = ( )

Fig. 3 shows the variation of dielectric constant as a function offrequency for PANI that occurs in three regimes. In regime I, strongpolarization occurs due to the presence of polaron/bipolaron andother bound charges, which leads to high value of ε′ and ε″ at low

Table 1Lattice parameters, cell volume, dielectric constant, complex part of dielectric constant resistivity and product ε′ ρ 1/2 of PANI-Ferrite and composites.

Sample a(Å) c(Å) c/a V(Å3) ε′ at 1 GHz ε″ at 1 GHz ρ1/2(ohm-cm)1/2 ε′ ρ1/2(ohm-cm)1/2

PANI – – – – 3132.17 3443.08 1.03 2.32 �1012

Ferrite 5.94 43.80 7.36 1341.83 249.89 250.62 653.41 1.63 �1014

FP1 5.97 43.51 7.28 1349.93 2285.28 1958.96 9.44 2.15 �1013

FP2 5.98 43.45 7.26 1347.34 1333.57 693.99 16.88 2.25�1013

FP3 5.98 43.52 7.27 1343.84 863.79 403.66 69.56 6.00 �1013

T. Khursheed et al. / Journal of Magnetism and Magnetic Materials 393 (2015) 8–1410

frequency. In regime II with the increase of frequency, the dipolescannot reorient themselves along with the applied electric fieldand as a result dielectric constant decreases [10,11]. In regime III,at further higher frequency the ε′ values of PANI are almost con-stant and low with same reason that the dipoles present in systemcannot reorient themselves along with applied electric field till2.5 GHz. Above 2.5 GHz anomalous dispersion is observed.

In Fig. 3 it can be seen that amongst all the samples, the lowerdielectric constant value is observed for the Y-type hexagonalferrite as compared to PANI due to insulating nature of the ferrite.The dielectric constant exhibit the usual behavior of ferrites inaccordance with Maxwell Wegner model [23]. The high value of

Fig. 2. SEM Image of (a) Ferrite, (b) P

dielectric constant at low frequency is due to interfacial polariza-tion. The ferrite grains which are conductive as compare to grainboundaries are effective at high frequency where as resistive grainboundaries are effective at low frequencies. The hopping fre-quency of electron between Feþ2 and Feþ3 ion at octahedral sitesfollows the applied electric field at low frequencies and hence thedielectric constant is large. At high frequencies the dipoles do notfollow the applied frequency. The lower value of dielectric con-stant is most likely to be caused by intrinsically low dielectric losstangent (tan δ) of ferrite powder [11–13].

In case of a ferrite-polymer composite (FPCs), the contributionto dielectric constant and dielectric loss also occur due to

ANI, (c) FP1, (d) FP2 and (e) FP3.

0.0 5.0x108 1.0x109 1.5x109 2.0x109 2.5x109 3.0x1090

2000

4000

6000

8000

10000

12000

14000

16000

Ferrite(1) 75% Ferrite FP3(2) 50% Ferrite FP2(3) 25% Ferrite FP1(4) PANI(5)

Die

lect

ric c

onst

ant

Frequency(Hz)

FerriteFP3FP2

FP1

PANI

Fig. 3. Plot of the dielectric constant vs. frequency of ferrite(Co2Mn2Sr1.66Nd0.4Fe10O22), FP1, FP2, FP3 and Plyaniline.

Fig. 4. Variation of the dielectric loss vs. frequency of ferrite(Co2Mn2Sr1.66Nd0.4Fe10O22), FP1, FP2, FP3 and Plyaniline.

0.0 5.0x108 1.0x109 1.5x109 2.0x109 2.5x109 3.0x109

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Ferrite 75% Ferrite FP3 50% Ferrite FP2 25% Ferrite FP1(4) PANI

tan δ

Frequency (Hz)

Ferrite

FP3FP2FP1

PANI

Fig. 5. The tangent loss vs. frequency of ferrite (Co2Mn2Sr1.66Nd0.4Fe10O22), FP1,FP2, FP3 and Plyaniline.

T. Khursheed et al. / Journal of Magnetism and Magnetic Materials 393 (2015) 8–14 11

interfacial polarization and its relaxation as the PANI-ferrite par-ticles separated by insulating matrix molecules giving rise toheterogeneity [8]. With the increase of ferrite in polyaniline ma-trix, significant decrease in real and imaginary part of complexpermittivity was observed as shown in Table 1. The low value ofdielectric constant is observed for the FP2 and FP3 which showsthe similar ferrite like behavior at lower frequencies and executesfew resonance peaks at higher frequencies due to undampeddipoles.

The higher values of dielectric constant and dielectric loss forFP1 observed due to the difference in the relative dielectric con-stant of ferrite and the polyaniline which results in the accumu-lation of more space charge, and strong orientation polarizationthat consequently leads to the improved values of microwaveabsorption. Moreover it can be observed that as PANI content inFP1 (25 wt% of ferrite) is larger than ferrite content so in FP1predomination is shown by PANI and in FP3 (75 wt% of ferrite)predomination is shown by Y-type ferrite particles [14]. The peaksat a frequency fZ2.69 GHz for all the samples shows the re-sonance phenomena [15].

3.3.2. Dielectric lossFig. 4 shows the variation of dielectric loss vs. frequency for all

the samples. In polyaniline strong polarization occurs due to thepresence of polaron/bipolaron and other bound charges, that leadsto high value of ε′ and ε″ at low frequency as shown in Fig. 4. Theincrease of polaron/bipolaron hopping results in the local dis-placement in a direction of external applied field causes an in-crease in the polarization and thus enhances the dielectric loss.With the increase in frequency, the dipoles present in the systemcannot reorient themselves with the applied electric field and as aresult dielectric loss also decreases [4]. A resonance may occurwhen the frequency of electron hopping ωi equals the appliedfrequency ω, resulting in extra peaks at 2.65 GHz for all thesamples in ε′, ε″ and tangent loss. The ε″ follows ε′ and showsimilar behavior. In composites high value of dielectric loss in alow frequency band imparts high shielding effectiveness due tothe presence of a large quantity of polarizable dipoles dispersed ina non conducting ferrite matrix [21]. The loss spectra of PANI-Ferrite composites shows extra peaks suggesting the presence ofrelaxing dipoles and non-relaxing dipole in the composites [22].The resonance phenomena at frequency fZ2.69 GHz is alsoobserved.

The loss tangent was calculated, tan δ¼ ε″/ ε′ as shown inFig. 5 as a function of frequency.

Loss tangent for all the samples follows the same behavior as

that of ε″ with frequency due to the same reasons as discussed.

3.3.3. Ac conductivityAc conductivity of all the samples was calculated by the for-

mula

f2 5ac 0π ε εб = ″ ( )

Fig. 6(a, b) shows the plot of AC conductivity versus frequencyfor ferrite, FP1, FP2 and FP3, pure PANI. It can be observed that forferrite бac increases with increase of frequency linearly. The Acconductivity curve of pure PANI is shown in Fig. 6(b). It can be seenthat variation of conductivity by increasing frequency exists threeregimes: it increases in regime I (1.9�107r fr2.14 MHz), almostunchangeable in regime II (2.14 MHzr fr3.23 MHz) and de-creases in regime III (3.23 MHzr f r1.55 GHz). Conductivity in-creases at low frequency due to the contribution of polarons/bi-polarons bond in the direction of applied field. High dielectric lossof PANI due to presence of a high quantity of polarizable dipolesdispersed in a direction of applied field results in high conductivity

8.0 8.5 9.0 9.5 10.0 10.5

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

logσ

(ohm

-cm

)-1

logω (Η )

Ferrite 75% Ferrite FP3 50% Ferrite FP2 25% Ferrite FP1

FP1

FP2

FP3

Ferrite

8.0 8.5 9.0 9.5 10.0 10.5

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

Regime III

Regime II

Regim

e I

logσ

(ohm

-cm

)-1

logω (Η )

PANI

Fig. 6. (a) AC conductivity vs. frequency plot of Ferrite, FP1, FP2 and FP3. (b) ACconductivity vs. frequency of Polyaniline.

0 20 40 60 80 100

0

2

4

6

8

10

12

14

lnρ(

ohm

-cm

)

Ferrite Content (wt %)

PANI

FP1

FP2

FP3

Ferrite

Fig. 7. Plot of resistivity vs. ferrite content in PANI.

T. Khursheed et al. / Journal of Magnetism and Magnetic Materials 393 (2015) 8–1412

which is in region I, it become constant in regime II as polarons/bipolarons bond come into equilibrium and decrease with increaseof frequency is due to the fact that hopping between the ions couldnot follow the applied field frequency and it lags behind it.

AC conductivity increases with the increase of frequency inpure PANI as well as its Ferrites composites, following a power lawwith exponent s¼0.99�1.475. The strong dispersion of the con-ductivity can be approximated by an empirical power law, whichhas been termed by Jonscher as ‘universal power law’ [16,17]. Theclass of materials that show similar behavior in the AC con-ductivity is large, including amorphous semiconductors, organicsemiconductors, ionic conducting glasses, ceramics, ionic or elec-tronic conducting polymers, metal cluster compounds, transitionmetal oxides, etc. The phenomenon is common to both electronand ion conducting materials. The (real part of the) dynamicconductivity can be described by a power law:

A 6acsσ ω= ( )

where A is the pre-exponential factor. In the vast majority of

disordered materials exponent s lies between 0 and 1 althoughoccasionally s has been found larger than unity [18].

An exponent greater than 1 as has been observed in the fre-quency dependence curve of AC conductivity in our conductingpolymer and ferrite composites can be explained on the basis of arecent relaxation mode theory of quasi-Debye response of hoppingconduction [20] in terms of extended non-diffusing mode whichhas been shown to give rise to an exponent greater than 1 whichtends to 2 with increasing temperature [19].

3.4. Resistivity measurement

3.4.1. Room temperature resistivityRoom temperature electrical resistivity of Polyaniline, Y-type

hexa-ferrite CoMnSr1.6Nd0.4Fe12O22 and PANI-Ferrite composites(FP1,FP2 and FP3) is plotted in the Fig. 7. At room temperature, theresistivity of PANI (ρ¼1.06Ω-cm) is very low but as the ferritecontent is varied from 25 wt%, 50 wt% and 75 wt%, the resistivityof composites increases from 8.92�101�4.8�103 (Ω-cm) andthe resistivity of ferrite is 4.2�105 (Ω-cm). The increased re-sistivity in composites may be due to particle blockage of con-duction path by ferrite nanoparticles embedded in the PANI ma-trix. In case of FP3 as the PANI content in the composites is low-ered, the change in compactness becomes more significant. Withthe increase of ferrite content the free particles or ions joinedfirmly together increasing the compactness that is effect of grainboundary become stronger [10].

3.4.2. Relationship between dielectric constant and resistivityThe values of dielectric constant and resistivity are given in

Table 1. It can be seen from the table that the dielectric constantapproximately inversely proportional to the square root of re-sistivity for all the samples. The product ε′(ρ)1/2 remains nearlyconstant as shown in Table 1 [23]. The decrease in dielectricconstant with increase in ferrite contents is attributed to increasein resistivity of the ferrite samples. The role of microstructure(grain boundary, porosity, etc.) is very decisive for the discussionof resistivity and dielectric behavior.

3.4.3. Temperature dependent resistivityTemperature dependent resistivity of these samples was mea-

sured in the temperature range of 303–453 K. Fig. 8 shows that dc

2.2 2.4 2.6 2.8 3.0 3.2 3.4

-2

0

2

4

6

8

10

12

14

lnρ(

ohm

-cm

)

103/T(K)

PANI

FP1

FP2

FP3

Ferrite

Fig. 8. Arrhenius plot for Hexaferrite, FP1, FP2, FP3 and Polyaniline.

0 20 40 60 80 100

0.0

0.1

0.2

0.3

0.4

0.5

activ

atio

n en

ergy

Ea(

eV)

Ferrite content (wt %)

PANI

FP1FP2

FP3

Pure Ferrite

Fig. 9. Plot of activation energy (Ea) vs. ferrite content in PANI.

T. Khursheed et al. / Journal of Magnetism and Magnetic Materials 393 (2015) 8–14 13

resistivity decreases linearly with temperature for all the samples.This can be attributed to the increase in drift mobility of thermallyactivated charge carriers. The observed decrease in dc resistivitywith temperature is normal behavior for ferrite which resemblewith semiconducting behavior which follows the Arrhenius rela-tion:

exp E k T/ 7a B0 ( )ρ ρ= ( )

where the symbols has usual meaning. The conduction is due toboth type of charges that is due to the mobility of electrons andholes. The mobility of holes increase with temperature as it in-volves the thermal activation process and as result the resistivitystarts to decrease. The decrease in resistivity with the increase oftemperature for the synthesized materials is in agreement withalready reported results [24].

3.4.4. Activation energyThe activation energies were obtained from the slope of the

Arrhenius plots in accordance with Eq. (6). Fig. 9 shows that theactivation energy and the electrical resistivity show similar beha-vior as a function of ferrite filler composition. The samples withhigher resistivity have higher values of activation energies andvice versa. The higher values of activation energy at higher ferriteconcentration show strong blocking of the conduction mechanism

is due to ferrite nanoparticles embedded in PANI matrix.

4. Conclusions

�

The XRD results shows that the PANI-Ferrite phases co-existswhich is the characteristic of composites.

�

The dielectric constant decreases with the increase of ferritecontent in PANI this is useful for the applications of thesematerials in multilayer chip inductors, core materials for softelelctromagnets with an added advantage of flexibility.

�

The ac conductivity shows that the hopping is the likely con-duction mechanism in composites as indicated by the exponentvalues in power law.

�

The decrease in ac conductivity in composites may be attrib-uted to the conformal changes in PANI and increase indisorderliness.

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