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MWCNTs nanocomposites
Accepted Manuscript Title: Influence of multi-walled carbon nanotubes (MWCNTs) volume percentage on the magnetic and microwave absorbing properties of BaMg0.5 Co0.5 TiFe10 O19 /MWCNTs nanocomposites Author: Reza Shams Alam Mahmood Moradi Hossein Nikmanesh PII: DOI: Reference:
S0025-5408(15)30118-5 http://dx.doi.org/doi:10.1016/j.materresbull.2015.09.016 MRB 8406
To appear in:
MRB
Received date: Revised date: Accepted date:
23-3-2015 11-8-2015 11-9-2015
Please cite this article as: Reza Shams Alam, Mahmood Moradi, Hossein Nikmanesh, Influence of multi-walled carbon nanotubes (MWCNTs) volume percentage on the magnetic and microwave absorbing properties of BaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites, Materials Research Bulletin http://dx.doi.org/10.1016/j.materresbull.2015.09.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Influence of multi-walled carbon nanotubes (MWCNTs) volume percentage on themagnetic and microwave absorbing properties ofBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites
Reza Shams Alama, MahmoodMoradia,b,*, HosseinNikmanesha
a
Physics Department, College of Sciences, Shiraz University, Shiraz 71946-84795, Iran.
b
Institute of Nanotechnology, Shiraz University, Shiraz 71454, Iran.
*
Corresponding author: MahmoodMoradi ([email protected]).
Graphical abstract
Reflection losses of (a) doped barium hexaferrite, BaMg0.5Co0.5TiFe10O19, sample and their nanocomposites with (b) 4 vol. (c) 8 vol. and (d) 12 vol. % of MWCNTs are presented. Highlights
BaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites were synthesized.
The structural, magnetic and microwave absorption properties were investigated.
The microwave absorption is strongly influenced by volume percentage of MWCNTs.
The nanocomposite with 8 vol. % of MWCNTs can be proposed as a wideband absorber.
1
Abstract In this studyBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites with differentamount of MWCNTs (0, 4, 8 and 12 vol. %) were synthesized. Here, the X-raydiffraction (XRD), Fourier transform spectroscopy (FTIR) and scanning electronmicroscopy (SEM) were used to demonstrate the structural and morphologicalcharacteristics of the prepared samples. XRD along with FTIR examinations exhibited that the nanocomposites were successfully synthesized. Vibrating sample magnetometer (VSM)showed the relatively strong dependence of saturation magnetization and coercivityon the volume percentage of MWCNTs. The microwave evaluation also confirmedthat the complex permittivity of nanocomposites could be enhanced by addingMWCNTs. Finally, the nanocomposite with 8% vol. of MWCNTs exhibited thebest microwave absorption performance among the samples.
KEYWORDS: A. magnetic materials, A. composites, A. nanostructures, B. magnetic properties, B. chemical synthesis
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1. Introduction Recent developments in microwave absorber technology have incorporated toproducing materials that effectively reduce electromagnetic signals reflections withreasonable physical performance.Depending on whether they are suitable for lowor high frequency applications, a variety of absorber materials exist that canbe used to suppress electromagnetic interference (EMI) [1-6]. In general, microwaveabsorber materials can be divided into magnetic and dielectric absorbers. Thisclassification is according to the materials lossy fillers that are related to magneticand dielectric loss characteristics, respectively [7-9]. The Mtype bariumhexaferrite (BaM) powders are known to be ideal fillers to develop electromagneticabsorber materials at microwave frequency. The reason behind that are low cost,low density, high stability, large electrical resistivity and high magnetic loss in themicrowave frequencies. However, negligible (poor) dielectric loss has limited theirapplications [10-14].Nowadays, many attempts are being made to develop absorber composites consisting ofboth dielectric and magnetic fillers. These fillers are expected to have dielectricand magnetic loss simultaneously [8,11]. Among the materials that could be usedas dielectric loss fillers, multi-walled carbon nanotubeshave attracted much attention due to their high aspect ratio, unique electrical properties, and especiallytheir large permittivity at microwave frequencies [15,16]. The outstanding propertiesof MWCNTs, 3
together with barium hexaferrite nanoparticles, could be veryinteresting for practical applications [17,18]. Due to their high permeability andpermittivity losses, BaM/MWCNTs composites can be used in fabricating highfrequencymicrowave absorbing materials [19,20]. Regarding working frequency range, there are two key factors to be consideredin preparing a potential ferrite/MWCNTs composites microwave absorber. Thefirstis finding a ferrite composition with a reasonable microwave absorption rateas the base magnetic material, and the second is optimizing the volume percentageof MWCNTs in the composites. There are a variety of ferrite compositions whichcan to be used as the base magnetic absorber material in different frequency ranges[2123]. The present study tries to concentrate on the influence of MWCNTsvolume percentage to improve magnetic and microwave characteristics ofBaMg0.5Co0.5TiFe10O19/MWCNTsnanocomposites. As proposed in previousresearch [13] and because of its reasonable absorption performance in Kufrequency band, BaMg0.5Co0.5TiFe10O19hexaferrite, was selected as thebase magnetic absorber.
2. Experimental procedure 2.1. Preparation of doped barium hexaferrite nanoparticles
4
Mg+2, Co+2and Ti+4substituted barium hexaferrite nanoparticles wereprepared by a co-precipitation method. At the beginning, to form a homogenoussolution, the stoichiometric amounts of MgCl2.2H2O, CoCl2.6H2O, TiCl4and FeCl3 were dissolved in deionized water at 70oC and stirred to form a homogenoussolution. Then, 2 wt. % of poly vinyl alcohol (PVA) was added to the solution as asurfactant. Afterward, the pH of the solution was adjusted slowly to 13 by addingdrop wise alkaline sodium hydroxide (NaOH, 1.5M) solution. The resulted gel waswashed with deionized water for several times until a solution with neutral pH wasobtained. Next, the suspension was filtered and dried at 100oC. Finally, theobtained powder was sintered at 950oC for 2h.
2.2. Preparation of BaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites The pristine multi-walled carbon nanotubes were dispersed into a solution ofconcentrated nitric acid, and treated with sonication for 1.5 h, and dried at 90°C.Then, appropriate amounts of the dried MWCNTs (4, 8 and 12 vol. %) weredispersed in a mixture of the acrylic acid and distilled water, and dispersed againfor 30 minutes. After that, BaMg0.5Co0.5TiFe10O19nanoparticles were added to theabove mixture by employing sonication for 1.5 h. And finally, the solution wasdried at 90°C for further use.
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2.3. Characterization study A diffractometer was applied using Cu-Kα radiation to determine the Xraydiffraction (XRD) patterns of the samples. The formation of nanocomposites wasalso confirmed by Fourier transform infrared (FTIR) spectroscopy. Then, ascanning electron microscopy (SEM) was used to determine the morphologicalstudy. After that, the magnetic property of the prepared samples was examinedusing a vibrating sample magnetometer (VSM) at room temperature. A vectornetwork analyzer also was employed to determine the microwave properties of thesamples. To this end, the composite specimens were prepared by mixing theprepared samples and epoxy resin with the weight percentage of 70:30, and thenpressing them to form a toroidal-shape with the inner diameter of 3 mm, outerdiameter of 7 mm, and a thickness of 2 mm.
3. Results and discussion 3.1. The structural and morphological evaluation The XRD patterns of the functionalized MWCNTs, doped barium hexaferritenanoparticles and BaMg0.5Co0.5TiFe10O19/MWCNTsnanocomposites with 4, 8 and12 vol. % of MWCNTs are shown in Fig. 1. The diffraction peak appears at 26.4 oin the figure with an index of (002) corresponds to the MWCNTs, 6
which indicatesthat the structure of functionalized multi-walled carbon nanotube is notdeteriorated after an acid treatment process. Based on the standard XRD data [14]and according to Fig. 1(b), the single phase M-type structure was formed in thedoped hexaferrite sample without any secondary phases or impurities.Additionally, it was well indicated in Figs. 1(c) to 1(e) that the related diffractionpeaks of MWCNTs and BaMg0.5Co0.5TiFe10O19nanoparticles were appearedtogether in the X-ray patterns of BaMg0.5Co0.5TiFe10O19/MWCNTsnanocomposites, implying that the nanocomposites were synthesized successfully.
The FTIR spectrums of functionalized MWCNTs, doped hexaferrite sampleand BaMg0.5Co0.5TiFe10O19/MWCNTsnanocomposite with 8 vol. % of MWCNTsare shown in Fig. 2. The FTIR spectroscopy has been used to identify the nature ofchemical bonds of the prepared samples. Fig. 2 (a) shows the FTIR spectra offunctionalized MWCNTs. Here, two peaks, in the range of 2700-3000 cm-1, areattributed to the characteristics of the C–H stretching vibrations. And also the peakat 1768 cm-1is assigned to the carbonyl (C=O), the stretching mode in the acidpretreated MWCNTs that indicates successful production of –COOH groups on thesidewall of MWCNTs [15-18]. The other peak at 1382 cm-1corresponds to the C–O stretching vibration [16,17], while the absorption peaks in the area 7
between 400cm-1and 800 cm-1in Figs. 2(b) and 2(c) are related to the Fe-O stretching vibrationbond in octahedral and tetrahedral sites of hexaferrite structure, respectively[14,17]. In Fig. 2(c), the peak at 1585 cm-1is related to the C=C stretchingmode associated with MWCNTs sidewall defects [17-19]. There is a peak ataround 1626 cm-1in all the spectrums which is assigned to water trace in the KBrused to make the pellet sample for FTIR analysis [17]. The peak at 1729 cm1
shown in Fig. 2(c) can be related to the stretching mode of the carbonylgroups
(C=O) [17,18]. In addition, in all spectra, the peaks appeared at around of2922 cm1
and 3445 cm-1belong respectively to C–H stretching and O–Hstretching vibrations
[18]. The FTIR spectrums of nanocomposites with 4 and 12vol. % of MWCNTs, which are not presented here, show the same trend asindicated in Fig.2(c) for the sample with 8 vol. % of MWCNTs.
The morphological images ofpristine MWCNTs, doped barium hexaferritenanoparticles andBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites are shown inFig. 3. Asindicated in Fig. 3(a), the MWCNTs have rather smooth surfaces withan entangledmorphology. Fig. 3(b) also shows that the BaMg0.5Co0.5TiFe10O19nanoparticles arealmost homogenous with an average particle size below 100 nm,although thenanoparticles are agglomerated. The magnetic interactions betweennanoparticlesmay be attributed to their 8
agglomeration. The SEM images of nanocomposites withdifferent percentage of MWCNTs are depicted in Figs. 3(c) to(e). Looking at thefigures, it can be seen that MWCNTs are well dispersed in thenanocomposites. Inaddition, a large number of the doped barium hexaferritenanoparticles aredeposited along the outer side of functionalized MWCNTs in aclosed-packedarrangement. The distribution of doped hexaferrite nanoparticles onthe externalsurface of MWCNTs is relatively uniform. Actually, the ferritenanoparticles can beabsorbed on MWCNTs surface like a layer due to thepresence of the surfaceactive groups, such as –COOH, which were formed in theacid treatment process[19,20].
3.2. Magnetic characteristics The VSM graphs of BaMg0.5Co0.5TiFe10O19nanoparticles andBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites are shown in Fig. 4. It is wellknown that pristine MWCNTs contain residual metals such as Ni nanoparticles thatare used in the CVD technology [17]. Therefore, the ferromagnetic trend with verysmall saturation magnetization could be observed in the hysteresis loop ofMWCNTs [17]. The hysteresis loops show that the values of saturationmagnetization (Ms) of BaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites are lowerthan that of the doped hexaferrite sample. This can be attributed to the existence of MWCNTs as a phase with a very low saturation magnetization, 9
structural distortion in the surface of hexaferrite nanoparticles caused by the interaction of the transition metal ions with the oxygen atoms in the magnetoplumbite structure, and also the strain between hexaferrite nanoparticles and surface of MWCNTs [16-19].It is also appeared that the coercivity (Hc) is decreased by increasing the volume percentage of MWCNTs. Actually, active groups on the sidewall ofMWCNTs are attributed to oriented aggregation of hexaferrite nanoparticles [16,19]. The number of these active centers increases by increasing the volume percentage of MWCNTs; as a result, the orientation degree of nanocomposite increases[16]. Moreover, the surface magnetic anisotropy of hexaferrite nanoparticles can be reduced in the interface of MWCNTs and nanoparticles which may decrease of the coercivity [16,18].It is well known thatthe surface ofhexaferritenanoparticles is rough and contains inhomogenities such as porosityand cracks [17].After decorating the side wall of MWCNTs by the hexaferritenanoparticles, theeffects of some of these inhomogenities may be reduced, thething that leads to thereduction of coercivity [16-18].
3.3. Microwave characteristics 3. 3. 1. Complex permittivity
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In general, the complex permittivity (j) represents the dielectricpropertyof a material subjected to an electromagnetic field. The real part () is ameasure ofthe storage capacity of electric energy, while the imaginary part () istherepresentation of the loss of electrical energy [21]. It is well known that theenhancement of microwave absorption of ferrite/MWCNTs composites is mainlyrelated to the improvement of permittivity [21-23]. Here, the frequencydependence of complex permittivity of doped barium hexaferrite sample (j) and nanocomposite (j, with 8 vol. % of MWCNTswereinvestigated and compared, the results are shown in Fig. 5(a). It is wellindicated inthe figure that the real part of permittivity, for the doped bariumhexaferritesample, reflects insignificant variation in the whole frequency rangestudied in thepresent work. In addition, the imaginary part of the hexaferritesample permittivityis relatively small. This is a normal behavior exhibited byhexaferrites which isalso reported by other researchers [24,25]. Generally, thecomplex permittivity ofhexaferrites is mainly due to the ionic polarization,intrinsic polarization andinterfacial polarization [24]. As expected, the real andimaginary parts of thecomplex permittivity increase with raising the volumepercentage of MWCNTs. Inaddition, both the real and imaginary parts of theBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposite decrease with increasingfrequency, while exhibiting a visible frequency-dependence dielectric 11
response.The obtained results are consistent to the other research works as well [21,26].The enhancement of complex permittivity here can mainly be ascribed to dielectricpolarization and relaxation effects [23,26]. The MWCNTs with excellent electricalconductivity and high aspect ratios can easily form conducting networks within aferrite matrix [27,28]. The conducting networks would interact and attenuate theelectromagnetic radiation effectively. Then, it can be concluded that thepermittivity characteristic of insulating doped hexaferrite sample can be tailoredeffectively and simply by adding MWCNTs. It should also be mentioned that thecomplex permittivity of ferrite/MWCNTs nanocomposites is sensitive to thevolume concentration of MWCNTs [17]. It is useful to evaluate the electric loss tangent (=/) in order to investigate theeffect of MWCNTs on the microwave absorption performance. Hence, the values ofelectric loss tangent of BaMg0.5Co0.5TiFe10O19sample and nanocomposite with 8vol. % of MWCNTs are shown in Fig. 5(b). It is well indicated in the figure thatthe electric loss tangent of nanocomposite with 8 vol. % of MWCNTs isrelatively higher than that of doped hexaferrite sample. It is also worth mentioningthat the increasing electric loss tangent factor could not be the one and the onlyreason for excellent microwave absorption performance, because the concept ofmatched impedance is another important parameter relating to reflection loss [26]. 12
3. 3. 2. Microwave absorption characteristic Based on the transmission line theory, reflection loss (RL) is a function of thenormalized input impedance, Zin, and can be expressed as follows [2]: RL 20log ( Z in Z 0 ) / ( Z in Z 0 )
(1)
where Z 0 0 / 0 377 ,and Zin is given by: Z in Z 0 r / r tanh ( j 2 fd / c ) r r
(2)
In this equation, fequals the frequency of electromagnetic wave, d and c are thethickness ofabsorber layer and the velocity of light in vacuum, and finally ɛrand μrare thecomplex permittivity and complex permeability of the sample, respectively. Fig. 6 shows the reflection loss (RL) of the doped barium hexaferrite sampleand nanocomposites with different volume percentage of MWCNTs, at the thickness of 2mm.Here, the bandwidth is defined as the frequency width in which the reflection lossis more than -20 dB.From Fig. 6, it is obvious that there are two resonance absorption peaks in the RL curves of all the samples. The resonance absorption at low frequency range is related to domain wall, while the peak at high frequency is related to natural ferromagnetic resonance [14,17]. The natural resonance frequency of the hexaferrite is related to anisotropy field (Ha) as follows[14]: f r Ha
(3)
13
where γ is the gyromagnetic ratio.Generally, the undoped barium hexaferrite has a natural resonance frequency about 48 GHz due to its strong uniaxial anisotropy along the c-axis[18]. Findings of the present study proved that the anisotropy field could be controlled by substituting a proper amount of Mg-Co-Tications for Fe+3ions in the hexaferrite structure, causing the resonance to be shifted to the lower frequencies [18,28].It is known that the anisotropy field is contingent to coercivity [14]. Hence, a decrease in coercivity by increasing the amount of MWCNTs in the nanocomposite (see Fig. 4)causes the natural resonance frequency to shift to lower frequency range, as shown in Fig. 6. Fig. 6(a) exhibits anabsorption peak around -34 dB at the matching frequency of 18.5 GHz for the doped barium hexaferrite sample, and also there is another matching frequency at 16.2 GHz with reflection loss of -26.3 dB. The bandwidth which is covered by this sample is about 3.4 GHz.It is known that microwave absorptioncharacteristic could be improved in the case of ferrite/MWCNTs because of better matching between the dielectric and magnetic losses [2123].However, the concentration of MWCNTs plays a key role on the microwave absorbing performance [17,21].Figs. 6(b) and (c) indicate that with an increase in carbonnanotube content in the nanocomposite (up to 8 vol. %), the bandwidth coupled withreflection loss values increase.The maximum reflection loss increases from -34 dB fordoped barium hexaferrite sampleto more than -40 dB for 14
nanocomposite with 4 and 8 vol. % of MWCNTs.Furthermore, the bandwidth which can be covered by thenanocomposite with 4 and 8 vol.% of MWCNTs are about 4.3 GHz and 5.5 GHz, respectively. In fact, the presence of MWCNTs may cause extra dissipation because of the polarization and relaxation processes [23,26]. Furthermore, by increasing the concentration of MWCNTs, when electromagnetic waves travel inside the material, there would be more additional interfaces leading to multiple scattering [27]. This effect is favorable to widening absorption bandwidth [27,28].Fig. 6(d) shows that with a further increase ofMWCNTs content to 12 vol. %, the absorption bandwidth and maximum reflectionloss decrease. This might be related to the aggregation of MWCNTs in higher thana special content or high electrical conductivity at high MWCNTsloading [23, 28].As a result, most of the electromagnetic waves are reflected on the surfaceof the absorber layer [28,29]. Based on the findings of the present study, it can beconcluded that the presence of an optimum percentage of MWCNTs is a vitalfactor to achieve the best microwave absorption performance.It can be inferred from the RL curves that the nanocomposite with 8 vol. % of MWCNTs exhibits the bestabsorbing performance as compared to the other samples.
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4. Conclusion In summary, BaMg0.5Co0.5TiFe10O19nanoparticles were prepared by acoprecipitationmethod, and successfully attached along the side wall of thefunctionalized multi-walled carbon nanotubes. As presented in VSM graphs, itcould be found that by adding MWCNTs into the composite, the saturationmagnetization decreases as well as the coercivity.In the reflectivity curves also, itis well indicated that the microwave absorptionperformance of nanocomposites can be optimized by adding a certain amount ofMWCNTs. Consequently, the nanocomposite with 8 vol. % of MWCNTs and athickness of 2mm, could be proposed as a potential microwave absorber materialwith many applications in the Ku-band. Here, the bandwidth which could becovered by this sample is about 5.5 GHz.Generally, the excellent electromagneticwave absorption of the nanocomposite is resulted from the efficient complementbetween the permittivity and permeability of materials. This characteristic leads toa better matching of the dielectric and magnetic losses. Either only the magnetic orelectric loss may induce a weak electromagnetic wave absorption property due tothe imbalance of the electromagnetic match.
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References [1] A. N. Yusoff, M. H. Abdullah, S. H. Ahmed, S. F. Jusoh, A. A. Mansor, S. A.A. Hamid, Electromagnetic and absorption properties of some microwaveabsorbers, J. Appl. Phys. 92 (2002) 876-882. [2] D. D. L. Chung, Electromagnetic interference shielding effectiveness of carbonmaterial, Carbon. 39 (2001) 297-285. [3] L. Wang, H. Yu, X. Ren, G. Xu, Magnetic and microwave absorptionproperties of BaMnxCo1−xTiFe10O19, J. Alloys Compd. 588 (2014) 212-216. [4] C. Dong, X. Wang, P. Zhou, T. Liu, J. Xie, L. Deng, Microwave magnetic and absorption properties of M-type ferrite Ba(TiCo)xFe12-2xO19in the Ka band, J.Magn. Magn.Mater. 354(2014) 340-344. [5] S. Ozah, N. S. Bhattacharya, Nanosized barium hexaferrite in novolancphenolic resin as microwave absorber for X-band application, J. Magn. Magn.Mater, 342(2013) 92-99. [6] T. Inui, K. Konishi, K. Oda, Fabrication of broad-band RF-absorber composedof planar hexagonal ferrites, IEEE Trans. Magn. 35(1999) 3148-3150. [7] Z. W. Li, Z. H. Yang, L. B. Kong, Y. J. Zhang, High-frequency magneticproperties at K and Ka bands for barium-ferrite/silicone composites, J. Magn.Magn.Mater. 325 (2013) 82-86. 17
[8] Y. B. Feng, T. Qiu, C. Y. Shen, Absorbing property and structural design of microwave absorber based on carbonyl iron and barium ferrite, J. Magn. Magn.Mater. 318 (2007) 8-13. [9] P. Saini, V. Choudhary, B. P. Singh, R. B. Mathur, S. K. Dhawan, Enhancedmicrowave absorption behavior of polyaniline-CNT/polystyrene blend in 12.4-18GHz range, Synth. Metals. 161(2011) 1522-1526. [10] L. Li, K. Chen, H. Liu, G. Tong, H. Qian, B. Hao, Attractivemicrowaveabsorbingproperties of M-BaFe12O19ferrite, J. Alloys Compd. 557 (2013) 11-17. [11] C. L. Yuan, Y. S. Tuo, Microwave adsorption of Sr(MnTi)xFe122xO19 particles,J.
Magn. Magn.Mater. 342 (2013) 47-53.
[12] M. K. Tehrani, A. Ghasemi, M. Moradi, R. Shams Alam, Widebandelectromagnetic wave absorber using doped barium hexaferrite in Kuband, J.Alloys compd. 509 (2011) 8398-8400. [13] R. Shams Alam, M. K. Tehrani, M. Moradi, E. Hosseinpour, A. Sharbati, Therole of matching thickness on the wide band electromagnetic wave suppresserusing single layer doped barium ferrite, J. Magn. Magn.Mater.323(2011) 1040–1043. [14] R. Shams Alam, M. Moradi, M. Rostami, H. Nikmanesh, R. Moayedi, Y. Bai,Structural, magnetic and microwave absorption properties of doped Ba18
hexaferritenanoparticles synthesized by co-precipitation method, J. Magn. Magn.Mater. 381(2015) 1-9. [15] Y. Li, Y. Huang, S. Qi, L. Niu, Y. Zhang, Y. Wu, Preparation, magnetic andelectromagnetic properties of polyaniline/strontium ferrite/multiwalled carbonnanotubes composite, Appl. Surf. Sci. 258 (2012) 3659-3666. [16] W. Wang, Q. Li, C. Chang, Effect of MWCNTs content on the magnetic andwave absorbing properties of ferrite-MWCNTs composites, Synth. Metals161(2011) 44-50. [17] G. R. Gordani, A. Ghasemi, A. Saidi, Optimization of carbon nanotubesvolume percentage for enhancement of high frequency magnetic properties ofSrFe8MgCoTi2O19/MWCNTs, J. Magn. Magn.Mater. 363 (2014) 4954. [18] M. Asghari, A. Ghasemi, E. Paimozd, A. Morisako, Evaluation of microwaveand magnetic properties of substituted SrFe12O19 and substituted SrFe12O19/multiwalledcarbon nanotubes nanocomposites, Mater.Chem. Phys. 143 (2013)161-166. [19] D. Shi, J. P. Cheng, F. Liu, X. B. Zhang, Controlling the size and size distribution of magnetite nanoparticles on carbon nanotubes, J. Alloys Compd. 502 (2010) 365-370. [20] Q. Zhang, M. Zhu, Q. H. Zhang, Y. Li, H. Wang, The formation of magnetite 19
nanoparticles on the sidewalls of multi-walled carbon nanotubes, Compos. Sci.Technol. 69 (2009) 633-638. [21] G. Liu, L. Wang, G. Chen, S. Hua, C. Ge, H. Zhang, R. Wu, Enhancedelectromagnetic absorption properties of carbon nanotubes and zinc oxide whiskermicrowave absorber, J. Alloys Compd. 514 (2012) 183-188. [22] S. L. Shi, J. Liang, The effect of multi-walled carbon nanotubes onelectromagnetic interference shielding of ceramic composites, Nano. Technol. 19 (2008) 25507. [23] F. Qin, C. Brosseau, A review and analysis of microwave absorption inpolymer composites filled with carbonaceous particles, J. Appl. Phys. 111 (2012) 06131. [24] X. Tang, Y. Yang, K. Hu, Structure and electromagnetic behavior ofBaFe12_2x(Ni0.8Ti0.7)xO19-0.8xin the2-12GHz frequency range, J. Alloy Compd. 477(2009) 488-492. [25] S. M. Abbas, A.K. Dixit, R. Chatterjee, T. C. Goel, Complex permittivity,complex permeability and microwave absorption properties of ferritepolymerComposites , J. Magn. Magn.Mater. 309 (2007) 20-24.
20
[26] T. Zhang, D. Huang, Y. Yang, F. Kang, J. Gu, Fe3O4/carbon compositenanofiber absorber with enhanced microwave absorption performance, Mater. Sci.Eng B. 178 (2013) 1-9. [27] A. Ghasemi, S. Javadpour, X. Liu, A. Morisako, Magnetic and reflection losscharacteristics of substituted barium ferrite/functionalized multiwalled carbonnanotube, IEEE. Trans. Magn. 47 (2011) 4310-4313. [28] A. Ghasemi, S. E. Shirsath, X. Liu, A. Morisako, A comparison betweenmagnetic and reflection loss characteristics of substituted strontium ferrite andnanocomposites of ferrite/carbon nanotubes, J. App. Phys. 111 (2012) 07B543.[29] Y. Zhai, Y. Zhang, Y. Ren, Electromagnetic characteristic and microwaveabsorbing performance of different carbon-based hydrogenatedacrylonitrilebutadiene,Mater. Chem. Phys. 133 (2012) 176-181.
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Figure captions Fig. 1. The XRD patterns of (a) functionalized MWCNTs, (b) doped barium hexaferrite nanoparticles, c) nanocomposite with 4 vol. % of MWCNTs, d) nanocomposite with 8 vol. % of MWCNTs, and (e) nanocomposite with 12 vol. % of MWCNTs. Fig.2.FTIR spectrum of (a) functionalized MWCNTs, (b) doped barium hexaferrite sample, and (c) nanocomposite with 8 vol. % of MWCNTs.
Fig. 3.SEM images of (a) pristine MWCNTs, (b) doped barium hexaferrite nanoparticles, (c) nanocomposite with 4 vol. % of MWCNTs, (d) nanocomposite with 8 vol. % of MWCNTs, and (e) nanocomposite with 12 vol. % of MWCNTs.
Fig.4. Hysteresis loops of (a) doped barium hexaferrite nanoparticles, and nanocomposites with (b) 4 vol. % of MWCNTs, (c) 8 vol. % of MWCNTs, (e) 12 vol. % of MWCNTs. Fig. 5.(a) The real ( 1 ) and imaginary part ( 1 ) of complex permittivity of doped barium hexaferrite sample and that of nanocomposite ( 2 , 2 ) with 8 vol. % of MWCNTs, and (b) The values of electric loss tangent of doped barium hexaferrite sample and nanocomposite with 8 vol. % of MWCNTs. Fig. 6. Reflection loss of (a) doped barium hexaferrite sample and nanocomposites with (b) 4 vol. % of MWCNTs, (c) 8 vol. % of MWCNTs, and (d) 12 vol. % of MWCNTs.
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S0025-5408(15)30118-5 http://dx.doi.org/doi:10.1016/j.materresbull.2015.09.016 MRB 8406
To appear in:
MRB
Received date: Revised date: Accepted date:
23-3-2015 11-8-2015 11-9-2015
Please cite this article as: Reza Shams Alam, Mahmood Moradi, Hossein Nikmanesh, Influence of multi-walled carbon nanotubes (MWCNTs) volume percentage on the magnetic and microwave absorbing properties of BaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites, Materials Research Bulletin http://dx.doi.org/10.1016/j.materresbull.2015.09.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Influence of multi-walled carbon nanotubes (MWCNTs) volume percentage on themagnetic and microwave absorbing properties ofBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites
Reza Shams Alama, MahmoodMoradia,b,*, HosseinNikmanesha
a
Physics Department, College of Sciences, Shiraz University, Shiraz 71946-84795, Iran.
b
Institute of Nanotechnology, Shiraz University, Shiraz 71454, Iran.
*
Corresponding author: MahmoodMoradi ([email protected]).
Graphical abstract
Reflection losses of (a) doped barium hexaferrite, BaMg0.5Co0.5TiFe10O19, sample and their nanocomposites with (b) 4 vol. (c) 8 vol. and (d) 12 vol. % of MWCNTs are presented. Highlights
BaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites were synthesized.
The structural, magnetic and microwave absorption properties were investigated.
The microwave absorption is strongly influenced by volume percentage of MWCNTs.
The nanocomposite with 8 vol. % of MWCNTs can be proposed as a wideband absorber.
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Abstract In this studyBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites with differentamount of MWCNTs (0, 4, 8 and 12 vol. %) were synthesized. Here, the X-raydiffraction (XRD), Fourier transform spectroscopy (FTIR) and scanning electronmicroscopy (SEM) were used to demonstrate the structural and morphologicalcharacteristics of the prepared samples. XRD along with FTIR examinations exhibited that the nanocomposites were successfully synthesized. Vibrating sample magnetometer (VSM)showed the relatively strong dependence of saturation magnetization and coercivityon the volume percentage of MWCNTs. The microwave evaluation also confirmedthat the complex permittivity of nanocomposites could be enhanced by addingMWCNTs. Finally, the nanocomposite with 8% vol. of MWCNTs exhibited thebest microwave absorption performance among the samples.
KEYWORDS: A. magnetic materials, A. composites, A. nanostructures, B. magnetic properties, B. chemical synthesis
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1. Introduction Recent developments in microwave absorber technology have incorporated toproducing materials that effectively reduce electromagnetic signals reflections withreasonable physical performance.Depending on whether they are suitable for lowor high frequency applications, a variety of absorber materials exist that canbe used to suppress electromagnetic interference (EMI) [1-6]. In general, microwaveabsorber materials can be divided into magnetic and dielectric absorbers. Thisclassification is according to the materials lossy fillers that are related to magneticand dielectric loss characteristics, respectively [7-9]. The Mtype bariumhexaferrite (BaM) powders are known to be ideal fillers to develop electromagneticabsorber materials at microwave frequency. The reason behind that are low cost,low density, high stability, large electrical resistivity and high magnetic loss in themicrowave frequencies. However, negligible (poor) dielectric loss has limited theirapplications [10-14].Nowadays, many attempts are being made to develop absorber composites consisting ofboth dielectric and magnetic fillers. These fillers are expected to have dielectricand magnetic loss simultaneously [8,11]. Among the materials that could be usedas dielectric loss fillers, multi-walled carbon nanotubeshave attracted much attention due to their high aspect ratio, unique electrical properties, and especiallytheir large permittivity at microwave frequencies [15,16]. The outstanding propertiesof MWCNTs, 3
together with barium hexaferrite nanoparticles, could be veryinteresting for practical applications [17,18]. Due to their high permeability andpermittivity losses, BaM/MWCNTs composites can be used in fabricating highfrequencymicrowave absorbing materials [19,20]. Regarding working frequency range, there are two key factors to be consideredin preparing a potential ferrite/MWCNTs composites microwave absorber. Thefirstis finding a ferrite composition with a reasonable microwave absorption rateas the base magnetic material, and the second is optimizing the volume percentageof MWCNTs in the composites. There are a variety of ferrite compositions whichcan to be used as the base magnetic absorber material in different frequency ranges[2123]. The present study tries to concentrate on the influence of MWCNTsvolume percentage to improve magnetic and microwave characteristics ofBaMg0.5Co0.5TiFe10O19/MWCNTsnanocomposites. As proposed in previousresearch [13] and because of its reasonable absorption performance in Kufrequency band, BaMg0.5Co0.5TiFe10O19hexaferrite, was selected as thebase magnetic absorber.
2. Experimental procedure 2.1. Preparation of doped barium hexaferrite nanoparticles
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Mg+2, Co+2and Ti+4substituted barium hexaferrite nanoparticles wereprepared by a co-precipitation method. At the beginning, to form a homogenoussolution, the stoichiometric amounts of MgCl2.2H2O, CoCl2.6H2O, TiCl4and FeCl3 were dissolved in deionized water at 70oC and stirred to form a homogenoussolution. Then, 2 wt. % of poly vinyl alcohol (PVA) was added to the solution as asurfactant. Afterward, the pH of the solution was adjusted slowly to 13 by addingdrop wise alkaline sodium hydroxide (NaOH, 1.5M) solution. The resulted gel waswashed with deionized water for several times until a solution with neutral pH wasobtained. Next, the suspension was filtered and dried at 100oC. Finally, theobtained powder was sintered at 950oC for 2h.
2.2. Preparation of BaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites The pristine multi-walled carbon nanotubes were dispersed into a solution ofconcentrated nitric acid, and treated with sonication for 1.5 h, and dried at 90°C.Then, appropriate amounts of the dried MWCNTs (4, 8 and 12 vol. %) weredispersed in a mixture of the acrylic acid and distilled water, and dispersed againfor 30 minutes. After that, BaMg0.5Co0.5TiFe10O19nanoparticles were added to theabove mixture by employing sonication for 1.5 h. And finally, the solution wasdried at 90°C for further use.
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2.3. Characterization study A diffractometer was applied using Cu-Kα radiation to determine the Xraydiffraction (XRD) patterns of the samples. The formation of nanocomposites wasalso confirmed by Fourier transform infrared (FTIR) spectroscopy. Then, ascanning electron microscopy (SEM) was used to determine the morphologicalstudy. After that, the magnetic property of the prepared samples was examinedusing a vibrating sample magnetometer (VSM) at room temperature. A vectornetwork analyzer also was employed to determine the microwave properties of thesamples. To this end, the composite specimens were prepared by mixing theprepared samples and epoxy resin with the weight percentage of 70:30, and thenpressing them to form a toroidal-shape with the inner diameter of 3 mm, outerdiameter of 7 mm, and a thickness of 2 mm.
3. Results and discussion 3.1. The structural and morphological evaluation The XRD patterns of the functionalized MWCNTs, doped barium hexaferritenanoparticles and BaMg0.5Co0.5TiFe10O19/MWCNTsnanocomposites with 4, 8 and12 vol. % of MWCNTs are shown in Fig. 1. The diffraction peak appears at 26.4 oin the figure with an index of (002) corresponds to the MWCNTs, 6
which indicatesthat the structure of functionalized multi-walled carbon nanotube is notdeteriorated after an acid treatment process. Based on the standard XRD data [14]and according to Fig. 1(b), the single phase M-type structure was formed in thedoped hexaferrite sample without any secondary phases or impurities.Additionally, it was well indicated in Figs. 1(c) to 1(e) that the related diffractionpeaks of MWCNTs and BaMg0.5Co0.5TiFe10O19nanoparticles were appearedtogether in the X-ray patterns of BaMg0.5Co0.5TiFe10O19/MWCNTsnanocomposites, implying that the nanocomposites were synthesized successfully.
The FTIR spectrums of functionalized MWCNTs, doped hexaferrite sampleand BaMg0.5Co0.5TiFe10O19/MWCNTsnanocomposite with 8 vol. % of MWCNTsare shown in Fig. 2. The FTIR spectroscopy has been used to identify the nature ofchemical bonds of the prepared samples. Fig. 2 (a) shows the FTIR spectra offunctionalized MWCNTs. Here, two peaks, in the range of 2700-3000 cm-1, areattributed to the characteristics of the C–H stretching vibrations. And also the peakat 1768 cm-1is assigned to the carbonyl (C=O), the stretching mode in the acidpretreated MWCNTs that indicates successful production of –COOH groups on thesidewall of MWCNTs [15-18]. The other peak at 1382 cm-1corresponds to the C–O stretching vibration [16,17], while the absorption peaks in the area 7
between 400cm-1and 800 cm-1in Figs. 2(b) and 2(c) are related to the Fe-O stretching vibrationbond in octahedral and tetrahedral sites of hexaferrite structure, respectively[14,17]. In Fig. 2(c), the peak at 1585 cm-1is related to the C=C stretchingmode associated with MWCNTs sidewall defects [17-19]. There is a peak ataround 1626 cm-1in all the spectrums which is assigned to water trace in the KBrused to make the pellet sample for FTIR analysis [17]. The peak at 1729 cm1
shown in Fig. 2(c) can be related to the stretching mode of the carbonylgroups
(C=O) [17,18]. In addition, in all spectra, the peaks appeared at around of2922 cm1
and 3445 cm-1belong respectively to C–H stretching and O–Hstretching vibrations
[18]. The FTIR spectrums of nanocomposites with 4 and 12vol. % of MWCNTs, which are not presented here, show the same trend asindicated in Fig.2(c) for the sample with 8 vol. % of MWCNTs.
The morphological images ofpristine MWCNTs, doped barium hexaferritenanoparticles andBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites are shown inFig. 3. Asindicated in Fig. 3(a), the MWCNTs have rather smooth surfaces withan entangledmorphology. Fig. 3(b) also shows that the BaMg0.5Co0.5TiFe10O19nanoparticles arealmost homogenous with an average particle size below 100 nm,although thenanoparticles are agglomerated. The magnetic interactions betweennanoparticlesmay be attributed to their 8
agglomeration. The SEM images of nanocomposites withdifferent percentage of MWCNTs are depicted in Figs. 3(c) to(e). Looking at thefigures, it can be seen that MWCNTs are well dispersed in thenanocomposites. Inaddition, a large number of the doped barium hexaferritenanoparticles aredeposited along the outer side of functionalized MWCNTs in aclosed-packedarrangement. The distribution of doped hexaferrite nanoparticles onthe externalsurface of MWCNTs is relatively uniform. Actually, the ferritenanoparticles can beabsorbed on MWCNTs surface like a layer due to thepresence of the surfaceactive groups, such as –COOH, which were formed in theacid treatment process[19,20].
3.2. Magnetic characteristics The VSM graphs of BaMg0.5Co0.5TiFe10O19nanoparticles andBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites are shown in Fig. 4. It is wellknown that pristine MWCNTs contain residual metals such as Ni nanoparticles thatare used in the CVD technology [17]. Therefore, the ferromagnetic trend with verysmall saturation magnetization could be observed in the hysteresis loop ofMWCNTs [17]. The hysteresis loops show that the values of saturationmagnetization (Ms) of BaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposites are lowerthan that of the doped hexaferrite sample. This can be attributed to the existence of MWCNTs as a phase with a very low saturation magnetization, 9
structural distortion in the surface of hexaferrite nanoparticles caused by the interaction of the transition metal ions with the oxygen atoms in the magnetoplumbite structure, and also the strain between hexaferrite nanoparticles and surface of MWCNTs [16-19].It is also appeared that the coercivity (Hc) is decreased by increasing the volume percentage of MWCNTs. Actually, active groups on the sidewall ofMWCNTs are attributed to oriented aggregation of hexaferrite nanoparticles [16,19]. The number of these active centers increases by increasing the volume percentage of MWCNTs; as a result, the orientation degree of nanocomposite increases[16]. Moreover, the surface magnetic anisotropy of hexaferrite nanoparticles can be reduced in the interface of MWCNTs and nanoparticles which may decrease of the coercivity [16,18].It is well known thatthe surface ofhexaferritenanoparticles is rough and contains inhomogenities such as porosityand cracks [17].After decorating the side wall of MWCNTs by the hexaferritenanoparticles, theeffects of some of these inhomogenities may be reduced, thething that leads to thereduction of coercivity [16-18].
3.3. Microwave characteristics 3. 3. 1. Complex permittivity
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In general, the complex permittivity (j) represents the dielectricpropertyof a material subjected to an electromagnetic field. The real part () is ameasure ofthe storage capacity of electric energy, while the imaginary part () istherepresentation of the loss of electrical energy [21]. It is well known that theenhancement of microwave absorption of ferrite/MWCNTs composites is mainlyrelated to the improvement of permittivity [21-23]. Here, the frequencydependence of complex permittivity of doped barium hexaferrite sample (j) and nanocomposite (j, with 8 vol. % of MWCNTswereinvestigated and compared, the results are shown in Fig. 5(a). It is wellindicated inthe figure that the real part of permittivity, for the doped bariumhexaferritesample, reflects insignificant variation in the whole frequency rangestudied in thepresent work. In addition, the imaginary part of the hexaferritesample permittivityis relatively small. This is a normal behavior exhibited byhexaferrites which isalso reported by other researchers [24,25]. Generally, thecomplex permittivity ofhexaferrites is mainly due to the ionic polarization,intrinsic polarization andinterfacial polarization [24]. As expected, the real andimaginary parts of thecomplex permittivity increase with raising the volumepercentage of MWCNTs. Inaddition, both the real and imaginary parts of theBaMg0.5Co0.5TiFe10O19/MWCNTs nanocomposite decrease with increasingfrequency, while exhibiting a visible frequency-dependence dielectric 11
response.The obtained results are consistent to the other research works as well [21,26].The enhancement of complex permittivity here can mainly be ascribed to dielectricpolarization and relaxation effects [23,26]. The MWCNTs with excellent electricalconductivity and high aspect ratios can easily form conducting networks within aferrite matrix [27,28]. The conducting networks would interact and attenuate theelectromagnetic radiation effectively. Then, it can be concluded that thepermittivity characteristic of insulating doped hexaferrite sample can be tailoredeffectively and simply by adding MWCNTs. It should also be mentioned that thecomplex permittivity of ferrite/MWCNTs nanocomposites is sensitive to thevolume concentration of MWCNTs [17]. It is useful to evaluate the electric loss tangent (=/) in order to investigate theeffect of MWCNTs on the microwave absorption performance. Hence, the values ofelectric loss tangent of BaMg0.5Co0.5TiFe10O19sample and nanocomposite with 8vol. % of MWCNTs are shown in Fig. 5(b). It is well indicated in the figure thatthe electric loss tangent of nanocomposite with 8 vol. % of MWCNTs isrelatively higher than that of doped hexaferrite sample. It is also worth mentioningthat the increasing electric loss tangent factor could not be the one and the onlyreason for excellent microwave absorption performance, because the concept ofmatched impedance is another important parameter relating to reflection loss [26]. 12
3. 3. 2. Microwave absorption characteristic Based on the transmission line theory, reflection loss (RL) is a function of thenormalized input impedance, Zin, and can be expressed as follows [2]: RL 20log ( Z in Z 0 ) / ( Z in Z 0 )
(1)
where Z 0 0 / 0 377 ,and Zin is given by: Z in Z 0 r / r tanh ( j 2 fd / c ) r r
(2)
In this equation, fequals the frequency of electromagnetic wave, d and c are thethickness ofabsorber layer and the velocity of light in vacuum, and finally ɛrand μrare thecomplex permittivity and complex permeability of the sample, respectively. Fig. 6 shows the reflection loss (RL) of the doped barium hexaferrite sampleand nanocomposites with different volume percentage of MWCNTs, at the thickness of 2mm.Here, the bandwidth is defined as the frequency width in which the reflection lossis more than -20 dB.From Fig. 6, it is obvious that there are two resonance absorption peaks in the RL curves of all the samples. The resonance absorption at low frequency range is related to domain wall, while the peak at high frequency is related to natural ferromagnetic resonance [14,17]. The natural resonance frequency of the hexaferrite is related to anisotropy field (Ha) as follows[14]: f r Ha
(3)
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where γ is the gyromagnetic ratio.Generally, the undoped barium hexaferrite has a natural resonance frequency about 48 GHz due to its strong uniaxial anisotropy along the c-axis[18]. Findings of the present study proved that the anisotropy field could be controlled by substituting a proper amount of Mg-Co-Tications for Fe+3ions in the hexaferrite structure, causing the resonance to be shifted to the lower frequencies [18,28].It is known that the anisotropy field is contingent to coercivity [14]. Hence, a decrease in coercivity by increasing the amount of MWCNTs in the nanocomposite (see Fig. 4)causes the natural resonance frequency to shift to lower frequency range, as shown in Fig. 6. Fig. 6(a) exhibits anabsorption peak around -34 dB at the matching frequency of 18.5 GHz for the doped barium hexaferrite sample, and also there is another matching frequency at 16.2 GHz with reflection loss of -26.3 dB. The bandwidth which is covered by this sample is about 3.4 GHz.It is known that microwave absorptioncharacteristic could be improved in the case of ferrite/MWCNTs because of better matching between the dielectric and magnetic losses [2123].However, the concentration of MWCNTs plays a key role on the microwave absorbing performance [17,21].Figs. 6(b) and (c) indicate that with an increase in carbonnanotube content in the nanocomposite (up to 8 vol. %), the bandwidth coupled withreflection loss values increase.The maximum reflection loss increases from -34 dB fordoped barium hexaferrite sampleto more than -40 dB for 14
nanocomposite with 4 and 8 vol. % of MWCNTs.Furthermore, the bandwidth which can be covered by thenanocomposite with 4 and 8 vol.% of MWCNTs are about 4.3 GHz and 5.5 GHz, respectively. In fact, the presence of MWCNTs may cause extra dissipation because of the polarization and relaxation processes [23,26]. Furthermore, by increasing the concentration of MWCNTs, when electromagnetic waves travel inside the material, there would be more additional interfaces leading to multiple scattering [27]. This effect is favorable to widening absorption bandwidth [27,28].Fig. 6(d) shows that with a further increase ofMWCNTs content to 12 vol. %, the absorption bandwidth and maximum reflectionloss decrease. This might be related to the aggregation of MWCNTs in higher thana special content or high electrical conductivity at high MWCNTsloading [23, 28].As a result, most of the electromagnetic waves are reflected on the surfaceof the absorber layer [28,29]. Based on the findings of the present study, it can beconcluded that the presence of an optimum percentage of MWCNTs is a vitalfactor to achieve the best microwave absorption performance.It can be inferred from the RL curves that the nanocomposite with 8 vol. % of MWCNTs exhibits the bestabsorbing performance as compared to the other samples.
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4. Conclusion In summary, BaMg0.5Co0.5TiFe10O19nanoparticles were prepared by acoprecipitationmethod, and successfully attached along the side wall of thefunctionalized multi-walled carbon nanotubes. As presented in VSM graphs, itcould be found that by adding MWCNTs into the composite, the saturationmagnetization decreases as well as the coercivity.In the reflectivity curves also, itis well indicated that the microwave absorptionperformance of nanocomposites can be optimized by adding a certain amount ofMWCNTs. Consequently, the nanocomposite with 8 vol. % of MWCNTs and athickness of 2mm, could be proposed as a potential microwave absorber materialwith many applications in the Ku-band. Here, the bandwidth which could becovered by this sample is about 5.5 GHz.Generally, the excellent electromagneticwave absorption of the nanocomposite is resulted from the efficient complementbetween the permittivity and permeability of materials. This characteristic leads toa better matching of the dielectric and magnetic losses. Either only the magnetic orelectric loss may induce a weak electromagnetic wave absorption property due tothe imbalance of the electromagnetic match.
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References [1] A. N. Yusoff, M. H. Abdullah, S. H. Ahmed, S. F. Jusoh, A. A. Mansor, S. A.A. Hamid, Electromagnetic and absorption properties of some microwaveabsorbers, J. Appl. Phys. 92 (2002) 876-882. [2] D. D. L. Chung, Electromagnetic interference shielding effectiveness of carbonmaterial, Carbon. 39 (2001) 297-285. [3] L. Wang, H. Yu, X. Ren, G. Xu, Magnetic and microwave absorptionproperties of BaMnxCo1−xTiFe10O19, J. Alloys Compd. 588 (2014) 212-216. [4] C. Dong, X. Wang, P. Zhou, T. Liu, J. Xie, L. Deng, Microwave magnetic and absorption properties of M-type ferrite Ba(TiCo)xFe12-2xO19in the Ka band, J.Magn. Magn.Mater. 354(2014) 340-344. [5] S. Ozah, N. S. Bhattacharya, Nanosized barium hexaferrite in novolancphenolic resin as microwave absorber for X-band application, J. Magn. Magn.Mater, 342(2013) 92-99. [6] T. Inui, K. Konishi, K. Oda, Fabrication of broad-band RF-absorber composedof planar hexagonal ferrites, IEEE Trans. Magn. 35(1999) 3148-3150. [7] Z. W. Li, Z. H. Yang, L. B. Kong, Y. J. Zhang, High-frequency magneticproperties at K and Ka bands for barium-ferrite/silicone composites, J. Magn.Magn.Mater. 325 (2013) 82-86. 17
[8] Y. B. Feng, T. Qiu, C. Y. Shen, Absorbing property and structural design of microwave absorber based on carbonyl iron and barium ferrite, J. Magn. Magn.Mater. 318 (2007) 8-13. [9] P. Saini, V. Choudhary, B. P. Singh, R. B. Mathur, S. K. Dhawan, Enhancedmicrowave absorption behavior of polyaniline-CNT/polystyrene blend in 12.4-18GHz range, Synth. Metals. 161(2011) 1522-1526. [10] L. Li, K. Chen, H. Liu, G. Tong, H. Qian, B. Hao, Attractivemicrowaveabsorbingproperties of M-BaFe12O19ferrite, J. Alloys Compd. 557 (2013) 11-17. [11] C. L. Yuan, Y. S. Tuo, Microwave adsorption of Sr(MnTi)xFe122xO19 particles,J.
Magn. Magn.Mater. 342 (2013) 47-53.
[12] M. K. Tehrani, A. Ghasemi, M. Moradi, R. Shams Alam, Widebandelectromagnetic wave absorber using doped barium hexaferrite in Kuband, J.Alloys compd. 509 (2011) 8398-8400. [13] R. Shams Alam, M. K. Tehrani, M. Moradi, E. Hosseinpour, A. Sharbati, Therole of matching thickness on the wide band electromagnetic wave suppresserusing single layer doped barium ferrite, J. Magn. Magn.Mater.323(2011) 1040–1043. [14] R. Shams Alam, M. Moradi, M. Rostami, H. Nikmanesh, R. Moayedi, Y. Bai,Structural, magnetic and microwave absorption properties of doped Ba18
hexaferritenanoparticles synthesized by co-precipitation method, J. Magn. Magn.Mater. 381(2015) 1-9. [15] Y. Li, Y. Huang, S. Qi, L. Niu, Y. Zhang, Y. Wu, Preparation, magnetic andelectromagnetic properties of polyaniline/strontium ferrite/multiwalled carbonnanotubes composite, Appl. Surf. Sci. 258 (2012) 3659-3666. [16] W. Wang, Q. Li, C. Chang, Effect of MWCNTs content on the magnetic andwave absorbing properties of ferrite-MWCNTs composites, Synth. Metals161(2011) 44-50. [17] G. R. Gordani, A. Ghasemi, A. Saidi, Optimization of carbon nanotubesvolume percentage for enhancement of high frequency magnetic properties ofSrFe8MgCoTi2O19/MWCNTs, J. Magn. Magn.Mater. 363 (2014) 4954. [18] M. Asghari, A. Ghasemi, E. Paimozd, A. Morisako, Evaluation of microwaveand magnetic properties of substituted SrFe12O19 and substituted SrFe12O19/multiwalledcarbon nanotubes nanocomposites, Mater.Chem. Phys. 143 (2013)161-166. [19] D. Shi, J. P. Cheng, F. Liu, X. B. Zhang, Controlling the size and size distribution of magnetite nanoparticles on carbon nanotubes, J. Alloys Compd. 502 (2010) 365-370. [20] Q. Zhang, M. Zhu, Q. H. Zhang, Y. Li, H. Wang, The formation of magnetite 19
nanoparticles on the sidewalls of multi-walled carbon nanotubes, Compos. Sci.Technol. 69 (2009) 633-638. [21] G. Liu, L. Wang, G. Chen, S. Hua, C. Ge, H. Zhang, R. Wu, Enhancedelectromagnetic absorption properties of carbon nanotubes and zinc oxide whiskermicrowave absorber, J. Alloys Compd. 514 (2012) 183-188. [22] S. L. Shi, J. Liang, The effect of multi-walled carbon nanotubes onelectromagnetic interference shielding of ceramic composites, Nano. Technol. 19 (2008) 25507. [23] F. Qin, C. Brosseau, A review and analysis of microwave absorption inpolymer composites filled with carbonaceous particles, J. Appl. Phys. 111 (2012) 06131. [24] X. Tang, Y. Yang, K. Hu, Structure and electromagnetic behavior ofBaFe12_2x(Ni0.8Ti0.7)xO19-0.8xin the2-12GHz frequency range, J. Alloy Compd. 477(2009) 488-492. [25] S. M. Abbas, A.K. Dixit, R. Chatterjee, T. C. Goel, Complex permittivity,complex permeability and microwave absorption properties of ferritepolymerComposites , J. Magn. Magn.Mater. 309 (2007) 20-24.
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[26] T. Zhang, D. Huang, Y. Yang, F. Kang, J. Gu, Fe3O4/carbon compositenanofiber absorber with enhanced microwave absorption performance, Mater. Sci.Eng B. 178 (2013) 1-9. [27] A. Ghasemi, S. Javadpour, X. Liu, A. Morisako, Magnetic and reflection losscharacteristics of substituted barium ferrite/functionalized multiwalled carbonnanotube, IEEE. Trans. Magn. 47 (2011) 4310-4313. [28] A. Ghasemi, S. E. Shirsath, X. Liu, A. Morisako, A comparison betweenmagnetic and reflection loss characteristics of substituted strontium ferrite andnanocomposites of ferrite/carbon nanotubes, J. App. Phys. 111 (2012) 07B543.[29] Y. Zhai, Y. Zhang, Y. Ren, Electromagnetic characteristic and microwaveabsorbing performance of different carbon-based hydrogenatedacrylonitrilebutadiene,Mater. Chem. Phys. 133 (2012) 176-181.
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Figure captions Fig. 1. The XRD patterns of (a) functionalized MWCNTs, (b) doped barium hexaferrite nanoparticles, c) nanocomposite with 4 vol. % of MWCNTs, d) nanocomposite with 8 vol. % of MWCNTs, and (e) nanocomposite with 12 vol. % of MWCNTs. Fig.2.FTIR spectrum of (a) functionalized MWCNTs, (b) doped barium hexaferrite sample, and (c) nanocomposite with 8 vol. % of MWCNTs.
Fig. 3.SEM images of (a) pristine MWCNTs, (b) doped barium hexaferrite nanoparticles, (c) nanocomposite with 4 vol. % of MWCNTs, (d) nanocomposite with 8 vol. % of MWCNTs, and (e) nanocomposite with 12 vol. % of MWCNTs.
Fig.4. Hysteresis loops of (a) doped barium hexaferrite nanoparticles, and nanocomposites with (b) 4 vol. % of MWCNTs, (c) 8 vol. % of MWCNTs, (e) 12 vol. % of MWCNTs. Fig. 5.(a) The real ( 1 ) and imaginary part ( 1 ) of complex permittivity of doped barium hexaferrite sample and that of nanocomposite ( 2 , 2 ) with 8 vol. % of MWCNTs, and (b) The values of electric loss tangent of doped barium hexaferrite sample and nanocomposite with 8 vol. % of MWCNTs. Fig. 6. Reflection loss of (a) doped barium hexaferrite sample and nanocomposites with (b) 4 vol. % of MWCNTs, (c) 8 vol. % of MWCNTs, and (d) 12 vol. % of MWCNTs.
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Fig.1
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