Synthesis and physicochemical properties of

Synthesis and physicochemical properties of composites for electromagnetic shielding applications: a polymeric matrix impregnated with iron- or cobaltcontaining nanoparticles Gleb Yurjevich Yurkov Alexander Sergeevich Fionov Aleksander Vladimirovich Kozinkin Yury Alekseevich Koksharov Yevgeniy Anatolievich Ovtchenkov Denis Alexandrovich Pankratov Oleg Vladimirovich Popkov Valery Grigorievich Vlasenko Yuriy Aleksandrovich Kozinkin Marina Igorevna Biryukova Vladimir Vladimirovich Kolesov

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Synthesis and physicochemical properties of composites for electromagnetic shielding applications: a polymeric matrix impregnated with iron- or cobalt-containing nanoparticles Gleb Yurjevich Yurkov,a,f Alexander Sergeevich Fionov,b Aleksander Vladimirovich Kozinkin,c Yury Alekseevich Koksharov,d Yevgeniy Anatolievich Ovtchenkov,d Denis Alexandrovich Pankratov,d Oleg Vladimirovich Popkov,a Valery Grigorievich Vlasenko,c Yuriy Aleksandrovich Kozinkin,c Marina Igorevna Biryukova,a Vladimir Vladimirovich Kolesov,b Stanislav Vladimirovich Kondrashov,f Nikolai Alexandrovich Taratanov,e and Viacheslav Mikhailovich Bouznika,f a

Russian Academy of Science, A.A. Baikov Institute of Metallurgy and Materials Sciences, Leninsky pr. 49, Moscow 119991, Russia [email protected] b Russian Academy of Science, V.A. Kotelnikov Institute of Radio Engineering and Electronics, Mokhovaya st. 11-7, Moscow 125009, Russia c The South Federal University, Research Institute of Physics, pr. Stachki 194, Rostov-on-Don, 344104, Russia d M.V. Lomonosov Moscow State University, Vorobievy gory 1, Moscow 119991, Russia e Ivanovo Institute of State Fire Service of Emercom of Russia, pr. Stroiteley 33, Ivanovo, 153040, Russia f All-Russian Scientific Research Institute of Aviation Materials, Radio str. 17, 105005, Russia

Abstract. Magnetic, magnetic resonance, and structural properties of iron and cobalt nanoparticles embedded in a polyethylene matrix were studied. The materials were prepared by thermal decomposition of cobalt or iron formate in a polyethylene melt in mineral oil and contained from 2 to 40% wt. of metal. Transmission electron microscopy data indicate that the average diameter of particles is up to 8.0 nm. According to extended x-ray absorption fine structure and Mössbauer spectroscopy studies, the particles comprise a metallic core and nonmetallic shell which is chemically bound to the surrounding matrix. Electrophysical and magnetic properties of the materials prepared were studied along with their reflection and attenuation factors in the super high frequency band. The materials were found to be suitable for use in electromagnetic shielding. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JNP.6.061717]

Keywords: nanoparticles; nanocomposite; magnetization; magnetic resonance; magnetic anisotropy; radio absorption; electromagnetic shielding. Paper 12084SSP received Jun. 30, 2012; revised manuscript received Oct. 23, 2012; accepted for publication Oct. 23, 2012; published online Dec. 5, 2012.

1 Introduction The possibility of combination of properties specific for metals and polymers in a single material, as well as control of these properties by means of concentration variations, has been studied for a while.1,2 Different polymers can be used as the matrix in such a material, e.g., polyethylene,3–6 polypropylene,7 polytetrafluoroethylene,8 and others.9,10 These polymers exert relatively high thermal resistance, unique rheological properties and high dielectric strength and they are chemically inert and easily processable, which allows one to form items of any desired shape and size from them. It is also important that these polymers are produced using well-studied methods. 0091-3286/2012/$25.00 © 2012 SPIE

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Yurkov et al.: Synthesis and physicochemical properties of composites for electromagnetic . . .

Impregnation of polymer matrices with metal-containing nanoparticles allows creation of materials with interesting magnetic,11 electrophysical, and performance properties.12,13 A major advantage of composite materials, including nanocomposites, is the possibility of combination of conductivity, dielectric and magnetic properties in a single material, i.e., such materials combine properties of both the filler and the matrix.4,5,7–9,12–18 Besides that, it is possible to control magnetic and electrophysical properties of a nanocomposite by varying composition, size and concentration of the embedded nanoparticles. In particular, impregnation of dielectric polymers with carbon nanotubes,19–21 metal-containing fillers,16,22–25 results in formation of composites with enhanced conductivity compared to the pristine polymer matrix. The listed sources indicate that electric properties of composites depend on composition, shape, size, and concentration of the filler.26 The goal of this work was creation of new composite materials composed of the low-density polyethylene (LDPE) matrix impregnated with iron- or cobalt-containing nanoparticles. Composition, electrophysical and magnetic properties of the materials prepared were studied. Such new nanocomposites could be used in electromagnetic shielding applications.

2 Experimental Part 2.1 Preparation of Samples Materials comprised of iron- or cobalt-containing nanoparticles embedded in polyethylene matrix were prepared by means of thermal decomposition (thermolysis) of cobalt and iron formates in the polyethylene melt in mineral oil following the protocol described elsewhere.7,12 Synthesis was performed in argon flow at 290°C to 300°C. The argon flow rate was sufficient to provide rapid removal of ligands and solvent from the reactor vessel. A necessary amount of formate was added to the reaction mixture under vigorous stirring. Upon cooling down to room temperature, the obtained product was extracted from the reaction vessel and rinsed with benzene in order to get rid of the oil. Then the product was dried in vacuum and stored in air for further studies. The composite produced was a dark gray powder.

2.2 Transmission Electron Microscopy 2.2.1 Cobalt-containing nanocomposite Transmission electron microscopy (TEM) was used to confirm the presence of nanoparticles in the material and determine their dimensions. The studies were carried out using a JEOL JEM1011 electron microscope operating at 100 kV. The powder-like sample was dispersed by ultrasound in ethyl alcohol. Then the suspension was placed on carbon grid and dried. The resultant ultrafine polymeric powder was imaged. Figure 1(a) and 1(b) contains a TEM micrograph of the sample and histogram of the particles size distribution calculated based on the micrograph. The micrograph contains dark inclusions on the light background (polymeric matrix) attributed to the nanoparticles. According to the TEM data, the average diameter of the particles in the sample is 4.9 nm. Figure 1(c) is an HRTEM image of separate nanoparticles; this image displays the presence of a shell on the surface of the nanoparticles and energy-dispersive x-ray spectroscopy (EDS) spectra of the particles [Fig. 1(d)].

2.2.2 Iron-containing nanocomposite Micrographs in Fig. 2 have a light background (polyethylene) with distinct dark rounded spots (nanoparticles). TEM micrographs reveal a relatively uniform distribution of nanoparticles throughout the matrix. According to TEM images, the thermal decomposition of iron formate results in formation of spherical nanoparticles with the average size of 3.4 to 5.5 nm and size dispersion of 0.6 to 1.1 nm. Aggregation of nanoparticles during heating and compaction of the powder containing CFe ¼ 30% wt: results in an increase of their average diameter to 8 nm and their size dispersion to 2 nm. Journal of Nanophotonics

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Fig. 1 TEM (a), histogram of the particles size distribution (b), HRTEM (c) micrograph and EDS spectra (d) of the cobalt-containing nanocomposite.

2.3 EXAFS Studies Composition, electronic and atomic structure of the cobalt nanoparticles prepared was studied using extended x-ray absorption fine structure (EXAFS) and x-ray emission spectroscopy. The Co K-edge EXAFS of Co nanoparticles stabilized in polymer matrix was measured in the transmission mode using a laboratory EXAFS spectrometer designed on the basis of an x-ray spectrometer DRON-3M. Quartz (1340) was used as the crystal-analyzer. UWXAFS software27 was used for background removal, EXAFS extraction, and normalization of the absorption edge. Fourier transform of the EXAFS-function was carried out over the k-range from 2.5 to 12.0 Å−1 . The structure of bulk metallic cobalt is hcp at room temperature and fcc at 700 K. Each of these structures (hcp and fcc) or their combination may be found in Co nanoparticles.11 As one can see from the comparison of the modulus of the Fourier transform (MFT) of the Co K-edge EXAFS for the Co sample and calculated one for metal hcp and fcc Co structures (Fig. 3), MFT of hcp Co differs from MFT of fcc Co insufficiently. It is impossible to determine which structure type of Co realizes in nanoparticles. The question about Co structure in nanosize state is not clear at present time. Based on the analysis of literature data and sample synthesis temperature, we assume that the hcp structure should be expected, as it is more stable than fcc at room temperature. Moreover, we used both hcp and fcc structures of Co nanoparticles in the simulation. As the analysis of MFT cannot provide exact information on the structure type, the final choice of structure was based on the simulation results (by comparison of the calculated EXAFS function and the experimental one). So, the analysis of Co sample EXAFS spectrum was carried out assuming the hcp Co structure. The EXAFS MFT (Fig. 3) provides information about the nearest neighbor environment of Co atoms in nanoparticles. The MFT of the normalized EXAFS curve passes through maxima at rj ¼ Rj − αj , where Rj is the distance from the absorbing atom to the atoms of the j’th Journal of Nanophotonics

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Fig. 2 TEM micrographs of the iron-containing samples: A-sample 2, B-sample 2-t, C-sample 3, D-sample 3-t, E-sample 4.

Fig. 3 Modules of Fourier Transforms (MFTs) of the EXAFS functions of the sample studied along with calculated EXAFS functions of the hcp and fcc forms of the metallic Co. Journal of Nanophotonics

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coordination sphere, and αj is the phase correction which can be determined from the EXAFS spectra of compounds with known structures or by calculation. Figure 3 shows that the MFT of Co-containing nanoparticles has all features proper for Co metal except the first peak at r ¼ 1.52 Å. This peak may correspond to the Co─O or Co─C coordination shell. According to elemental analysis data, the sample contains less than 0.1% wt. of oxygen. Investigation of CoKβ5 -specrum also indicates that the Co─O interactions are absent, so the first coordination sphere probably contains C atoms, i.e., the first peak is a result of Co─C interactions. X-ray emission spectra support this assumption (see below). However, the features typical of Co carbides are absent in the MFT. This means that cobalt carbides do not form within the particles, but only the surface Co atoms interact with carbon atoms. Comparison of amplitudes of Co─C (r ¼ 1.52 Å) and the first Co─Co (r ¼ 2.18 Å) peaks reveals the presence of a large amount of Co─C bonds. It is possible that the number of surface atoms in nanoparticles is comparable with the number of atoms within them, which complies with the average size of the nanoparticles measured by TEM and the estimated ratio of surface atoms. Therefore, the qualitative analysis of the MFT indicates that the nanoparticles contain metallic cobalt and their surface atoms interact with carbon atoms. Additional calculations were performed in order to refine the nanoparticle structure model. The fitting was carried out in r-space over the range from 1.8 to 2.8 Å. According to this data, the Co─Co interatomic distance R is equal to 2.561 0.015 Å, coordination number (N) is 4 and mean square deviation of the interatomic distance from its equilibrium value (σ 2 ) is equal to 0.012 0.005 Å2 . This set of parameters corresponds to the minimum deviation of the calculated EXAFS MFT-function from the experimentally acquired one (3%). As one can see, the Co─Co interatomic distance is close to that in the metallic Co, where R ¼ 2.50 Å. The decrease of the coordination number from 12 in metal to 4 in nanoparticles can result from a large amount of surface atoms (F ¼ 37%) and also can be due to formation of imperfect crystallographic structure, namely a lattice with vacancies. The assumption about the imperfect structure complies well with the obtained Co─Co interatomic distance, which is larger than that in the Co metal by 0.05 0.01 Å. In fact, if the formed structure has vacancies then it is less dense, which can lead to an increase of the average interatomic distance. In addition, in this case, the amplitude of the “metallic” peak decreases and, as a result, the “carbon” peak is more prominent. For surface Co atoms interacting with carbon atoms, it is difficult to obtain the structural parameters by the fitting procedure. A set of different values of the structural parameters, including N and σ 2 , was obtained by the fitting for the same deviation of the theoretical EXAFS MFT-function from the experimental one (R-factor). The best fitting was achieved for Co─C interatomic distance R ¼ 2.07 Å, the coordination number from 4 to 6 and σ 2 from 0.003 to 0.01 Å2 , respectively. Such a set of parameters corresponds to the R-factor value of 3%. The obtained Co─C interatomic distance is in a good agreement with that in organometallic compounds of cobalt. The coordination number is also typical for organometallic compounds. Therefore, the following model of Co-nanoparticles stabilized in polyethylene matrix can be suggested. Nanoparticles consist of a metallic core and surface layer. The metallic core has vacancies, i.e., it is a rarefied (friable) structure. The surface of the Co nanoparticles interacts with carbon atoms like in metalorganic compounds of cobalt. This surface layer protects the particles from penetration of other carbon atoms or oxygen atoms from air; as a result, the metallic core is preserved within the particles. EXAFS studies made after three and six months of the sample preparation confirm that the crystal structure of Co nanoparticles is stable and does not change with time. The data acquired based on the analysis of the Co K-edge EXAFS spectra of cobalt atoms in the nanoparticles are listed in Table 1.

2.4 X-Ray Emission Spectra Electronic structure of the cobalt nanoparticles and the nature of chemical bonds between the surface cobalt atoms and the matrix were studied using the X-ray emission spectrometry (CoKβ5 line; Fig. 4). Journal of Nanophotonics

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Table 1 Composition and structural properties of the first coordination spheres of cobalt atoms in the nanoparticles prepared and metallic cobalt foil (the reference sample). Coordination sphere

Coordination number N, atoms

Radius R (Å)

Debye-Waller factor, σ 2 (Å2 )

Fitting, r -factor

0.03

Co þ PE 1

4C

2.07 (0.01)

0.009 (0.004)

2

4 Co

2.561 (0.015)

0.012 (0.005)

Co foil 1

6 Co

2.4984

0.0065

6 Co

2.5102

0.0065

2

6 Co

3.5457

0.0108

3

2 Co

4.0714

0.0069

0.0075

Fig. 4 X-ray emission CoKβ5 spectra: (1) Co foil; (2) Co þ PE.

CoKβ5 spectra origin from transitions of valent p-electrons in cobalt to the 1s-vacancy and carry information about the distribution of cobalt valent p-electron states. Occupation of the 4p states which are vacant in the metallic cobalt can be regarded as a modification of wavefunction tails of adjacent atoms, the tails which spread into the core orbitals of an emitting atom and adopt the nodular shape of its valent p orbitals. This approach provides means for using the Kβ5 spectra for solving qualitative structural problems, as these spectra will reflect the appearance of the levels of ligand molecular orbitals (MO) or atomic orbitals (AO) of the atoms coordinated to an emitting cobalt atom. Figure 4 depicts CoKβ5 spectra of the Co/PE nanomaterial studied and cobalt foil; the main properties of these spectra are listed in Table 2. The figure also contains spectra corrected by the cobalt inner K level width using the iterative method based on the Bayes theorem. Table 2 Key properties of CoKβ5 spectra of the cobalt nanoparticles prepared and reference material (cobalt foil). E m is the energy of a spectral maximum, a 0 0 is the asymmetry index, γ is the full width of a signal at half maximum. Spectral component position E m (eV) A

B

C

a00

γ

Co

7705.9

—

—

1.52

6.8

Co þ PE

7705.9

7702.8

7696.8

1.57

12.2

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The spectra of the nanomaterial studied and cobalt foil differ significantly. The former has extra features which indicate that the nanoparticles contain cobalt compounds with the valent p-band different from the one specific for the metal. Position of the main maximum A in the spectrum of the sample studied coincides with that of the respective maximum of the foil spectrum; it corresponds to the interaction of valent p electrons of cobalt with 3d electrons of adjacent cobalt atoms (the metal-metal bond). It indicates that the majority of cobalt in the nanoparticles is in the metallic form (presumably, in the form of a metallic core). Besides the main maximum A, the CoKβ5 spectrum if the particles studied contains extra maxima B and C in the low energy zone; those components are absent in the spectrum of foil. Component B shifted by 3 eV from the main maximum A, based on its position, was attributed to the interaction of valent p electrons of cobalt with 2p electrons in carbon orbitals. This result is confirmed by the presence of the component C which is shifted by 6 eV from the component B and corresponds to the interaction of valent p electrons of cobalt with 2s electrons in carbon orbitals. Therefore, CoKβ5 x-ray emission spectra indicate that the nanoparticles in the Co/PE sample contain metallic cobalt and nonmetallic cobalt compounds. As it follows from the analysis of the spectra, there is a chemical interaction between the surface of the nanoparticles and the polyethylene matrix: there are chemical bonds between cobalt atoms in the nanoparticles and carbon atoms in the matrix. Figure 5 contains x-ray emission CoKβ1 β 0 spectra of the material studied; its key properties are listed in Table 3. The CoKβ1 β 0 spectra are comprised of high-intensity high energy Kβ1 maximum and low-energy Kβ 0 bump. They origin from the transitions of 3p electrons in cobalt (which do not contribute to a chemical bond) to the 1s vacancy, and the position of Kβ1 maximum and intensity of Kβ 0 bump can be used for estimation of the number of uncoupled 3d electrons (ne ), localized in a 3d metal atom. So, an increase of ne results in a higher intensity of the Kβ 0 bump and higher energy of the Kβ1 maximum in the CoKβ1 β 0 spectra. As depicted by Fig. 6, the CoKβ1 β 0 spectrum of the sample studied has a prominent β 0 component and the CoKβ1 maximum is shifted by 1 eV relative to the respective maximum of the foil spectrum; the latter maximum energy is close to that of the Co3 O4 spectrum maximum. Taking into account specifics of the CoKβ1 β 0 multiplet structure formation, the number of uncoupled 3d electrons was estimated by the method used for estimation of uncoupled 3d electrons in iron atoms, that is, if the center of gravity of a multiplet remains at the same energy as in case of metalic cobalt, the shift of the Kβ1 maximum can be used to perform an accurate estimation. As it follows from Table 3, energies of the centers of gravity of both the CoKβ1 β 0 spectra lie within 0.2 eV from each other, whereas the maxima are 1.1 eV apart. For the reference cobalt compounds (Co foil, CoO, Co3 O4 ) with known ne (see Table 3) we determined linear dependences of the CoKβ1 maximum energy shift as a function of ne for the constant position of the center of gravity of the spectra (Fig. 5). Knowing this dependence and

Fig. 5 The x-ray emission CoKβ1 β 0 spectra: (1) Co foil; (2) Co þ PE. Journal of Nanophotonics

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Fig. 6 Dependence of the energy shift of the CoKβ1 - maximum as a function of ne for reference compounds: 1─Co foil; 2─Co3 O4 ; 3─CoO. The arrow points to the ne value in the cobalt nanoparticles studied.

the energy of the CoKβ1 maximum for the nanomaterial studied, we revealed that cobalt atoms in the nanoparticles are in a high-spin state with the number of uncoupled 3d electrons per atom equal to ne ¼ 3.1. Therefore, the results of x-ray emission and EXAFS spectroscopy studies of the Co þ PE material allow us to propose the following structural model of cobalt nanoparticles in it. A nanoparticle contains a metallic core with structural defects (cobalt vacancies). The surface atoms of a nanoparticle interact with carbon atoms in the polyethylene matrix with formation of a carbide layer, which prevents other carbon and oxygen atoms from accessing the core of a particle, so the core remains metallic over time. The latter was confirmed using nuclear magnetic resonance.28

2.5 XRD and Mössbauer Spectroscopy X-ray diffraction (XRD) patterns of the powdered and pelleted samples were recorded using a DRON-3M diffractometer (CuKα radiation, λ ¼ 0.154056 nm, pyrographite monochromator, scanning rate: 2°∕ min). The PDF2 database published by the JCPDS (2004) was used for reference. The cobalt-containing composites were found to be amorphous, and their composition could not be determined based on the XRD patterns. Patterns of the high-concentration (30, 40% wt.) Fe/PE samples lack peaks specific for Fe2 O3 (JCPDS 15-0615) found in the patterns of the samples with lower concentration of iron. Also, the peak intensity lowers with the rise of iron concentration. It indicates that pelletings induced reduction of Fe2 O3 and Fe3 O4 in the high-concentration composites. Table 3 Key properties of the CoKβ1 β 0 spectra of the nanoparticles studied and reference materials. E m and E u;m are energies of maxima and centers of gravity of the spectra, ΔE is the shift of spectral maxima relative to E m in the metallic cobalt, “a” is the asymmetry index, γ is the peak full width at half maximum, ne is the number of uncoupled 3d electrons in a cobalt atom. E m (eV)

E u;m (eV)

ΔE (eV)

a

γ

ne

Co

7649.4

7647.8

0.0

1.1

5.6

1.72

Co3 O4

7650.6

7647.9

1.2

1.4

6.4

3.25

CoO

7650.8

7648.0

1.4

1.6

6.5

3.52

Co þ PE

7650.5

7648.0

1.1

1.4

7.2

3.10

Sample


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Mössbauer absorption spectra were recorded at room temperature using an express Mössbauer spectrometer MS1101. The γ radiation was emitted by a standard enclosed source containing 57 Co in metallic rhodium (1 to 5 mCi) by ZAO “Tsiklotron.” The isomer shifts are given relative to α-Fe. The spectra were processed using “UNIVEM v.4.50” software. According to Mössbauer spectroscopy, the samples prepared from iron formate mainly contain magnetically ordered phases (Fig. 7 and Table 4). The largest area signals in the spectra [Fig. 7(a), subspectra 1-3] correspond to the mixed iron (II, III) oxide which has the spinellike29 structure (Fe3 O4 ). Subspectra 1 and 2 correspond to the iron atoms that form the core of nanoparticles crystallites, whereas subspectrum 3 corresponds to the atoms located on the particle surface and has the relaxation origin. The somewhat undersized value of the chemical shift of the sample’s 1 subspectrum 2 (iron atoms in tetrahedral interstices) indicates that the Fe3 O4 is highly defective. This is obviously caused by a higher concentration of the iron (III) ions in the said interstices compared to those of the sample 3, which results in the lower chemical shift. The presence of the oxidizing atmosphere during the synthesis of the sample 1 [Fig 7(a)] affected its spectrum in the way that it contains a doublet corresponding to iron (III) atoms (subspectrum 4). This subspectrum corresponds to superparamagnetic Fe2 O3 which can comprise whole nanoparticles or form the surface layer of Fe3 O4 nanoparticles. The latter assumptions are more expectable because the particle size distributions determined based on TEM images have a single mode. Synthesis of sample 3 [Fig 7(a)] with higher CFe (compared to sample 1) was carried out in a reductive atmosphere, which prevented formation of oxides. It is evidenced by the presence

Fig. 7 Mössbauer spectra of the iron-containing samples: (a) sample 1; (b) sample 3; (c) sample 4; (d) sample 4 after annealed in argon; and (e) sample 4 after annealed in air. Journal of Nanophotonics

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Table 4 Parameters of Mössbauer spectra of the iron containing samples.

Sample 1

3

4 (initial)

4 (annealed in argon)

4 (annealed in air)

C Fe (% wt.)

Subspectrum

δðmm∕sÞ

Δðmm∕sÞ

B hf (kOe)

Γexp ðmm∕sÞ

S rel (%)

10

1

0.30 0.01

0.01 0.01

488.3 0.3

0.44 0.01

33

2

0.59 0.01

0.03 0.01

455.0 0.6

0.62 0.03

32

3

0.65 0.04

0.06 0.06

411.9 0.6

1.32 0.12

18

4

0.35 0.01

0.71 0.01

–

0.52 0.01

18

1

0.32 0.01 −0.02 0.01

489.7 0.1

0.44 0.01

48

2

0.67 0.01

−0.02 0.01

456.5 0.1

0.38 0.01

32

3

0.53 0.02 −0.08 0.04

418.8 2.0

0.82 0.10

8

4

0.00 0.01 −0.01 0.01

330.4 0.4

0.26 0.02

4

5

0.26 0.05 −0.04 0.04

202.0 1.7

0.83 0.07

8

1

0.28 0.01

0.01 0.01

492.2 0.1

0.38 0.01

39

2

0.64 0.02

0.04 0.01

458.5 0.1

0.52 0.01

45

3

−0.01 0.01

0.00 0.01

330.1 0.2

0.27 0.01

11

4

0.67 0.01

2.27 0.01

—

0.19 0.02

2

5

0.63 0.05

—

—

1.34 0.24

3

1

0.28 0.01

0.02 0.01

490.1 0.1

0.31 0.01

34

2

0.64 0.02

0.03 0.01

457.7 0.1

0.50 0.01

60

3

−0.01 0.01

0.02 0.01

329.9 0.3

0.20 0.02

4

4

0.65 0.01

2.30 0.01

—

0.23 0.02

2

1

0.28 0.01

0.01 0.01

492.2 0.1

0.29 0.06

4

2

0.64 0.02

0.04 0.01

458.5 0.1

0.78 0.05

6

3

0.32 0.02

0.03 0.01

503.4 0.2

3.69 0.59

87

4

0.33 0.01

2.46 0.2

—

0.27 0.03

3

30

40

40

40

δ is the isomer chemical shift, Δ is the quadrupole splitting, B hf is the effective magnetic field, Γexp is the experimentally measured linewidth линии, S rel is the relative peak area.

of lines corresponding to the magnetically ordered θ-modification of iron carbide Fe3 C (subspectrum 5)30 and metallic α-Fe (subspectrum 4).31 The considerable linewidth testifies to high defectiveness of the carbide phase and, probably, small size of the respective particles. Sample 4 [Fig. 7(c)] contains Fe3 O4 (subspectra 1 and 2), ca. 11% α-Fe (subspectrum 3), and nanoscale (superparamagnetic) Fe3 O4 (subspectrum 5). Sample 4 was also annealed in argon [Fig. 7(d)] or air [Fig. 7(e)]. Annealing in argon resulted in enlargement of superparamagnetic particles and oxidation of the metallic iron (its concentration is only 4%). Concentration of Fe3 O4 in the sample annealed in air (subspectra 1 and 2) is considerably lower than in the sample annealed in argon, and most of iron is in the form of γ-Fe2 O3 (subspectrum 3). The presence of doublets 1–4, 2–4, and 4–4 can be explained by manifestation of the samples’ texture.

2.6 Magnetic and Magnetic Resonance Properties We have measured temperature and field dependencies of magnetization with the help of the vibrating sample magnetometer (model PARC-155, Princeton Applied Research) with a flow Journal of Nanophotonics

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helium cryostat and a home-made high temperature insert. The magnetometer sensitivity is better than 5 × 10−5 emu. The magnetic measurements were carried out in the temperature range from 4.2 to 380 K and in magnetic fields of up to 4.5 kOe. Measurements of hysteresis loops were made by the first saturating of the sample in the field of 4.5 kOe. EMR studies were carried out using X-band (∼9.2 GHz) spectrometer Varian E-4. The temperature was controlled by the nitrogen temperature system E-257 (Varian) from 295 to 495 K and platinum thermoresistor with accuracy of 1 K. The width of resonance spectra lines was determined by the “peak-topeak” method. The registration and analysis of a microwave absorption field hysteresis in low magnetic fields were conducted according to a procedure described in Ref. 32. Figure 8(a) presents the hysteresis loops of the sample containing Co in polyethylene matrix measured at 4.2, 77, and 295 K. The rather high coercive force (590 Oe) observed even at room temperature witnesses that the system of nanosize magnetic particles in the sample is in the blocked state. The coercive force increases under cooling and reaches 680 Oe at 4.2 K. The magnetization value in the strongest magnetic field used (H max ≈ 4.5 kOe) also increases under cooling. The magnetization field behavior changes qualitatively: the room temperature magnetization at H max approaches the saturation value, while there is no saturation at 4.2 K and only the minor hysteresis loop is observed. Such behavior can be related with the magnetic anisotropy rising in the low temperature region. The high magnetization value—1.05 μB ∕atom at 295 K and 1.95 μB ∕atom at 4.5 K in the field of 4.5 kOe attracts attention. According to Ref. 33, the saturation magnetization in bulk Co is 1.7 μB ∕atom, i.e., in our samples we have higher saturation magnetization values per Co atom than in a bulk state. According to the Stoner-Wohlfarth model, the coercive force temperature dependence for a system of superparamagnetic particles in the blocked state can be described by the following equation:34,35 H c ðTÞ ¼ H c ð0Þð1 − aT β Þ;

(1)

where H c ð0Þ is the coercive force value at T ¼ 0 K, a is a coefficient and the exponent β is equal to 1∕2. However, in the investigated sample with 4% wt. of Co in polyethylene matrix, the dependence (1) with β ¼ 1∕2 did not obey the experimental data. The best fit was achieved for β ¼ 2. Figure 8(b) shows experimental points and the simulation curve H c ðTÞ with β ¼ 2 for the temperature dependence of the coercive force in the sample under investigation. The extrapolation to the high temperature region shows that the coercive force should become equal to zero at 560 K. This temperature can be regarded as the blocking temperature T b of the sample. Typical magnetic resonance spectra of the cobalt-containing nanocomposites are shown in Fig. 9(a). First of all, it should be noted that the resonance lines have rather large width. At the maximum temperature of our experiments (∼500 K), the line width ΔHpp was about 2500 Oe. Cooling down to room temperature leads to the increase of ΔH pp up to 3000 Oe. At all temperatures the resonance line is significantly shifted from the field, corresponding to the free spin

Fig. 8 The hysteresis loops (a) of the sample containing Co in polyethylene matrix measured at 4.2 (curve 1), 77 (curve 2) and 295 K (curve 3) and temperature dependence of the coercive force (b). Journal of Nanophotonics

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Fig. 9 Typical magnetic resonance spectra of the cobalt-containing nanocomposites at 297 K and 490 K (a); hysteresis of the microwave absorption signal in low fields (b).

spectroscopic factor g ¼ 2, to the low fields [Fig. 9(a)]. At the high temperatures it is possible to discern the second narrower and weaker line near g ¼ 2. The second feature of the investigated magnetic resonance spectra is a pronounced hysteresis of the microwave absorption signal in low fields [see Fig. 8(b)]. The temperature dependence of the phenomenological parameter ΔZeff (in per-unit), which is proportional to a remanent magnetization,33 is presented in Fig. 9. The dependence ΔZeff ðTÞ can be with enough accuracy approximated by a linear dependence A þ BT, where A ¼ 17.0 0.5 and B ¼ ∼ð0.024 0.001Þ K−1 . The parameter ΔZeff becomes zero at T ¼ −A∕B ≈ 700 K. Because many magnetic characteristics (for example, the saturation magnetization, the susceptibility) obey an exponential law under approaching to the temperature of the phase transition from the magnetically ordered to the disordered state, we fitted experimental ΔZeff ðTÞ dependence by the exponential function ðT 0 − TÞ0 (see Fig. 9). The fitting parameters were found to be T 0 ¼ ð630 140Þ K and α ¼ 0.7 0.4. So, according to the magnetic resonance data, the remnant magnetization becomes zero at the temperature about 600 K, in good accordance with the magnetization data. The investigated samples were also subjected to a heat treatment in air under the temperature of 280°C for 2 h. The results of magnetic measurements at room temperature on the asprepared and heat-treated samples are presented in Table 5. As one can see, the heat treatment does not lead to the change of the coercive force value, but to the about twice increase of the sample magnetization. This magnetization changing can be connected with the crystal structure transformation of the particles during heat treatment. The magnetic resonance spectra of the studied Co nanoparticles obey general regularities typical of ferromagnetic nanoparticles: the resonance line narrows with temperature increasing and at high temperatures the second narrow line becomes noticeable in the spectrum. The unusual feature of the studied Co nanoparticles (for example, in comparison with Fe nanoparticles) is the broad width of the resonance line (above 2 kOe for all temperatures). To estimate the anisotropy energy from the magnetic resonance data we used the results of de Biasi et al.36 For singledomain randomly oriented spherical nanoparticles the width of a magnetic resonance line cannot be smaller than the anisotropy field H a with correction to superparamagnetic fluctuations. The anisotropic field for fcc Co H a ¼ K∕I s ≈ 1.6 kOe. After taking into account the thermal fluctuations (for the particles with the diameter of 4.9 nm) this value decreases to about 400 Oe. Journal of Nanophotonics

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Table 5 Coercive force H c , remanent magnetization M r , magnetization in the field of 4.5 kOe at room temperature for the as-prepared and heat-treated at 280°C for 2 h cobalt-containing samples. H c (Oe)

M r (μB )

M H¼4.5 (μB )

Initial

590

0.35

1.05

heat-treated

590

0.62

1.96

Because in our case the resonance line width at 295 K is ∼3 kOe, the anisotropy field (and, correspondingly, the anisotropy energy) is about 7 to 8 times larger than in the bulk cobalt. This does not contradict to the data obtained from the magnetization measurements. Data on coercive force H C and iron concentration CFe in iron-containing samples are listed in Table 6. Values M s are given per sample mass unit (the Ms values in parantheses are per a mass unit of iron). Increase of CFe results in increase of Ms and H C . Increase of CFe from 30 to 40% wt. results in lower magnetic moment per particle, which can be explained by lower concentration of a magnetically ordered phase in the composite. EMR spectra of samples with different CFe values are depicted in Fig. 10(a). Table 7 contains main EMR signal parameters: linewidth ΔH pp determined by the “peak-to-peak” method and effective g-factor calculated by the formula gef ¼ 2.00H st ∕H res ;

(2)

where H res is the resonance field of an EMR signal determined by the “peak-to-peak” method, H st is the resonance field of the reference sample (DPPH) signal with gef ¼ 2.00. Linewidth increases (approximately by 1∕3) along with the increase of CFe from 20 to 30% wt. It is connected with diminished interparticle distance and more intense magnetic interactions between particles. However, the difference between EMR linewidths of samples with CFe equal to 30 and 40% wt. is within measurement error. Supposedly, a specific structure comprised of interacting particles forms in the region of concentrations CFe ≈ 20 : : : 30% wt. So, the futher increase of iron concentration does not alter the local magnetic surrounding of nanoparticles and, therefore, does not increase the EMR linewidth of the powdered sample.37 It is interesting that the EMR linewidth of the pelleted (compacted under pressure) sample is lower than that of the initial powdered sample [Fig. 10(a)]. Compaction, obviously, results in a more ordered packing of nanoparticles in the polymer matrix and, therefore, less spread of local magnetic field strength values affecting a particle. The average value of the effective local field rises which is indicated by the increase of the g-factor (see Table 7) in the sample 3-t after compaction. The EMR signal shape for the sample with the minimum CFe value is close to Gaussian [Fig. 10(b)]. It testifies to nonuniformity of the line broadening which is presumably connected with the dipole-dipole interaction between the nanoparticles. As the CFe value increases to 30% wt., the EMR line becomes asymmetric (Fig. 10), which may be caused by a change in the sample’s morphology (transition from separate particles to a connected structure) or increase of electrical conductivity of the samples with the exceedance of the percolation threshold.

Table 6 Parameters of demagnetization curves of the samples studied. C Fe , % wt.

M S , Gs · cm3 ∕g)

H C (Oe)

m 0 (μB )

2

20

16.3 (81,5)

104

10150

3

30

67.5 (225)

220

11450

4

40

89.7 (224)

280

8400

Sample


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Fig. 10 EMR spectra of the samples with different concentration of iron-containing nanoparticles (a); EMR spectrum of powder sample 2 (dots) and Gaussian approximation (solid line) (b).

2.7 Electrophysical Properties The specific volume resistance ρV and relative permittivity ε of the nanocomposites were determined based on data acquired using a two-electrode capacitance cell by placing a pelleted sample between its electrodes. Cell resistance was measured using voltmeters B7-40 (for low resistance) and B7E-42 (for high resistance); cell capacitance was measured using LCR meters E7-8 (at 1 kHz) and E7-12 (at 1 MHz).12 The feature specific for the nanocomposites based on iron-containing nanoparticles with their content not exceeding 20% wt. (samples 1-t, 2-t) is their high specific volume resistance ρV ≈ 1011 : : : 1012 Ωm comparable with ρV of the pristine polyethylene (sample 0-t, 1014 Ωm) which was subject to the full synthesis cycle without being impregnated with nanoparticles. Table 7 EMR linewidth and effective g-factor for the samples studied. Linewidth Δ H pp (Oe)

Effective g-factor

2

1725 5

2.44 0.01

2-t

1705 5

2.36 0.01

3

2220 10

2.42 0.02

3-t

1900 10

2.65 0.02

4

2210 10

2.47 0.02

Sample


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Specific volume resistance of the sample with CFe ¼ 30% wt: (sample 3-t) is 40 Ωm. Such ρV values are typical for pelleted materials, as well as materials with high hopping electron conductivity. This type of conductivity in a nanocomposite comprised of a polymer matrix impregnated with metal-containing nanoparticles has a threshold nature, which was noted during analysis of EPR spectra, and estimations of the threshold made in the range of CFe ≈ 20 : : : 30% wt: coincide. The hopping conductivity is favored by larger particles sizes, as they result in broader energy spectra of electrons and thinner dielectric layer between particles. The existence of the tunnel conductivity in composites comprised of a polymer matrix and metal-containing nanoparticles has been justified elsewhere.38 The existence of this type of conductivity in a material can be determined based on its current-voltage curve. If the tunnel conductivity takes place, for voltages above some threshold value, the curve is described by the equation:38 j ¼ AV n expð−B∕VÞ; (3) where j is the current density, V is the voltage, A, B, and n are constants. A current-voltage curve has been plotted for the sample 2-t in the voltage range of 100 : : : 1000 V in (V lnðj∕AÞ; V ln V) coordinates (Fig. 11). Its shape indicates that the tunnel mechanism takes place in the sample. The results of relative permittivity (ε) measurements on the nanocomposites prepared are listed in Table 8. The increase of ε after impregnation of the matrix with the filler is caused by the extra contribution from nanoparticle polarization.

2.8 Properties of the Samples in the SHF Radio Band The reflectance and attenuation coefficients of the materials were measured using the VSWR and attenuation meter (at 25 and 30 GHz) in a waveguide duct. The pelleted samples were formed into waveguide inserts with the size conforming to the waveguide cross-section. The inserts were put in the measurement cell (a waveguide segment with the conforming cross-section). Measurements were carried out for two sample positions relative to the oscillator, so that the

Fig. 11 I–V characteristic of sample 2-t.

Table 8 Relative permittivity (ε) of the samples. ε C Fe (% wt.)

f ¼ 1 kHz

f ¼ 1 MHz

0-t

0

2.30

2.25

2-t

20

4.95

3.30

Sample

Note: f is the operational frequency.


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electromagnetic wave was incident on the sample from both its sides. Calibration of the total reflection level was performed using a short located at the exit of the empty measurement cell. The attenuation coefficient A was calculated as the ratio of the power of the radio signal transmitted through the cell with a sample and the incident power: A ¼ −10 lg

Ptr ; ½dB. Pinc

(4)

The reflectance coefficient R was calculated as the ratio of the reflected radio power and the incident power: A ¼ −10 lg

Ptr ; ½dB. Pinc

(5)

The relative reflectance coefficient R was calculated based on the value R : R¼

Rloss : Pinc

(6)

The relative loss coefficient (L) was calculated based on known R and A: L¼

Ploss : Pinc

(7)

Table 9 lists values of reflectance and attenuation coefficients at 25 and 30 GHz measured on a sample placed in a waveguide of the conforming cross-section. The increase of the radiosorption in the samples along with the increase of CFe is caused by the decrease of specific volume resistance (losses due to conductivity and ring currents) and the presence of a magnetic phase (losses due to remagnetization). Table 10 contains data on permittivity of the materials at 1 kHz and 1 MHz. It is obvious that composite materials synthesized using the same technological approach (thermal decomposition of metal-containing compounds in a LDPE-oil solution-melt in this case) can have a wide range of electrophysical properties. This fact allows for the development and manufacture of materials with the desired properties by varying nanoparticle composition, their concentration in the polyethylene matrix, or using combinations of composites with different nanoparticles. Table 9 Attenuation (A), reflection (R) and loss (L) coefficients of the samples. R Sample

L

A (dB)

h (mm)

25 GHz

30 GHz

25 GHz

30 GHz

25 GHz

30 GHz

3-t

2.9

0.61

0.53

0.32

0.42

11.60

13.0

2-t

0.95

0.35

0.22

0.0

0.09

1.35

1.6

0-t

1.2

—

0.12

—

0.0

—

0.3

Table 10 Experimental values of permittivity at 1 kHz and 1 MHz, and attenuation and reflectance coefficients at 30 GHz for composite nanomaterials based on LDPE. Metal-containing component concentration (% wt.)

ε (1 kHz)

ε (1 MHz)

K refl (30 GHz)

K att , dB∕cm (30 GHz)

PE þ Co

4

3.96

3.01

0.03

30.1

PE þ Co

30

8.84

4.89

0.08

77.3

Sample composition


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3 Conclusions A technology for small-scale production of nanostructured materials based on cobalt- and iron-containing nanoparticles has been developed. Structural analysis results indicate that the nanoparticles have a complex structure: the cobalt-containing particles are composed of hcp metallic cobalt and cobalt carbide, whereas the iron-containing particles are composed of iron oxides. The investigations of the static magnetization and the microwave resonance absorption have showed that Co nanoparticles in a polyethylene matrix display a set of interesting properties. First of all, it is enhanced (in comparison with the bulk value) magnetic moment per atom. Secondly, it is the record blocking temperature, notably higher than the room temperature. The high blocking temperature points to high magnetic anisotropy, which can be apparently related with surface effects. Basic electrophysical properties of the materials prepared have been studied; the materials are efficient for use in electromagnetic shielding applications.

Acknowledgments A.S.F. acknowledges support from RFBR Grant No. 11-08-00015a. V.V.K. acknowledges support from RFBR Grant No. 12-07-00749a and 11-07-00278a. N.A.T. thanks the federal target program Scientists and Science Teachers of an Innovative Russia Grant No. 2012-1.2.1-12-0002013-7468. M.I.B. acknowledges support from RFBR Grant No. 12-03-33034mol-a-ved. V.M.B. is grateful for support from RFBR Grant No. 11-03-12068ofi-m-2011 and the Grant of President RF NSh-3550.2012.3. Dr. G.Yu. Yurkov, Dr. N.A. Taratanov and M.I. Biryukova are responsible for the synthesis of the iron containing sample. Dr. G.Yu. Yurkov, Dr. S.V. Kondrashov and O.V. Popkov are responsible for the synthesis of the cobalt containing sample. Dr. G.Yu. Yurkov performed TEM, HRTEM and SEM measurements. Dr. A.V. Kozinkin, Dr. V.G. Vlasenko, Dr. Yu. A.Kozinkin were responsible for the EXAFS and x-ray emission spectroscopy measurements and data analysis. Dr. D.A. Pankratov performed Mossbauer spectroscopy measurements and respective data analysis. Dr. A.S. Fionov and Dr. V.V. Kolesov were responsible for the electrophysical measurements and respective data analysis. Dr. Yu.A. Koksharov and Y.A. Ovtchenkov performed the ESR and magnetic measurements and respective data analysis. Dr. G.Yu. Yurkov and Academician V.M. Bouznik have supervised this research work. All the authors contributed to analysis of all the gathered data in order to link them together into a big picture and form conclusions based on them.

References 1. A. S. Edelstein and R. C. Cammarata, Nanomaterials: Synthesis, Properties and Applications, Institute of Physics Publishing, Bristol and Philadelphia (1998). 2. A. D. Pomogailo, A. S. Rozenberg, and I. E. Uflyand, Metal Nanoparticles in Polymers, Khimiya, Moscow (2000). 3. T. W. Smith and D. Wychick, “Colloidal iron dispersions prepared via the polymercatalyzed decomposition of iron pentacarbonyl,” J. Phys. Chem. 84(12), 1621–1629 (1980), http://dx.doi.org/10.1021/j100449a037. 4. N. A. Taratanov et al., “Creation and physical properties of the molybdenum-containing polyethylene-based nanomaterials,” J. Commun. Technol. Electron. 54(8), 937–946 (2009), http://dx.doi.org/10.1134/S1064226909080099. 5. J. I. Hong, L. S. Schadler, and R. W. Siegel, “Rescaled electrical properties of ZnO/low density polyethylene nanocomposites,” Appl. Phys. Lett. 82(12), 1956–1958 (2003), http://dx.doi.org/10.1063/1.1563306. 6. G. Yu. Yurkov et al., “Copper nanoparticles in a polyethylene matrix,” Inorg. Mater. 37(10), 997–1001 (2001). 7. S. P. Gubin, Y. G. Yurkov, and I. D. Kosobudsky, “Nanomaterials based on metal-containing nanoparticles in polyethylene and other carbon-chain polymers,” Int. J. Mater. Prod. Technol. 23(1–2), 2–25 (2005), http://dx.doi.org/10.1504/IJMPT.2005.006587. Journal of Nanophotonics

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8. G. Y. Yurkov et al., “New magnetic materials based on cobalt and iron-containing nanoparticles,” Compos. Part B-Eng. 37(6), 413–417 (2006), http://dx.doi.org/10.1016/j .compositesb.2006.02.007. 9. U. Abdurakhmanov et al., “Electric conductivity of composite materials based on phenylon matrices and nickel particles,” J. Commun. Technol. Electron. 55(2), 221–224, (2010), http://dx.doi.org/10.1134/S1064226910020154. 10. X. H. Li et al., “Fabrication and properties of poly(propylene carbonate)/calcium carbonate composites,” J. Polym. Sci. Part B-Polym. Phys. 41(15), 1806–1813 (2003), http://dx.doi .org/10.1002/(ISSN)1099-0488. 11. S. P. Gubin et al., “Magnetic nanoparticles: preparation, structure and properties,” Russ. Chem. Rev. 74(6), 489–520 (2005), http://dx.doi.org/10.1070/RC2005v074n06ABEH000897. 12. G. Y. Yurkov et al., “Electrical and magnetic properties of nanomaterials containing iron or cobalt nanoparticles,” Inorg. Mater. 43(8), 834–844 (2007), http://dx.doi.org/10.1134/ S0020168507080055. 13. A. S. Fionov et al., “Absorbers of electromagnetic waves on the based iron and cobalt nanoparticles,” Perspektivnye Materialy 6(1), 192–196 (2008) (in Russian). 14. M. Zanetti, S. Lomakin, and G. Camino, “Polymer layered silicate nanocomposites,” Macromol. Mater. Eng. 279(1), 1–9 (2000), http://dx.doi.org/10.1002/1439-2054 (20000601)279:13.0.CO;2-Q. 15. X. Xia, S. Cai, and C. Xie, “Preparation, structure, and thermal stability of Cu/LDPE nanocomposites,” Mater. Chem. Phys. 95(1), 122–129 (2006), http://dx.doi.org/10.1016/j .matchemphys.2005.05.010. 16. J. I. Hong, L. S. Schadler, and R. W. Siegel, “Rescaled electrical properties of ZnO/low density polyethylene nanocomposites,” Appl. Phys. Lett. 82(12), 1956–1958 (2003), http://dx.doi.org/10.1063/1.1563306. 17. S. C. Tjong and Y. Z. Meng, “Structural-mechanical relationship of epoxy compatibilized polyamide 6/polycarbonate blends,” Mater. Res. Bull. 39(11), 1791–1801 (2004), http://dx .doi.org/10.1016/j.materresbull.2003.12.020. 18. S. C. Tjong and S. P. Bao, “Preparation and nonisothermal crystallization behavior of polyamide 6/montmorillonite nanocomposites,” J. Polym. Sci. Part B-Polym. Phys. 42(15), 2878–2891 (2004), http://dx.doi.org/10.1002/(ISSN)1099-0488. 19. M. Cadek et al., “Morphological and mechanical properties of carbon-nanotube-reinforced semicrystalline and amorphous polymer composites,” Appl. Phys. Lett. 81(27), 5123–5125 (2002), http://dx.doi.org/10.1063/1.1533118. 20. F. Du et al., “Nanotube networks in polymer nanocomposites: rheology and electrical conductivity,” Macromolecules 37(24), 9048–9055 (2004), http://dx.doi.org/10.1021/ma049164g. 21. D. E. Hill et al., “Functionalization of carbon nanotubes with polystyrene,” Macromolecules 35(25), 9466–9471 (2002), http://dx.doi.org/10.1021/ma020855r. 22. J. I. Hong et al., “Dielectric properties of zinc oxide/low density polyethylene nanocomposites,” Mater. Lett. 59(4), 473–476 (2005), http://dx.doi.org/10.1016/j.matlet.2004.10.036. 23. Z.-M. Dang, Y.-H. Zhang, and S.-C. Tjong, “Dependence of dielectric behavior on the physical property of fillers in the polymer-matrix composites,” Synth. Met. 146(1), 79–84 (2004), http://dx.doi.org/10.1016/j.synthmet.2004.06.011. 24. H. Zois, Y. P. Mamunya, and L. Apekis, “Structure and dielectric properties of a thermoplastic blend containing dispersed metal,” Macromol. Symp. 198(1), 461–472 (2003), http:// dx.doi.org/10.1002/(ISSN)1521-3900. 25. Z. Dang et al., “Dielectric properties and morphologies of composites filled with whisker and nanosized zinc oxide,” Mater. Res. Bull. 38(3), 499–507 (2003), http://dx.doi.org/10 .1016/S0025-5408(02)01055-3. 26. R. Gangopadhyay and A. De, “Conducting polymer nanocomposites: a brief overview,” Chem. Mater. 12(3), 608–622 (2000), http://dx.doi.org/10.1021/cm990537f. 27. E. A. Stern et al., “The UWXAFS analysis package: philosophy and details,” Physica B-Condensed Matter. 208(1–4), 117–200 (1995), http://dx.doi.org/10.1016/0921-4526(94)00826-H. 28. V. V. Matveev et al., “Cobalt nanoparticles with preferential hcp structure: a confirmation by X-ray diffraction and NMR,” Chem. Phys. Lett. 242(4–6), 402–405 (2005), http://dx.doi .org/10.1016/j.cplett.2006.02.099. Journal of Nanophotonics

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29. S. J. Oh, D. C. Cook, and H. E. Townsend, “Characterization of iron oxides commonly formed as corrosion products on steel,” Hyperfine Interact. 112(1–4), 59–65 (1998), http://dx.doi.org/10.1023/A:1011076308501. 30. C.-B. Ma et al., “Chi-carbide in tempered high carbon martensite,” Metall. Trans. A 14(6), 1033–1045 (1983), http://dx.doi.org/10.1007/BF02670442. 31. V. I. Goldanskii and R. H. Herber, Chemical Applications of Mössbauer Spectroscopy, Academic Press, London, New York (1968). 32. Y. A. Koksharov et al., “Hysteresis of the microwave absorption in polycrystalline ferromagnets,” Zh. Fiz. Chem. 73(10), 1862–1866 (1999) (in Russian). 33. R. M. Bozorth, Ferromagnetism, IEEE Press, New York, 735 (1993). 34. E. C. Stoner and E. P. Wohlfarth, “A mechanism of magnetic hysteresis in heterogeneous alloys,” Philos. Trans. R. Soc. London Ser. A 240(826), 599–642 (1948), http://dx.doi.org/ 10.1098/rsta.1948.0007. 35. R. W. Chantrell and K. O’Grady, “The magnetic properties of fine particles,” in Applied Magnetism, R.Gerber, C. D. Wright, and G. Asti, Eds., pp. 113–164, Kluwer Academic Publisher, Dordrecht-Boston-London (1994). 36. R. S. de Biasi and T. C. Devezas, “Anisotropy field of small magnetic particles as measured by resonance,” J. Appl. Phys. 49(4), 2466–2469 (1978), http://dx.doi.org/10.1063/1 .325093. 37. A. L. Efros, Physics and Geometry of Chaos, Nauka, Moscow (1982). 38. I. Balberg et al., “Percolation and tunneling in composite materials,” Int. J. Mod. Phys. 18(15), 2091–2121 (2004), http://dx.doi.org/10.1142/S0217979204025336.

Gleb Yurjevich Yurkov graduated from the N.G. Chernishevsky Saratov State University in 1998 and received his PhD in inorganic chemistry in 2002 at N.S. Kurnakov Institute of General and Inorganic Chemistry Russian Academy of Sciences. He received his doctor of sciences in technology in 2009. He is currently a leading researcher at the A.A. Baikov Institute of metallurgy and materials sciences of the Russian Academy of Sciences (IMET RAS) and general researcher at the All-Russian Scientific Research Institute of Aviation Materials (RIAM). His main research interests include inorganic chemistry, stabilization of nanoparticles, synthesis and study of homo- and heterometallic nanoparticles and composite materials composed of nanoparticles and polymer matrices. His research has been reported in more than 100 primary publications and summarized in 3 reviews, four books, five book chapters and 3 inventions. Alexander Sergeevich Fionov graduated from the Physical Department of the M.V. Lomonosov Moscow State University (MSU) in 1992 and received his PhD in technical science in 2012 at IMET RAS. He is currently a research worker at V.A. Kotel’nikov Institute of Radio Engineering and Electronics of the Russian Academy of Sciences (IRE RAS). His main research interests include stabilization of nanoparticles, synthesis and study of homo- and heterometallic nanoparticles and composite materials based on nanoparticles and polymer matrices, electrical, magnetic and microwave properties and applications of composite materials. His research has been reported in more than 12 articles in international and Russian scientific journals. Aleksander Vladimirovich Kozinkin is the head of the X-ray Spectroscopy Department, Institute of Physics of the Southern Federal University (IPSFU). He received his degree of PhD in physics and mathematics in 1983. Area of expertise is studies of electronic and atomic structure of nanoparticles stabilized in polymer matrices, chemical and charge states of atoms in nanoparticles, metal–metal bonds, chemical interactions of atoms of the nanoparticles with atoms of the polymers by x-ray emission, Mössbauer and XAFS spectroscopies. Journal of Nanophotonics

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Yury Alekseevich Koksharov currently a Docent of the general Physics Department of the MSU. He received the degree of PhD in physics and mathematics in 1991 at the MSU. His area of expertise is studies of electronic paramagnetic resonance of nanoparticles stabilized in polymer matrices, chemical and charge states of atoms in nanoparticles. His research has been reported in more than 200 articles in international and Russian journals, among these are several monographs and inventions.

Yevgeniy Anatolievich Ovtchenkov is currently a researcher at the low temperature Physics Department, the MSU. In 1993 he graduated from the MSU. He received the degree of PhD in physics and mathematics in 1997 at the MSU. His area of expertise is studies of magnetism of nanocomposite materials. His research has been reported in more than 30 articles in international and Russian journals.

Denis Alexandrovich Pankratov graduated from the Chemistry Department of the MSU in 1994. He received his PhD in chemistry in 1998 at Chemistry Department of the MSU. He is currently a leading researcher of the Radiochemistry Division of the Chemistry Department of the MSU, and associated professor of the Chemistry Department Moscow Pedagogical State University. His main research interests include the Mössbauer spectroscopy, solid state chemistry, coordination chemistry. His research has been reported in more than 40 articles in international and Russian scientific journals. Oleg Vladimirovich Popkov graduated the Higher Chemical College Russian Academy of Sciences in 2009. Since April 2012 he works as a junior researcher in IMET RAS. Science interests: nanoparticles, magnetic and optical properties of nanomaterials. O.V. Popkov is an author of 14 articles published in Russian and international journals.

Valery Grigorievich Vlasenko is the head of the Laboratory for X-ray Spectroscopy IPSFU. He received the degree of PhD in physics and mathematics in 1994. The basic scientific interests are characterization of advanced inorganic materials and metallocomplexes by XAFS, XRD and x-ray emission spectroscopies. He has published more than 100 articles in physics and chemistry scientific journals.

Yuriy Aleksandrovich Kozinkin is a researcher at the Laboratory of Condensed Matter Electronic Structure Theory, Theoretical Physics Department IPSFU. He received the degree of PhD in physics and mathematics in 2011. Research interests are condensed matter physics, x-ray and electron spectroscopy, computational physics.


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Marina Igorevna Biryukova graduated from Ivanovo State University in 2011. At the present time she is a PhD student at the IMET RAS. Her current research interests are in the fields of nanomaterials science and nanocomposites. Her research has been reported in two articles in Russian journals.

Vladimir Vladimirovich Kolesov graduated from the Physical Department of the MSU in 1974. He received his PhD in physical and mathematical science in 1985 at Physical Department of the MSU. He is currently a head of laboratory at IRE RAS. His main research interests include the molecular electronics, nanotechnology, nonlinear oscillations and waves, dynamical systems and chaos, signal processing, biomedical electronics, information technology. His research has been reported in more than 100 articles in international and Russian scientific journal and five inventions. Stanislav Vladimirovich Kondrashov graduated the Moscow Institute of Physics and Technology in 1982. He received his PhD in physical and mathematical science in 1986 at A.Yu.Ishlinsky Institute Problem in Mechanics Russian Academy of Sciences. He is currently a leading researcher at RIAM. His main research interests include the composite materials based on nanoparticles and polymer matrixes, as well as electrical, magnetic and microwave properties and applications of composite materials. Nikolai Alexandrovich Taratanov graduated from Ivanovo State University in 2006. He received his PhD in inorganic chemistry in 2010 at IMET RAS. At the present time lecturer, Department of Chemistry, theory of combustion and explosion in Ivanovo Institute of State Fire Service of EMERCOM of Russia. His current research interests are in the fields of nanomaterials science, composite, ceramics and inorganic chemistry. His research has been reported more than 25 articles in international and Russian scientific journals. Viacheslav Mikhailovich Bouznik graduated from the Tomsk State University in 1967. He received his PhD in physics and mathematics in 1972; doctor of sciences in chemistry in 1985; corresponding member of RAS in 1994; and full member of RAS in 1997. Worked in scientific organizations of Krasnoyarsk Science Center of Siberian Branch of RAS: Institute of Physics, Institute of Chemistry and Chemical Technology—1968 to 1990, Krasnoyarsk. Director of Institute of Chemistry of Far Eastern Branch of RAS—1990 to 1995, Vladivostok. Member of the Presidium of FEB RAS—1995 to 1996, Vladivostok. Since 1996—chairman of the Presidium of Khabarovsk Science Center FEB RAS, and head of fluoride materials laboratory in the Institute of Chemistry FEB RAS. He is currently a general researcher at the IMET RAS and RIAM. He is specialist in physical chemistry of inorganic materials, in nuclear-spectral methods of research. Scientific interests: nuclear-spectral methods of investigation of materials, sustainable development, small hi-tech business, small forms of production in scientific organizations. His research has been reported in more than 300 articles in international and Russian journals, among these are 3 monographs and 10 inventions.


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