184

ISSN 1995-0780, Nanotechnologies in Russia, 2008, Vol. 3, Nos. 3–4, pp. 184–190. © Pleiades Publishing, Ltd., 2008.Original Russian Text © A.S. Basaev, B.B. Bokhonov, O.F. Demidenko, V.A. Labunov, G.I. Makovetskii, E.L. Prudnikova, A.A. Reznev, A.N. Saurov, V.M. Fedosyuk, Yu.A. Fedot-ova, B.G. Shulitskii, K.I. Yanushkevich, 2008, published in Rossiiskie nanotekhnologii, 2008, Vol. 3, Nos. 3–4.

INTRODUCTION

Carbon nanotubes are carbon molecules with aunique combination of specific mechanical, electrical,emission, optical, and chemical properties. Over thelast fifteen years, these objects have not ceased toamaze with regularly revealed new effects and applica-tions [1].

A substantial step forward in the development ofnanotechnologies is the use of carbon nanotubes filledwith nanoparticles consisting of different materials.The resulting nanocomposites exhibit properties ofboth encapsulated and encapsulating materials withpromising synergetic effects. This leads to a consider-able additional contribution to the potentialities of theiruse in microelectronic and nanoelectronic devices [2].

One of the promising directions in this field is theinvestigation of the properties of carbon nanotubescombined with magnetic materials [3], because therearises a possibility of synthesizing magnetically func-tionalized carbon nanotubes, in particular, multiwall car-bon nanotubes filled with ferromagnetic nanoparticles.

Nanostructuring of a massive magnetic materialsubstantially affects its magnetic properties. For exam-ple, the coercive force decreases, while the magneticpermittivity and the saturation magnetization increasewith a decrease in the grain size to 40–20 nm. Thiseffect is enhanced in the case of very small grain sizes(on the order of one domain). As a consequence, themagnetic vectors of atoms in an external magnetic fieldare identically oriented within a grain, thus eliminatinglosses through the domain walls and neighboringdomains with different magnetization directions. Mate-rials with grains of this size can have no hysteresis andpossess superparamagnetic properties.

When single-domain ferromagnetic nanoparticlesare embedded in a nonmagnetic matrix, this matrixweakens the magnetic interaction between nanoparti-cles and, hence, decreases the magnetic field requiredto reorient their magnetic moments. These nanocom-posites are characterized by a giant magnetoresistance.This has opened up new possibilities for their practicalapplications, for example, in sensitive elements of mag-netometers and magnetic read heads.

Synthesis and Propertiesof Magnetically Functionalized Carbon Nanotubes

A. S. Basaev

a

, B. B. Bokhonov

b

, O. F. Demidenko

c

, V. A. Labunov

d

, G. I. Makovetskii

c

, E. L. Prudnikova

d

, A. A. Reznev

e

, A. N. Saurov

a

, V. M. Fedosyuk

c

, Yu. A. Fedotova

f

, B. G. Shulitskii

d

, and K. I. Yanushkevich

c

a

Scientific and Manufacturing Complex “Technological Centre,” Moscow Institute of Electronic Technology (Technical University), Zelenograd, Moscow oblast, 124498 Russia

e-mail: as@tcen.ru

b

Institute of Solid-State Chemistry and Mechanochemistry, Siberian Branch, Russian Academy of Sciences,ul. Kutateladze 18, Novosibirsk, 630128 Russia

c

Institute of Solid-State and Semiconductor Physics, Belarussian Academy of Sciences, ul. Brovki 17, Minsk, 220072 Belarus

d

Belarussian State University of Informatics and Radioelectronics, ul. Brovki 6, Minsk, 220013 Belarus

e

Research Institute, Federal Security Service, Moscow, Russia

f

National Scientific and Educational Centre of Particle and High-Energy Physics, Belarussian State University,ul. Bogdanovicha 153, Minsk, 220040 Belarus

Received November 12, 2007; in final form, November 28, 2007

Abstract

—This paper reports on the results of a complex investigation of the crystal structure, the composition,and the specific magnetization of magnetically functionalized multiwall carbon nanotubes. The carbon nano-tubes are synthesized by the high-temperature pyrolysis of liquid hydrocarbon

p

-xylene C

8

H

10

in a mixture witha volatile catalyst, namely, ferrocene Fe(C

5

H

5

)

2

, on the surface of silicon substrates in a quartz reactor. Underthe synthesis conditions used in the experiment, arrays of vertically aligned nanotubes are formed on the siliconsubstrates and reactor walls. It is established that carbon nanotubes of both types exhibit identical propertiesand represent a complex nanocomposite, C–Fe

3

C–Fe

5

C

2

–Fe. An analysis of the temperature dependences ofthe specific magnetization

σ

=

f

(

T

) demonstrates that, in the temperature range 78 K

≤

T

≤

1060 K, the magneticproperties of the nanotubes under investigation are governed by the properties of iron carbides (in the form ofFe

3

C and Fe

5

C

2

) and iron. It is revealed that the synthesized carbon nanotubes possess reversible magneticproperties in the temperature range 78 K

≤

T

≤

720 K.

DOI:

10.1134/S199507800803004X

EXPERIMENT

NANOTECHNOLOGIES IN RUSSIA

Vol. 3

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SYNTHESIS AND PROPERTIES 185

Therefore, considerable progress can be made, forexample, in increasing the capacity of magnetic read–write devices owing to the use of magnetically functional-ized carbon nanotubes prepared by filling of carbon nano-tubes with ferromagnetic nanoparticles. In this case, theparticle size can be small enough for these particles to besingle domain and the carbon nanotube walls serve as non-magnetic separating regions between nanoparticles.

The purpose of this work was to synthesize multiwallcarbon nanotubes with the use of iron nanoparticles as agrowth catalyst and to perform detailed investigations oftheir crystal structure, the composition, and the specificmagnetization over a wide range of temperatures.

SYNTHESIS OF MAGNETICALLY FUNCTIONALIZED CARBON NANOTUBES

There are several techniques for introducing a mate-rial into carbon nanotube cavities [2]. One of the tech-niques is conventional evaporation of carbon in an arcdischarge with the use of an anode containing the mate-rial that should be encapsulated. For the most part, thistechnique is applicable to materials that can “survive”under extreme conditions of electric arc discharge. Thesecond technique consists in chemically opening theends of closed nanotubes, followed by introducing afiller compound inside nanotubes due to the capillaryeffect. This method proved to be better than the firsttechnique and can be used for incorporating fillers frommelts (liquid phases) and even in the case of biologicalmolecules. The third technique involves the synthesisof carbon nanotubes through the high-temperaturepyrolysis of liquid hydrocarbons in a mixture with avolatile catalyst providing the growth of carbon nano-tubes. Catalyst nanoparticles deposit on a substrate andinitiate the growth of carbon nanotubes. Moreover, dur-ing growth they are embedded in carbon nanotubesover their entire length and even occupy the ends of thenanotube. It is surprising that the catalysts for carbonnanotube growth are the ferromagnetic materials Fe,Ni, and Co. Consequently, this technique is most appro-

priate for synthesizing magnetically functionalized car-bon nanotubes. It is this technique that was used in ourwork for preparing multiwall carbon nanotubes withthe aim of filling their free volume with particles ofiron, which is the most widely used magnetic com-pound among the triad of iron, cobalt, and nickel.

Carbon nanotubes were synthesized by high-tem-perature pyrolysis of liquid hydrocarbon

p

-xyleneC

8

H

10

in a mixture with volatile ferrocene [Fe(C

2

H

5

)

2

]as a catalyst at atmospheric pressure with the use ofargon as a gas carrier on the surface of silicon substrates[KDB 20 (100)] in a tubular quartz reactor speciallydesigned for these purposes [4]. The samples for inves-tigations were prepared under conditions of predomi-nant growth of carbon nanotubes on the Si substrates[5]: the ferrocene concentration in

p

-xylene was 10%,the mixture injection rate into the reactor zone was1 ml/min, the temperature was 870

°

, the argon flow ratewas 100 cm

3

/min, and the reaction time was 5 min.Under these synthesis conditions, carbon nanotube

arrays were formed on the silicon substrates and reactorwalls. The external appearance of the carbon nanotubearrays is shown in Fig. 1.

It can be seen from Fig. 1 that the array of verticallyaligned close-packed carbon nanotubes is formed underthe aforementioned synthesis conditions. Bright inclu-sions against the dark background of the array cleavagewall (Fig. 1a) and the array surface are characteristicsof the image. The carbon nanotubes located at the cen-ter of the array cleavage wall are shown in Fig. 1b. Itcan be seen that the carbon nanotubes are broken andbent. The bending of the carbon nanotubes can suggestthat, in the array, there are internal stresses, which leadto deformation of nanotubes after cleavage. Brightinclusions are clearly seen at the ends of broken carbonnanotubes. This indicates the presence of metal-con-taining particles. Rather long bright arc regions in theimage of the nanotube array can result from illumina-tion upon focusing of the electron beam of the micro-scope. Since metal-containing segments of nanotubesare observed at the center of the height of the array, we

2.5

μ

m 0.5

μ

m 0.5

μ

m(a) (b) (c)

Fig. 1.

Images of carbon nanotubes synthesized on Si substrate and on the walls of a quartz reactor: (a) axonometric view of carbonnanotube arrays (vertical wall of array cleavage and array surface), low magnification; (b) vertical wall of array; and (c) carbonnanotube array surface, high magnification.

186

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et al.

can assume that they are also located inside the carbonnanotubes along their entire length. As can be seenfrom Fig. 1c, disordered nanostructures of differentconfigurations are formed at the array surface. Thisphenomenon is typical of the synthesis of carbon nano-tubes through the high-temperature pyrolysis of liquidhydrocarbons in a mixture with a volatile catalyst. Atthe instant of completion of pyrolysis synthesis, thesynthesis conditions change abruptly, deviate fromoptimum, and prevent orientated growth of carbon nan-otubes. The presence of bright regions in the image ofthe array surface also indicates that metal-containingnanoparticles are contained at the surface.

X-RAY DIFFRACTION DATA

X-ray diffraction analysis of the carbon nanotubes syn-thesized on the Si substrates and formed at the walls of thequartz reactor was performed at room temperature. TheX-ray diffraction data (Cu

K

α

radiation) were collected bypoint sampling with an angle step of

Δ

2

θ

= 0.03

°

. Theexposure time per each angle point was

Δτ

= 5 s.The X-ray diffraction patterns of the carbon nano-

tubes of both types are depicted in Fig. 2. For the car-bon nanotubes synthesized on the silicon substrate, theX-ray diffraction pattern (Fig. 2a) in the angle range5

°

≤

2

θ

< 30

°

contains a set of low-intensity reflectionsthat can be assigned to amorphized carbon in the com-position of the soot and graphite.

The X-ray diffraction pattern in the angle range30

°

< 2

θ

≤

80

°

involves high-intensity reflection (400)from the Si substrate a series of low-intensity reflec-tions that can be used for determining the compositionof the composite under investigation. Somewhat unex-pectedly, the identification of the X-ray diffraction pat-terns revealed that Fe

3

C cementite is the main compo-nent of carbon nanotubes. The reflections indexed as(112), (201), (211), (122), (004), (222), and (313) forFe

3

C cementite are clearly seen in the X-ray diffraction

pattern. Iron Fe in the form of the (110) and (200)reflections and the Fe

5

C

2

carbide in the form of the(021) reflection manifest themselves in the X-ray dif-fraction pattern. It is known that the crystal structure inthe most accurate and compact form is represented inX-ray powder diffraction patterns [6]. The carbon nan-otubes deposited on the reactor walls were mechani-cally separated from the walls in the form of a pow-dered material. The X-ray powder diffraction pattern ofthe carbon nanotube powder (Fig. 2b) contains a halo ofamorphized carbon at small angles 2

θ

and a pro-nounced (111) reflection of graphite with a rhombohe-dral structure (ICDD card no. 75-2078, PCPDFWIN)[7]. This structure is characteristic of carbon nanotubes.At larger angles, the X-ray powder diffraction patternexhibits a series of lines corresponding to the Fe

3

C, Fe,and Fe

5

C

2

phases, the intensities of which are consider-ably higher than those of lines shown in Fig. 2a.Analysis of the X-ray powder diffraction pattern inFig. 2b also demonstrates that the Fe

3

C cementite withan orthorhombic structure (space group Pbnm) domi-nates over the other components in the sample underinvestigation. A comparison between the areas of thereflections (with allowance made for the overlappingreflections) shows that the Fe

3

C content in the compos-ite with respect to the Fe and Fe

5

C

2

contents is morethan 90%. By using the techniques for identifying theorthorhombic structure and its quadratic form [6]

(1)

we determined the unit cell parameters of the Fe

3

Cphase in the carbon nanotubes. It should be noted thatthe numbers of the reflections corresponding to theFe

3

C phase in the X-ray diffraction patterns in Figs. 2aand 2b are sufficient for this purpose. The calculatedunit cell parameters are as follows:

a

= 0.452 nm,

b

=0.508 nm, and

c

= 0.672 nm. This is in good agreement

θhklsin2 λ2

4a2--------h2 λ2

4b2--------k2 λ2

4c2--------l2,+ +=

806040200

60

40

20

(a)

Fe

3

C(1

12)

Fe

3

C(2

01)

Fe

5

C

2

(021)

Fe(

110)

Fe

3

C(2

11)

Fe

3

C(1

22)

Fe

3

C(0

04)

Fe

3

C(2

22)

Fe

3

C(3

13)

Si(400)

Intensity

2

θ

Substrate

10080604020

(b)

2θ

300

200

100

Intensity

Am

orp

hous

C

Gra

phit

e(111)

Fe 3

C(2

01)

Fe 3

C(1

12)

Fe 3

C(1

20)

Fe 3

C(0

22)

+ F

e 5C

2(0

21)

Fe 3

C(1

03)

Fe(

100)

Fe 3

C(1

22)

Fe 3

C(1

30)

Fe(

200)

Fe 3

C(2

31)

Fe 3

C(2

32)

(140)

+ F

e 3C

(313)

Fe 3

C(1

25)

Fe 3

C(0

06)

Fe 3

C(0

43)

Fig. 2. XRD patterns of carbon nanotubes: (a) synthesized on Si substrates and (b) quartz reactor walls.

NANOTECHNOLOGIES IN RUSSIA Vol. 3 Nos. 3–4 2008

SYNTHESIS AND PROPERTIES 187

with the corresponding unit cell parameters a = 4.518 Å,b = 5.069 Å, and c = 6.736 Å available in the ICDD data-base (card nos. 76-1877 and 75-0910, PCPDFWIN) [7]for the polycrystalline compound Fe3C.

The results are undeniably of theoretical and practi-cal interest. The dominance of the Fe3C cementite in thecomposition of the carbon nanotubes indicates that,during their growth, Fe catalyst particles are not onlyembedded in the carbon nanotube, they also interactwith the nanotube with the formation of the stable com-pound Fe3C, which in the massive polycrystalline formpossesses pronounced ferromagnetic properties. Fromthe practical viewpoint, this will make it possible to usemagnetically functionalized carbon nanotubes for fab-ricating reliable microelectronic and nanoelectronicdevices resistant to external actions.

ELECTRON MICROSCOPIC DATA

The carbon nanotubes formed on quartz reactorwalls where investigated by transmission electronmicroscopy. For this purpose, the carbon nanotubeswere dispersed on a carbon microgrid of a high-resolu-tion electron microscope.

The experimental results are presented in Fig. 3. It isknown that electron diffraction patterns of carbon nan-otubes, especially when they are obtained for multiwallnanotubes, are difficult to interpret [2]. However, qual-itative analysis of the electron diffraction patterns of thesamples under investigation (Fig. 3a) demonstrates agood correlation with the X-ray diffraction data. Thehalo associated with the amorphized carbon is rather pro-nounced. The electron diffraction pattern contains (002)and (004) reflections of the graphite. Possibly, thesereflections overlap with the (002) and (004) reflectionsof the cementite (PDF no. 76-1877). This is the mostreal situation, because, according to the contrast, allinclusions in nanotubes are nanocrystals and, hence,should also be characterized by point reflections. More-over, it is clear that a coherent interface (002)graphite II(002 should occur between the graphite and the

carbide. As regards ring reflections, they can be associ-ated with the graphite. Furthermore, the weak reflec-tions (110) and (211) attributed to the iron particles areobserved in the electron diffraction pattern. The imageof the array of misoriented carbon nanotubes is dis-played in Fig. 3b. It can be seen from this figure that a

)Fe3C

211Fe

004Fe3C

002Fe3C

002Fe3C

004Fe3C

110Fe

100 nm

30 nm

20 nm

Channel

Carbon-encapsulated

nanoparticles

(a) (b)

(c) (d)

Fig. 3. Electron microscopic data: (a) electron diffraction pattern, (b) general view of disordered carbon nanotube array, and(c, d) fragments of two nanotubes and a nanocapsule.

188

NANOTECHNOLOGIES IN RUSSIA Vol. 3 Nos. 3–4 2008

BASAEV et al.

large number of black dots and horizontally locatednanotubes occur in the image. The black dots can cor-respond either to filler particles at the ends of the nano-tubes located perpendicular to the substrate or to mag-netic nanoparticles encapsulated by carbon. It is evi-dent that filler nanoparticles are characterized by aconsiderable size dispersion. It should be noted that thesize of encapsulated particles exceeds their size in nan-otubes and lie in the range ~40–50 nm. The diameter ofthe nanotubes located in the horizontal plane varies from~5 to ~40 nm. The original images in which it is possibleto see both nanotubes and nanocapsules are displayedin Figs. 3c and 3d. It can be seen from these figures thatthe nanotubes are multiwall and their outside diametervaries from ~20 to ~40 nm. The diameter of filler nano-particles is smaller and ranges from ~5 to ~20 nm. Thetwo nanotubes and a dumbbell-like nanocapsule areclearly seen in Fig. 3c. One of the nanotubes has anempty channel, and the other nanotube is filled withoval nanoparticles (~5–20 nm in diameter) separated bywalls. A carbon nanotube array fragment also involvingtwo nanotubes and a nanocapsule is shown in Fig. 3d.In this case, too, one nanotube has an empty channeland the neighboring nanotube contains elongated nano-particles ~5 nm in diameter and ~80 nm in length.

Therefore, investigations of carbon nanotubes bytransmission electron microscopy permitted us to deter-mine the ranges of the nanotube and filler particle sizes.It was established that filler inclusions in the carbonnanotubes have different configurations and differentsizes and are differently embedded in the nanotubes.Analysis of the electron microscope images demon-strated that the outside diameters of multiwall carbonnanotubes and filler particles (located inside nanotubes)are characterized by a large size dispersion. Moreover,it was revealed that the samples contain an insignificantnumber of single-wall carbon nanotubes.

RESULTS OF THE INVESTIGATION OF THE TEMPERATURE DEPENDENCES

OF THE SPECIFIC MAGNETIZATION

The specific magnetization of the magneticallyfunctionalized carbon nanotubes was measured by thestatic ponderomotive method [8]. The dependences σ =f(T) were obtained in the temperature range 78 K ≤ T <1100 K in the magnetic field H = 0.86 T (the magneticfield gradient across a sample region ΔZ ≈ 3.0 cm wasdHZ/dx ≈ 0.16 T cm–1). The temperature dependencesσ = f(T) were measured upon heating of the samplesfrom liquid-nitrogen temperature and upon coolingfrom the maximum temperature Tmax to room tempera-ture. The dependences σ = f(T) for the nanotube pow-ders over the entire temperature range under investiga-tion are plotted in Fig. 4. The temperature dependenceσ = f(T) upon heating clearly reflects a sequence ofmanifestations of all magnetic phases of the filler in thecarbon nanotubes and a variation in their specific mag-netization with an increase in the temperature. The firstanomalous point in the dependence σ = f(T) correspondsto the Curie point TC ~ 480 K for the Fe3C cementite [9].The specific magnetization in the temperature range500–750 K is determined by the total contribution ofthe Fe5C2 carbide and iron nanoparticles. A comparisonof the specific magnetizations for the Fe3C cementite at78 K and a temperature below its Curie point enables usto estimate the contribution of the cementite to the totalmagnetization associated with all the iron-containingphases. Analysis of the experimental temperaturedependences σ = f(T) shows that the cementite contentin the filler of the sample under investigation is morethan 90%. The dependence σ = f(T) in the temperaturerange 850–940 K upon heating reflects an increase in thespecific magnetization due to the increase in the size ofiron particles. The measured specific magnetizations wereused to calculate the magnetic moments of the samples atdifferent temperatures. The magnetic moment μ and thespecific magnetization σ are related by the expression

, (2)

where M is the molar weight, NA is the Avogadro num-ber, and μB is the Bohr magneton.

According to the calculation, the magnetic momentof iron in the cementite at a temperature of 78 K is μ =0.64μB. The low magnetic moment of iron in the cement-ite can be associated with the fact that the nanotubescontain Fe3C inclusions with sizes less than the size ofsingle-domain particles. In the temperature range 500–750 K, a magnetic moment of approximately 0.12μBcharacterizes the “metastable carbide Fe5C2–Fe” com-posite. The magnetic moment of iron in the nanotubesat a temperature of 850 K is μ = 0.008μB. This low mag-netic moment of iron at 850 K can also be explained bythe fact that the majority of Fe particles have sizes lessthan 14 nm [10]. Further heating leads to a drasticincrease in the magnetic moment of iron by one order

μ σMNA---------μB=

1000800600400200T, K

24

22

20

18

16

14

12

10

8

6

4

2

0

σ, Gcm3g–1

HeatingCooling

TC Fe3C

TC Fe

Fig. 4. Temperature dependences σ = f(T) for powder mag-netically functionalized carbon nanotubes in cooling andheating.

NANOTECHNOLOGIES IN RUSSIA Vol. 3 Nos. 3–4 2008

SYNTHESIS AND PROPERTIES 189

of magnitude, most likely due to the increase in the sizeof Fe particles upon sintering. At a temperature of 940 K,the magnetic moment is calculated to be μ = 0.086μB.Heating of the sample to temperatures above 940 Kresults in a decrease in the magnetic moment to zero atthe Curie point of 1060 K for iron. Since the increase inthe size of Fe particles with an increase in the tempera-ture is irreversible, the temperature dependence of thespecific magnetization upon cooling of the sample toroom temperature should not coincide with the depen-dence σ = f(T) upon heating. This is actually observed forthe dependence σ = f(T) obtained upon cooling (Fig. 4).

MÖSSBAUER SPECTROSCOPIC DATA

Mössbauer spectroscopy is an effective method forinvestigating the atomic and magnetic structures of sol-ids [11, 12]. The 57Fe Mössbauer spectrum of the car-bon nanotubes with a natural abundance of 57Fe nucleiin the iron-containing filler at T = 300 K is depicted inFig. 5. The analysis of the experimental spectrum dem-onstrates that the Mössbauer spectrum contains at leastthree sextets associated with the magnetic Zeemansplitting and one singlet. The well-resolved sextet withan effective magnetic field Heff ~ 200 kOe and an iso-mer shift of ~0.3 mm/s corresponds to the 57Fe nuclei inthe Fe3C cementite. According to the calculations, theexperimental spectrum also contains two additionalsextets with lower intensities. Their effective magneticfields are 170–180 and 100–110 kOe. These effectivemagnetic fields are characteristic of the Mössbauerspectra of Fe5C2 iron carbide [13, 14]. The isomer shiftof the singlet in the Mössbauer spectrum is zero. Thisindicates that the carbon nanotubes involve particles(~5%) containing 57Fe nuclei in the superparamagneticstate [12]. The calculation of the contributions from thesubspectra of the Fe3C, Fe5C2, and Fe phases to the totalMössbauer spectrum demonstrates that the contributionof the Fe3C sublattice is approximately 90%. This find-ing obtained from the Mössbauer spectroscopic data isin good agreement with the results of X-ray diffractionanalysis and measurements of the specific magnetiza-tion. Moreover, the inference made from the experimen-tal Mössbauer spectroscopic data that a certain numberof filler particles in the carbon nanotubes are in the super-paramagnetic state is also of particular importance.

CONCLUSIONS

Thus, multiwall carbon nanotubes were synthesized byhigh-temperature pyrolysis of p-xylene C8H10 in a mixturewith ferrocene [Fe(C5H5)2] on silicon substrates.

It was established that arrays of vertically alignedclose-packed nanotubes are formed on silicon substratesunder the synthesis conditions used. Arrays identical instructure and composition are also formed on the quartzwalls of the reactor used for nanotube synthesis.

The C–Fe3C–Fe5C2–Fe composition of the synthe-sized composites was determined using different exper-imental methods.

It was revealed that Fe3C, Fe5C2, and Fe filler nano-particles are characterized by a large size dispersion (5–40 nm).

The analysis of the results of X-ray diffractionresults, measurements of the specific magnetization,and Mössbauer spectroscopy demonstrated that theFe3C content in the filler of the carbon nanotubes isapproximately 90%.

The unit cell parameters for the structure of theFe3C phase in the nanotubes were determined to bea = 0.452 nm, b = 0.508 nm, and c = 0.672 nm.

The analysis of the experimental data on the specificmagnetization showed that the synthesized carbon nan-otubes containing the Fe3C–Fe5C2–Fe filler possessreversible magnetic properties in the temperature range78 K ≤ T ≤ 720 K.

The effective magnetic fields on 57Fe nuclei in thecomposition of the filler components were determined.

It was revealed that a certain number of filler parti-cles in the carbon nanotubes possess superparamag-netic properties.

REFERENCES

1. P. N. D’yachkov, Carbon Nanotubes: Structure, Proper-ties, and Applications (BINOM—Laboratoria Znanii,Moscow, 2006), p. 293 [in Russian].

2. P. J. F. Harris, Carbon Nanotubes and Related Structures(Cambridge University Press, Cambridge, 2002; TEKh-NOSFERA, Moscow, 2003), p. 336.

3. Ch. P. Poole, Jr. and F. J. Owens, Introduction to Nano-technology (Wiley, New York, 2003; TEKhNOSFERA,Moscow, 2005), p. 336.

86420–2–4–6–8Velocity, mm/s

1.0000

0.9995

0.9990

0.9985

0.9980

0.9975

0.9970

0.9965

0.9960

Intensity, %

Fe3CFe5C2

TFe

Fig. 5. Mössbauer spectrum of 57Fe nuclei in magneticallyfunctionalized carbon nanotubes at 300 K.

190

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4. V. A. Labunov and V. G. Shulitski, “Nonrestricted LargeArea of Vertically Aligned Carbon Nanotubes,” in Pro-ceedings of the III Russian–Japanese Seminar“Advanced Technological Processes, Materials, andEquipment for Production of Solid-State ElectronicsElements and Nanomaterials MISiS–ULVAC,” Moscow,Russia, April 11–12, 2005, Ed. by L. V. Kozhitov (Mos-cow State Institute of Steel and Alloys (MISiS), Mos-cow, 2005), p. 260.

5. V. A. Labunov, B. G. Shulitski, and E. L. Prudnikava,“High-Efficiency Method of Selective CNT Arrays Growthon the Metal/Dielectric/Semiconductor Substrates forFEDs Application,” in Digest of Technical Papers of theInternational Symposium, Seminar and Exhibition(SID-2006), Moscone Center, San Francisco, California,United States, June 4–9, 2006 (Society for Information Dis-play, San Francisco, 2006), pp. 644–647.

6. H. Lipson and H. Steeple, Interpretation of X-ray Pow-der Diffraction Patterns (Macmillan, London, 1970;Mir, Moscow, 1972), p. 384.

7. Joint Committee on Powder Diffraction Standards—International Centre for Diffraction Data (JCPDS—ICDD), PCPDFWIN, Version 2.00, 1998.

8. V. I. Chechernikov, Magnetic Measurements (MoscowState University, Moscow, 1969), p. 387 [in Russian].

9. S. Chikazumi, Physics of Ferromagnetism (MagneticProperties of Materials) (Syokabo, Tokyo, 1980; Mir,Moscow, 1983).

10. P. A. Chernavskii, Ross. Khim. Zh. 46 (3), 19 (2002).

11. I. P. Suzdalev, Dynamic Effects in Mössbauer Spectros-copy (Atomizdat, Moscow, 1979), p. 192 [in Russian].

12. V. V. Ovchinnikov, Mössbauer Methods in Analysis ofAtomic and Magnetic Structures of Alloys (FIZMATLIT,Moscow, 2002), p. 256 [in Russian].

13. V. I. Gol’danskii, Chemical Applications of MössbauerSpectroscopy (Academic, New York 1968; Mir, Moscow,1970), p. 164.

14. B. B. Bokhonov, G. I. Makovetskii, K. I. Yanushkevich,et al., Fiz. Tekh. Vys. Davlenii 15 (3), 84 (2005).