Reactivity of metal-containing monomers 70.* Preparation and magnetic properties of metal-containing nanocomposites

Article abstract of DOI:10.1007/s11172-011-0220-x

Nanocomposites containing magnetically active nanoparticles stabilized by the carbon-containing matrix formed in parallel were obtained by the polymerization - destruction synthesis. The composition, structure, and magnetic properties of nanocomposites sy

Full text of DOI:10.1007/s11172-011-0220-x

1
476
Russian Chemical Bulletin, International Edition, Vol. 60, No. 7, pp. 1476—1487, July, 2011
Reactivity of metalꢀcontaining monomers
7
0.* Preparation and magnetic properties of metalꢀcontaining nanocomposites
A. D. Pomogailo,a G. I. Dzhardimalieva, A. S. Rozenberg, V. A. Shershnev, and M. Leonowiczb
a
a†
a
aInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1
prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Eꢀmail: adpomog@icp.ac.ru
Faculty of Materials Science and Engineering, Warsaw University of Technology,
b
Woloska 141, 02ꢀ507 Warsaw, Poland.
Eꢀmail: mkl@inmat.pw.edu.pl
Nanocomposites containing magnetically active nanoparticles stabilized by the carbonꢀ
containing matrix formed in parallel were obtained by the polymerization—destruction syntheꢀ
sis. The composition, structure, and magnetic properties of nanocomposites synthesized by the
II
II
thermal decomposition of unsaturated metal carboxylates and transition metal (Co , Ni ,
III
Fe ) acrylamide complexes were studied by powder Xꢀray diffraction, scanning and transmisꢀ
sion electron microscopy, and Mössbauer spectroscopy. The key macro stages and kinetic
features of thermolysis of the metalꢀcontaining monomers were identified. The variation of the
conditions of thermal transformations allows one to control the magnetic properties of nanoꢀ
composites from ferromagnetic to superparamagnetic behavior.
Key words: metal nanoparticles, magnetic properties, metalꢀcontaining nanocomposites,
exchange anisotropy.
Magnetic and semiconductor nanoparticles are attracꢀ
Experimental
tive investigation objects because the major contribution
to the formation of their physicochemical characteristics
is made the quantumꢀsize effect. The considerable interest
in the dꢀelement nanoparticles is caused by their specific
Unsaturated metal carboxylates and acrylamide complexes
II
II
III
of Co , Ni , and Fe nitrates were synthesized and characterꢀ
9,10
ized as described previously.
All of the obtained metalꢀconꢀ
2
magnetic properties and the possible design of high density
taining monomers were solid powders.
3
magnetic recording media. Magnetic particles are widely
Cobalt(II) acrylate. Found (%): C, 32.6; H, 3.7; Co, 27.5.
4
—6
(
2
1
CH =CHOCO) Co•H O. Calculated (%): C, 32.9; H, 3.6; Co,
used in biomedicine,
and the role of iron (magnetite
2 2 2
–
1
6.9. IR (KBr pellet), ν/cm : 1640 (C=C); 1065 (=CH—C);
360, 1560 (COO); 280 (M—O).
and maghemite) having high biocompatibility is especialꢀ
ly important. Ironꢀ and cobaltꢀcontaining particles have
high coercive force and magnetic susceptibility values; for
example, saturation magnetization (σ , M ) of the magnetite
Nickel(II) acrylate. Found (%): C, 32.40; H, 3.7; Ni, 26.7.
(
CH =CHOCO) Ni•H O. Calculated (%): C, 32.9; H, 3.6;
2 2 2
s
s
–1
Ni, 26.9. IR (KBr pellet), ν/cm : 1640 (C=C); 1065 (=CH—C);
1360, 1560 (COO); 290 (M—O).
–
1
–1 7
Fe O is 92 emu g and that of γꢀFe O is 74 emu g
,
3
4
2
3
and the coercive force for the anisotropic nanoparticles of
Iron(III) acrylate. Found (%): C, 31.7; H, 3.7; Fe, 24.6.
[Fe O(CH =CHOCO) •3H O]OH. Calculated (%): C, 31.9;
8
the latter varies from 200 to 400 Oe. However, a considꢀ
3
2
6
2
–
1
erable drawback is the tendency of nanoparticles for agꢀ
gregation and oxidation, which changes their magnetic
properties. Therefore, development of efficient methods
for stabilization of magnetic nanoparticles and approaches
to control of their composition and structure depending on
the nature of the metalꢀcontaining monomer is a topical
task, and this is the subject of the present study.
H, 3.1; Fe, 24.5. IR (KBr pellet), ν/cm : 1635 (C=C); 1370,
1
575 (COO); 525 (M—O).
Cobalt maleate(II). Found (%): C, 21.5; H, 2.2; Co, 28.5.
(
OCOCH=CHOCO) Co•2H O. Calculated (%): C, 23.0; H, 2.9;
2 2
–
1
Co, 28.2. IR (KBr pellet), ν/cm : 1638 (C=C); 1366, 1435
(
COO); 280 (M—O).
Iron(III) nitrate acrylamide complex. Found (%): C, 27.4;
H, 3.7; Fe, 10.6; N, 18.6. Fe(NO ) (CH =CHCONH ) .
3
3
2
2 4
Calculated (%): C, 27.0; H, 4.7; N, 16.5; Fe, 10.9. IR (KBr
1
*
†
For Part 69, see Ref. 1.
Deceased.
pellet), ν/cm– : 3190, 3320 (NH); 1660 (CO); 1385 (NO );
280 (M—O).
3
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1453—1463, July, 2011.
066ꢀ5285/11/6007ꢀ1476 © 2011 Springer Science+Business Media, Inc.
1

Reactivity of metalꢀcontaining monomers
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1477
Cobalt(II) nitrate acrylamide complex. Found (%): C, 29.5;
of the metalꢀcontaining groups of the resulting polymer to
H, 4.9; Co, 11.8; N, 15.6. Co(NO ) (CH =CHCONH ) •
12,13
3
2
2
2 4
give a metalꢀcontaining phase.
analysis data, dehydration of the monomeric crystal
hydrates, for example, acrylic acid salts, occurs at Texp
353—487 K ([Fe O(CH =CHOCO) •3H O]OH,
According to thermal
•
2H O. Calculated (%): C, 28.6; H, 5.0; Co, 11.7, N, 16.7. IR
2
–
1
(
3
KBr pellet), ν/cm : 3190, 3290 (NH); 1665 (CO); 1385 (NO );
3
=
54 (M—O).
=
3
2
6
2
Nickel(II) nitrate acrylamide complex. Found (%): C, 29.7;
Fe OAcr ), 413—453 K (Co(CH =CHOCO) •H O,
H, 5.2; N, 15.2; Ni, 11.1. Ni(NO ) (CH =CHCONH ) •
3
6
2
2
2
3
2
2
2 4
CoAcr ), 373—473 K (Ni(CH =CHOCO) •H O, NiAcr ),
•
2H O. Calculated (%): C, 28.6; H, 5.0; N, 16.7; Ni, 11.7. IR
2
2
2
2
2
2
–
1
and
that
of
the
acrylamide
complex
(
KBr pellet), ν/cm : 3195, 3290 (NH); 1665 (CO); 1385 (NO );
3
3
54 (M—O).
[Co(CH =CHCONH ) (H O) ](NO ) (CoAAm) occurs
2 2 4 2 2 3 2
Nanocomposites were prepared by controlled thermolysis
at 328—362 K. The increase in the temperature of the
dehydrated monomer to Texp = 473—573 K induces solidꢀ
phase polymerization. In this temperature region, in addiꢀ
tion to the insignificant weight loss by the sample (<10 wt. %),
slight gas evolution occurs. In the case of metal acrylates,
of metalꢀcontaining monomers in the isothermal mode at
43—1073 K in a selfꢀgenerated atmosphere by a reported proꢀ
6
1
1
cedure. The thermolysis gave finely dispersed darkꢀbrown or
black powders with the specific surface area (the thermolysis
temperature, K, is in parentheses) S = 36.7 (653), 29.5 (633),
sp
2
–1
II
II
III
the major gas components are CO and H C=CHCOOH
1
5 (643), and 30.0 m g (643) for the Co , Ni , and Fe
acrylates and Co maleate, respectively. According to elemenꢀ
tal analysis data, for example, the product of thermolysis of the
2 2
II
and HOOCCH=CHCOOH vapors, which condense
at room temperature on the reactor walls. Characteristic
II
acrylamide complex of Co nitrate at 673 K has the following
temperatures of polymerization are ∼ 543 K (CoAcr ),
2
composition (wt %): C, 37.0; H, 2.6; N, 8.7; the residue is 48.8
∼ 563 K (NiAcr ), ∼ 518 K (Fe OAcr ), and 488—518 K
2
3
6
(
in relation to Co 38.4%), the matrix after removal of the metal:
(
Co[OOCCH=CHCOO]•2H O, CoMal). The polymerꢀ
2
C, 58.6; H, 3.2; N, 12.5. According to the gravimetric analysis,
the metalꢀcontaining component accounts for 39.6 wt %, while
the matrix is 60.4 wt. %. The kinetics of the isothermal transforꢀ
mations of metalꢀcontaining monomers (MCM) was studied
based on gas evolution using a membrane zero manometer. Therꢀ
molysis was carried out under static isothermal conditions at
temperatures Teхp in selfꢀgenerated atmosphere (the samples
were preꢀevacuated at room temperature for 30 min) under dyꢀ
namic vacuum conditions and under argon. The gaseous and
condensed products of the thermal transformation were studied
by IR spectroscopy in the 400—4000 cm– range (Specord 75 IR
spectrophotometer) and analyzed by mass spectrometry using an
MSꢀ3701 quadrupole mass spectrometer.
Powder Xꢀray diffraction analysis was carried out on DRON
UMꢀ2 and Philips PW 1050 diffractometers using CuꢀKα radiaꢀ
tion (λ = 1.5418 Å). Magnetic measurements of metal—polymer
nanocomposites were performed by means of an Oxford Instruꢀ
ments Vibrating Sample Magnetometer (VSM). The hysteresis
loops were recorded in the temperature range of 5—300 K. The
temperature dependences of the magnetization were measured
in the same temperature range in low fields (2•10–3 T) using
field cooling (FC) and zeroꢀfield cooling (ZFC) modes and at
ization is accompanied by changes in the IR absorption
spectra of the dehydrated monomer, in particular, a deꢀ
crease in the intensity of the C=C stretching band and
convergence of the C=O stretching frequencies, giving
rise to one broadened absorption band at 1540—1560 cm .
When Texp > 523 K, thermally polymerized samples underꢀ
go intense gas evolution. The gas evolution rate W = dη/dt
decreases monotonically with an increase of the degree of
–
1
conversion η = Δα∑,t/Δα∑,f, where Δα∑,t = α∑,t – α∑,0
,
1
Δα∑,f = α∑,f – α∑,0, α∑,f, α∑,t, and α∑,0 are the final, curꢀ
rent, and the initial numbers of moles of gas products,
respectively, evolved per mole of the starting sample at
room temperature. The gas evolution kinetics η(τ) is satisꢀ
factorily approximated in the general form (up to η ≤ 0.95)
by the equation for two parallel reactions:9
η(τ) = η [1 – exp(–k τ)] + (1 – η )[1 – exp(–k τ)], (1)
1f
1
1f
2
where τ = t – t (t is the sample heating time, η =
1f
0
0
= η(τ)⏐
→∞, k and k are the effective rate conꢀ
k t 0, k1t 1 2
→
2
0
.6 T and 5—300 K. The electron microscopic examinations of
stants for the reactions. The parameters k , k , η and
1 2 1f
metalꢀcontaining nanocomposites were performed using a Hitaꢀ
chi 3500 scanning electron microscope (15 kV), a JEOL transꢀ
mission electron microscope with accelerating voltage of 100 kV,
and JEM 3010 highꢀresolution electron microscope (300 kV).
The particle geometric size distribution was determined from
a sample of 50—100 measurements using photomicrographs.
Δα∑,f depend on the temperature of the thermolysis (Tterm):
η , Δα = Аexp[–Ea,eff/(RT)],
∑, f
(2)
(3)
1f
keff = k0,effexp[–Ea,eff/(RT)],
where А and k0,eff are preꢀexponential factors, Ea,eff is the
effective activation energy.
Results and Discussion
The initial gas evolution rate Wτ = 0 = W is
0
Preparation, composition, and microstructure of magꢀ
netically active nanocomposites. A study of the kinetics
and mechanisms of thermal transformations of МCМ
showed that their thermolysis is a multistage process that
includes three key macro stages: dehydration, polymerꢀ
ization of the dehydrated monomer, and decarboxylation
W = η k + (1 – η )k .
(4)
0
1f
1
1f
2
Equations (1) and (4) describe the gas evolution kinetics
of NiAcr and coꢀcrystallized FeCoAcr, Fe CoAcr, and
2
2
Fe NiAcr (Table 1).
2

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478
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
Pomogailo et al.
Table 1. Kinetic parameters of gas evolution during thermolysis of unsaturated metal carboxylates
Sample
Element analysis data of
W = k0,effexp[–Ea,eff/(RTterm)]
0
the thermolysis products, wt. %
k0,eff/s–1
Ea,eff
kJ mol–
1
/
С
Н
Metalꢀcontaining
component
1
4
1
CoAcr2
26.6
29.6
1.1
1.9
86.8
67.1
3.0•10
238.3
246.5
Fe OAcr6
4.2•102
3
(
473—573 K)
Fe OAcr6
29.6
1.9
67.1
1.3•106
127.5
3
(
573—643 K)
1
7
2
2
4
NiAcr2
FeСоAcr
Fe СоAcr
Fe NiAcr
27.6
—
33.4
—
1.1
—
3.3
—
83.7
—
—
—
—
4.4•10
1.3•10
1.1•10
2.7•10
247.0
207.0
205.0
205.0
125.4
1
1
2
1
2
6
CoMal
—
—
1.1•10
When k ≈ 0, η1f → 1
from the aboveꢀlisted gaseous products, CH was found in
2
4
the case of CoAcr (trace amount) and NiAcr (amount
2
2
η(τ) ≈ 1 – exp(–k τ),
(5)
(6)
1
comparable with CO ). Electron microscopic examinaꢀ
2
tion of the final products of МCМ thermolysis showed
morphologically similar images, namely, electronꢀdense
particles distributed in a less electronꢀdense matrix. The
particles are nearly spherical, they have a narrow size disꢀ
tribution, and occur as both single structures and aggreꢀ
gates (Fig. 2). According to transmission electron microꢀ
W ≈ k .
0
1
Equations (5) and (6) describe the gas evolution kinetꢀ
ics during thermal transformations of Co acrylate and
maleate (Fig. 1).
Composition of gaseous and solid products of thermolyꢀ
sis of МCМ. The major gaseous product formed in the
transformations of the metal acrylates and maleates and
their coꢀcrystallizates is CO . This was confirmed by
IR spectroscopy and mass spectrometry. Carbon monꢀ
oxide, hydrogen, and H O, H C=CHCOOH, and
HOCOCH=CHCOOH vapors, which condense at room
temperature, are formed in much smaller amount. Apart
II
III
scopy data for the nanocomposite based on Fe acrylate
obtained at 663 K (degree of conversion of 55.5%), two
fractions of particles with average sizes of 12.3 and 22.1 nm
are present. The average size of nanocrystallites calculated
by the Scherrer equation is 13.5 nm. According to Xꢀray
2
2
2
II
diffraction data for the thermolysis product of Co acrylate,
the average particle size is 7 nm. The fraction of particles
of 6.7 nm size is ∼ 50%, the fractions of 12 and 21 nm
particles correspond to 27 and 14 %, respectively, and the
fraction of other particles is 8.4%. The major nanocrystalꢀ
line phase of the product is CoO, which is formed at 643 K
for a degree of conversion of 48.6%. Cobalt oxides or carꢀ
bides of nonꢀstoichiometric compositions are also formed
in minor amounts. It is noteworthy that the average size of
particles formed upon thermal transformations of unsatꢀ
urated metal carboxylates is below that observed for the
products of thermal transformations of saturated metal
carboxylates (see Fig. 2, e). Nanoꢀsized particles are locatꢀ
ed in the matrix rather uniformly, the average distance
between the particle centers being 8—10 nm. The Xꢀray
diffraction patterns of some obtained nanocomposites are
presented in Fig. 3.
η
1
2
3
4
5
1
0
0
0
0
.0
.8
.6
.4
.2
2
00
400 t/min
b
–
–
0.5
a
1.0
lg(1 – η)
1
00 200
300
400
500 600
t/min
Magnetic properties of cobaltꢀcontaining nanocomposꢀ
ites. The magnetic characteristics of cobalt nanoparticles
are known to be tightly connected with their structure,
Fig. 1. Gas evolution kinetics η(t) (a) and semilogarithmic lines
log(1 – η) vs. t) (b) for the thermolysis of Co maleate (CoMal)
in selfꢀgenerated atmosphere at 653 (1), 643 (2), 633 (3), 623 (4),
and 613 K (5).
II
(
1
4
especially in core—shell structures. As shown previousꢀ
1
5
ly, the nature of the unsaturated МCМ ligand can conꢀ

Reactivity of metalꢀcontaining monomers
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1479
a
c
5
0 nm
100 nm
b
50 nm
N /ΣN (%)
d
d
d
5
4
3
2
1
0
a´
b´
0
0
0
0
1
0 nm
5
0 nm
7
12 20 27 35 42 54 62 d/nm
N /ΣN (%)
d
d
3
2
1
2
1
0
0
8
16
24
32
40 d/nm
Fig. 2. Microstructure of the products of thermolysis (T = 773 K) of acrylamide CoII (a,a´) and FeIII (b,b´) complexes, Co acrylate
II
II
(
643 K) (c) and size distribution of the metalꢀcontaining particles in the nanocomposites based on them: (d) Co acrylate; (e) FeIII
II
acrylate (1), Fe(HCOO) •2H O (2), Co maleate (3).
2
2
siderably affect the phase composition and the structure of
the thermolysis products being formed. Therefore, it was
of interest to compare the magnetic properties of the prodꢀ
ucts of thermolysis of various monomeric precursors,
4.48 emu g–1m while at 5 K, this value is 1.98 emu g–1
Note that the latter value is much higher than that
.
1
6
measured in the same fields for 560 nm CoO particles
–
1
(0.02 emu g ). Moreover, the M(T) curve shows no tranꢀ
sition corresponding to the Neel temperature for CoO
(TN = 293 K), indicating additional ferri/ferromagnetic
phases with a Curie point above the room temperature. The
coercive force decreases from 0.0814 T at 5 K to 0.031 T at
300 K and has a characteristic maximum at ∼ 25 K. The resiꢀ
II
the Co acrylate (CoAcr ) and acrylamide (CoAAm)
2
complexes.
The dependences of the magnetization of the CoAcr2
thermolysis product (Texp = 643 K) on the magnetic field
strength at 5 and 300 K at about ±1.1 T (916.6 kA m–1) are
shown in Fig. 4. As the temperature decreases, the hysterꢀ
esis loop is broadened, and highꢀfield magnetization inꢀ
creases. The coercive force is 0.08 and 0.03 T for temperaꢀ
tures of 5 and 300 K, respectively. The hysteresis loop at
dual magnetization (M ) is 2.325 (5 K) and 0.816 mT (300 K).
r
In ZFC measurements, a monotonic increase with
temperature rise was observed, the broad gap between the
FC and ZFC curves being indicative of the presence of
fairly strong interactions between the particles; the negaꢀ
tive ZFCꢀmagnetization values are apparently caused by
the effect of the diamagnetic organic matrix. Cobalt nanoꢀ
particles with a metal core and oxide CoO shell demonꢀ
3
00 K corresponds to the typical behavior of a material
with preferable ferromagnetic order. At low temperature,
the pattern of the magnetization curve considerably changꢀ
es, and the susceptibility (dM/dH) in high fields increases
almost 5ꢀfold, indicating a considerable contribution of
the antiferromagnetic CoO phase.
1
7,18
strate soꢀcalled exchange anisotropy phenomenon,
which is caused by exchange interaction at the boundary
of two different ferroꢀ and antiferromagnetically ordered
systems. The exchange anisotropy is phenomenologically
At room temperature, the product of CoAcr thermolꢀ
2
ysis (Texp = 643 K) has a saturation magnetization of

1
480
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
a
Pomogailo et al.
I
I
b
(111)
(111)
(
200)
(
200)
(
220)
(220)
(311)
(311)
4
0
50
60
70
80
90 2θ/deg
40
50
60
70
80
90
2θ/deg
I
I
c
d
(110)
(031)
(102)
(211)
(201)
(112)
(210)
(221)
(211)
(301)
(123)
(303)
332)
(
(
200)
(430)
(
220)
4
0
50
60
70
80
90 2θ/deg
40
50
60
70
80
90
2θ/deg
I
e
f
I
(111)
(111)
(
200)
(
200)
(
220)
(
220)
(311)
(311)
4
0
50
60
70
80
90
2θ/deg
40
50
60
70
80
90 2θ/deg
Fig. 3. XꢀRay diffraction patterns for the products of thermolysis of the acrylamide complexes formed at different thermolysis
temperatures: CoAAm at 873 (a) at 1073 K (b), FeAAm at 773 (c) and 873 K (d), NiAAm at 773 (e) and 873 K (f).
manifested as the difference of the hysteresis curves obꢀ
tained upon FC and ZFC measurements. As can be seen
in Fig. 4, the ZFC hysteresis curve for the product of
ate and acetylenedicarboxylate) show a ferromagnetic beꢀ
havior at room temperature, and the hysteresis loops meaꢀ
sured at 5 K in the FC mode with applied magnetic field
strength of 5 T are also typical of systems with exchange
CoAcr thermolysis is symmetric relative to the origin of
2
II
coordinates, whereas the FC curve is nonꢀsymmetric
anisotropy. For the products of thermolysis of Co acetyꢀ
(
shifted to negative fields), i.e., exchange interaction beꢀ
lenedicarboxylate and itaconate, the exchange bias field
tween the ferromagnetically ordered core spins and the
antiferromagnetically ordered shell spins arises at the core/
shell interface. Note that the products of thermal transforꢀ
(H ) and the coercive force were H = 1.8 and 1.3 Oe,
eb
eb
H = 2.5 and = 2.0 kOe, respectively.
c
Unlike the products of thermolysis of carboxylate type
МCМ, nanocomposites based on acrylamide complexes
II
mations of unsaturated metal dicarboxylates (Co itaconꢀ

Reactivity of metalꢀcontaining monomers
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1481
μ0H/T
a
M/emu g–1
b
5
2
.0
5
5
К
FC
.5
3
ZFC
3
00 К
ZFC
M/emu g–1
–1.2
–0.8
–0.4
0.4
0.8
M/emu g
2
μ H/T
0
–
1.2
–0.4
0.4
–
1
FC
–
–
3
5
–
–
2.5
5.0
–
0.2
0
0.2 μ H/T
0
–
2
Fig. 4. Magnetization vs. magnetic field strength (a) and FC and ZFC hysteresis loops (b) measured at 5 K in a 1.1 T field for the
CoAcr thermolysis product.
2
contain highly dispersed metal phase or, at higher temperꢀ
atures of thermolysis, metal carbide phase. For example,
atures of thermolysis demonstrated that H , M , and M
c s r
increase as the temperature of thermolysis increases. The
in the products of thermolysis of CoAAm at Texp
673—873 K, the metal phase is βꢀCo with the lattice
parameter α = 3.54470 Å and at 1073 K, this is CoC
=
highest H value is observed for the product of thermolysis
c
=
at 1073 K with a nanocrystallite size of 10—18 nm. As the
particle size increases, the effective anisotropy of nanoꢀ
crystals is enhanced, resulting in a decrease in the role of
thermal fluctuations.
1
x
1
5
(
α2 = 3.61265 Å). Therefore, it was of interest to track
the magnetic properties of the products of thermal transꢀ
formations of CoAAm obtained at temperatures of 673,
Magnetic properties of ironꢀcontaining nanocomposites.
According to powder Xꢀray diffraction, the solid product
7
73, 873, and 1073 K. The hysteresis loops measured in
III
the temperature range of 90—300 K attest to the ferroꢀ
magnetic behavior of the thermolysis products (Fig. 5).
However, the pattern of the curves, especially in the case
of thermolysis product formed at 673 K, indicate the probꢀ
able presence of a disordered interfacial layer with a skewed
spin structure on the surface of magnetic particles. The
sample does not show clearꢀcut superparamagnetic beꢀ
havior at room temperature, although the average size
of nanocrystallites is 7 nm, i.e., they are smaller than
the critical size needed for the superparamagnetism to be
manifested.
of transformation of Fe acrylate at the thermolysis temꢀ
perature Texp = 663 K is highly dispersed nanocrystalline
magnetite with a 13 nm average size of particles homoꢀ
geneously dispersed in the matrix. The magnetization
curves of a sample of this product measured at 5 and 300 K
in a ±1.1 T range are shown in Fig. 6. The hysteresis loops
are symmetric relative to the origin of coordinates and
closed. The coercive forces are 0.008 T and 2.73 mT for
temperatures of 5 and 300 K, respectively. As the temperꢀ
ature is raised from 5 to 300 K, the saturation magnetizaꢀ
–
1
tion varies from 25.66 to 21.82 emu g . Note for comparꢀ
The coercive force and the residual magnetization deꢀ
crease as the temperature increases. For example, for the
ison that the corresponding values for the "bulk" magneꢀ
tite obtained in the same fields are 98 and 92 emu g–
.
1 19
product of CoAAm thermolysis at 673 K, the H value
The decrease in the magnetization is likely to be due to the
antiferromagnetic spin structure of the surface atoms of
the nanoparticles. The magnetization dependences on the
temperature measured in the FC and ZFC modes in
a 0.005 T field are shown in Fig. 7. As in the case of
Co systems, the shape of the curves attests to strong interꢀ
particle interactions.
c
–
1
–1
changes from 0.068 T (68 kA m ) to 0.005 T (5 kA m
)
–
1
and M varies from 13.6 to 2.2 emu g as the temperature
r
is raised from 5 to 300 K. The saturation magnetization
changes little with temperature. Similar trends are also
characteristic of other products.
The magnetization in the FC measurements almost
does not depend on the temperature; in the case of ZFC
measurements, the magnetization increases with temperꢀ
ature rise; however, no maximum corresponding to the
blocking temperature is present.
The hysteresis loops for the product of thermolysis of
III
the acrylamide complex of Fe nitrate at 873 K were
recorded at 5 and 300 K (Fig. 8). The shape and the patꢀ
tern of the curves correspond to a ferromagnetic material.
–
1
Comparative analysis of the magnetic characteristics
of CoAAm nanocomposites obtained at different temperꢀ
The saturation magnetization is 40 emu g at room temꢀ
perature. The hysteresis loop at 300 K has a minor inflecꢀ

1482
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
Pomogailo et al.
H/kA m–1
H/kA m–1
a
b
3
0
2
1
0
0
1
0
–
1600
–600
0 К
0
400 900 1400 1900 M/emu g–1 –1600
H/kA m–1
–600
0
400 900 1400 1900 M/emu g–1
–1
H/kA m
9
9
0 К
300 К
8
5
3
00 К
0 К
–
–
–
–
–
20
30
40
50
60
9
0 К
–
30
9
–
50
0
50
M/emu g
–
40
0
40
–50
70
–1
M/emu g–
1
3
00 К
–
8
–
300 К
–
5
H/kA m–1
H/kA m–1
c
d
5
3
0
0
2
5
5
0
400 900 1400 1900 M/emu g–1
–
1600
–600
400 900 1400 1900 –M/emu g–1 –1600
H/kA m 1
00 К
–600
90 К
0
–1
3
H/kA m
2
0
300 К
0 К
20
9
0 К
9
9
0 К
–50
–
–
–
35
55
75
–
70
–
50
50
–50
0
50
M/emu g
M/emu g–
1
–1
–90
3
00 К
300 К
–
20
–20
Fig. 5. Magnetization vs. magnetic field in the temperature 90—300 K for the CoAAm thermolysis products formed at 673 (a), 773 (b),
73 (c), and 1073 K (d).
8
tion, indicating the presence of two phases with different
coercive forces. This fact is consistent with the Mössbauer
spectroscopy data and confirms that the product of therꢀ
molysis of the iron acrylamide complex comprises two
ferromagnetic phases, Fe C and αꢀFe (Table 2). The specꢀ
3
trum of the thermolysis product exhibits two sextets, indiꢀ
cating the formation of a ferromagnetic phase: Fe C acꢀ
3
counts for 86.87%, αꢀFe makes 3.17%, and the rest are
paramagnetic phases.
M/emu g–1
2
2
1
8
1
4
7
5
К
Table 2. Mössbauer spectroscopy data for the acrylamide comꢀ
plex of Fe nitrate and products of polymerization and therꢀ
molysis at 873 K
III
3
00 К
Sample
IS
QS
Hhf
Phase
Content
/
T
composition (wt. %)
mm s–1
–
1.2
–0.8
–0.4
0.4
0.8
μ0H/T
Monomer
0.270 0.650
.340 1.413
0.270 0.650
.340 1.413
Thermolysis 0.070 0.000
0.0
0.0
0.0
PPI
PPII
PPI
85.70
14.30
66.63
33.37
86.87
3.170
–
7
0
Polymer
–
–
–
14
21
28
0
0.0
PPII
20.7
32.8
0.0
Fe C
3
product
0.073 0.000
0.840
αꢀFe
PPI, PPII Residue
Fig. 6. Magnetization vs. magnetic field at temperatures of 5 and
Note. IS is isomer shift, QS is quadrupole splitting, Hhf is hyperꢀ
fine field, PPI and PPII is paramagnetic phase.
III
3
00 K for the Fe acrylate thermolysis product at ±1.1 T.

Reactivity of metalꢀcontaining monomers
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1483
M/emu g–1
μ0H/T
a
2.0
1.5
1.0
0.5
60
FC
4
0
5
К
3
00 К
1.0 M/emu g–1
ZFC
–
1.2
–1.0
–0.5
0.5
–
–
40
60
Fig. 8. Hysteresis loops measured at 5 and 300 K in a ±1.1 T field
III
for the thermolysis product of the Fe nitrate acrylamide comꢀ
plex at 873 K.
5
0
100
150
200
250 300 T/К
M/emu g–1
b
M/emu g–1
2
2
1
8
1
4
3
0
3
00 К
FC
5 К
75 К
2
0
ZFC
0.4
7
10
0
–
1.2
–0.8
–0.4
0.8 μ0H/T
–
1.5
–1.0
–0.5
0.5
1.0
μ0H/T
–
7
M/emu g–1
2
0
–10
FC
–
–
–
14
21
28
ZFC
–
20
–0.3
0.3
μ0H/T
–
20
–30
Fig. 7. Magnetization vs. temperature in the FC and ZFC modes
in a 0.005 T field (a) and FC and ZFC hysteresis loops (b) meaꢀ
sured at 5 K in a ±1.1 T field for the Fe acrylate thermolysis
Fig. 9. Magnetization vs. field curves at temperatures of 5, 75,
and 300 K for the thermolysis product of the coꢀcrystallized
III
III
II
Fe and Co acrylates (Texp = 643 K).
product.
variation of the residual magnetization and M with temꢀ
s
The coercive force decreases from 0.27 to 0.06 T as the
temperature increases from 5 to 300 K. The pattern of
perature implies a certain contribution of the temperaꢀ
tureꢀdependent magnetocrystalline anisotropy of Fe C to
3
Table 3. Measurement of the magnetic characteristics of the solid phase during the thermal transformation of NiII
acrylate (Texp = 643 K)
3
–1
3
–1
5
3 –1
Δm/m0
мас.%)
σ /G cm g
σ /G cm g
χ •10 /G cm g
ηF
s
F
σ
(
3
00 K
77 K
300 K
77 K
300 K
77 K
300 K
77 K
0
1
2
3
4
5
0.209
0.235
0.323
0—
0.930
14.360
0—
0.000
0.024
0.084
0—
0.624
12.800
0—
2.55
2.19
2.53
0—
3.24
16.70
0—
0
0
–
4
–4
9.1
7.1
5.4
6.0
1.2
0.675
1.447
2.177
2.184
14.950
0.041
0.155
1.240
1.949
13.780
6.70
11.80
9.90
11.60
12/3
4.4•10
7.5•10
2.84•10
2.28•10
1.74•10
0.235
1.54•10–3
0—
–3
–
2
1.14•10–2
0.235
–2
Note. σ = σ (9446 Oe) is the magnetization in a 9446 σ field; σ → σ(0) is extrapolation of the magnetization to zero field;
s
F
χσ = χ (9446 Oe) is the specific magnetic susceptibility in a 9446 Oe field; ηF = σ / σ (Ni) is the weight fraction of the
F
s
Ni metal phase in the sample under the assumption that the ferromagnetism is wholly due to this phase, M (Ni) =
s
3
–1
=
54.5 G cm g .

1484
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
Pomogailo et al.
the overall magnetic behavior. The FC curves measured in
.002 and 0.6 T fields show some deviations at low temꢀ
lized cobalt(II) and iron(III) acrylate. The solid products of
thermal transformations of coꢀcrystallized Co and Fe
II
III
0
peratures (at 5 K) similarly to the M (T) dependence. This
acrylates with a Fe : Co atomic ratio of 2 : 1 (Fe CoAcr)
r
2
may be related to irreversible magnetization processes at
low temperature caused, as discussed above, by the nonꢀ
collinearity of the spins of surface atoms.
Characteristic features of the magnetic properties of
nanocomposites obtained by thermolysis of the coꢀcrystalꢀ
have a nonꢀuniform phase composition (CoFe O , Fe O ,
2
4
3
4
CoO) of the nanocrystalline particles characterized by
rather narrow size distribution (average size 12 nm) in the
formed matrix space. The nanoparticle composition and
structure are also reflected in the complex character of the
sample magnetic properties. Thus hysteresis loops below
200 K are open and shifted toward negative magnetic field
a
H/kA m–1
(
Fig. 9). This can be attributed to strong irreversible magꢀ
netic processes. An additional contribution of the effects
related to "freezing" of the disordered surface spins of the
nanoparticles occurring under close interaction with the
2
–
1100 –600
0
400 900 1400 M/emu g–1
H/kA m–1
matrix carbon molecules cannot be ruled out either.
20
0
.2
–
4
M/emu g–1
a
0
.1
2
.5
2.0
1.5
–
–
6
8
–
10–8 4
4 6 8 10
M/emu g–1
0.1
.2
FC
0
1
.0
H/kA m–1
b
ZFC
1
0
5
0.5
1
00
200
300
T/К
–
1100 –600
0
400 900 1400
H/kA m–1
.5
M/emu g–1
M/emu g–1
b
6
1
FC
5
–
10
4
3
–
–
15
20
–
10
10
M/emu g–
1
ZFC
2
1
–
1.5
H/kA m–1
c
1
00
200
300
T/К
1
0
M/emu g–1
c
4
–
1100 –600
0
400 900 1400
M/emu g–1
FC
H/kA m–1
6
3
2
1
–
–
–
20
30
40
ZFC
–
30
30
M/emu g–
1
1
00
200
300
T/К
–
6
Fig. 10. Magnetization vs. magnetic field curves measured in the
Fig. 11. Magnetization vs. temperature in the FC and ZFC modes
in a 8 kA m– field (0.008 T) for the products of thermolysis of
1
temperature range of 90—300 K for the products of thermolysis
II
II
of the acrylamide complex of Ni nitrate formed at temperaꢀ
the acrylamide complex of Ni nitrate formed at temperatures
tures of 673 (a), 773 (b), and 873 (c).
of 673 (a), 773 (b), and 873 K (c).

Reactivity of metalꢀcontaining monomers
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1485
In the temperature range of 200—300 K, the coerꢀ
pattern of their change is illustrated by the data presented
in Table 3.
cive force H and residual magnetization decrease and at
c
room temperature they are 0.035 T and 7.49 mT, resꢀ
pectively.
The observed nonmonotonic dependence of σ and σF
s
on the time of thermolysis (degree of weight loss by the
sample) is probably due to the sharp increase in the rate of
formation of the ferromagnetic phase at the end of transꢀ
formation and indicates that the metalꢀcontaining prodꢀ
ucts formed during the transformation occur for a long
period in a weakly magnetic phase. At the final stages of
thermolysis, ηF ≈ 0.23—0.25, i.e., only ∼ 25% of the Ni
atoms occur in the ferromagnetic phase, while the other
Ni atoms occur in the weakly magnetic phase. The final
transformation product has the following magnetic charꢀ
Magnetic properties of nickelꢀcontaining nanocomposꢀ
ites. For more detailed investigation of the magnetic phase
formation during the thermal transformations of metalꢀ
containing monomers, the dependence of the magnetic
characteristics on the reaction time was studied in relation
II
to the products of thermolysis of Ni acrylate with various
II
weight losses. The magnetization of the starting Ni
3
–1
acrylate (NiAcr ) is σ (300 K) = 0.209 G cm g and
2
s
the specific magnetic susceptibility is χ (300 K) =
σ
4
3 –1
=
0.255•10– cm g . The magnetic moment for NiAcr2
acteristics: M (300 K) = 14.36 (300 K), 14.95 (77 K)
s
3
–1
5
3 –1
is μeff = 3.40 μ ; this is close to the purely spin value
G cm g ; χ •10 = 16.7 (300 K), 12.3 (77 K) cm g ;
σ
B
μ = 2.83 μ , which is typical of the octahedral symmetry
H = 8.94 (300 K), 53.6 (77 K) Oe; j = 0.02 (300 K),
s
B
с
r
2
+
of Ni . During the thermolysis, σ and χ change. The
0.133 (77 K), where j is the squareness ratio.
s
σ
r
1
00 nm
50 nm
3
0 nm
10 nm
Fig. 12. Photomicrographs of the product of thermolysis of acrylamide complex of NiII nitrate formed at 673 K.

1
486
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
Pomogailo et al.
The Niꢀcontaining nanocomposites obtained during
the thermal transformations of the acrylamide complex
Co(CH =CHCONH ) (H O) ](NO ) (NiAAm), have
higher dispersity of the metal phase and more homogeꢀ
neous distribution in the matrix space (the experimental
data that substantiate this conclusion are not given in the
paper) than the Coꢀ and Feꢀcontaining nanocomposites,
especially at lower thermolysis temperatures. It could be
expected that in these systems, the assembly of Ni nanoꢀ
particles would show superparamagnetic behavior.
presented in Fig. 10. The hysteresis loops for the products
obtained at 673 and 773 K attest to the formation of suꢀ
perparamagnetic particles, whereas the product of therꢀ
molysis at 873 K shows a ferromagnetic behavior, which is
also supported by the thermomagnetic characteristics of
the Ni nanoparticle assembly in the systems in question
(Fig. 11). It can be seen that an inflection corresponding
to the blocking temperature appears in the ZFC curves:
the product obtained at 673 K at T > T (T ≈ 40 K is the
[
2
2 4
2
2
3 2
b
b
characteristic blocking temperature for magnetic nanoꢀ
particles) is a superpramagnetic material. According to the
measurements, magnetization of an assembly in a strong
The dependences of the magnetization of the obtained
Niꢀcontaining nanocomposites on the applied magnetic
field strength in the temperature range of 90—300 K are
–
1
magnetic field at T < T is ∼ 3 emu g ; with allowance
b
–
3
made for the saturation magnetization M = 500 emu g
s
–
3
and the nickel density ρ = 8.9 g cm , this corresponds to
the magnetization of an assembly of nickel particles with an
average diameter d = 7 nm located at distances d ≈ 20 nm.
This conclusion is in satisfactory agreement with the elecꢀ
tron microscopy data (Fig. 12). The experimental value of
–
1
H /kA m
a
c
1
1
6
2
8
4
the blocking temperature T = 40 K can be explained by
b
the presence of nickel particles with greater diameters
(d = 14—16 nm) or by the effect of the surface anisotropy
of particles.
The temperature dependences of H indicate the deꢀ
c
crease in the coercive force for the thermolysis product at
–
1
7
3
73 K from 0.0077 T (7.7 kA m ) at 90 K to nearly zero at
7
00
750
800
850
Texp/К
00 K. The M and M values for all products differ little
s
r
–
1
with temperature.
M /emu g
s
b
An increase in the thermolysis temperature results in
an increase in the particle size of Niꢀcontaining nanoꢀ
composites from 6—7 nm (673 K) to 8—14 nm (773 K)
and 12—17 nm (873 K). The key magnetic characteristics
of these products at room temperature are also consistent
with different types of their magnetic behavior (Fig. 13).
3
2
1
0
0
0
The sharp increase in H for the product obtained at 873 K
c
indicates that at this temperature, the material switches
from superparamagnet to ferromagnet.
Thus, the advantage of the polymerization—destrucꢀ
tion synthesis of metal nanoparticles is not only the
fact that this provides stabilized magnetic nanoꢀ
particles resistant to oxidation and aggregation; this apꢀ
proach also allows for the effective control of nanoparticle
size and, finally, magnetic properties. Indeed, the nanoꢀ
composites based on acrylamide metal complexes, unlike
those formed from carboxylate precursors, are characꢀ
terized by higher dispersity and contain metal nanoꢀ
particles, and only at high synthesis temperatures, carꢀ
bide phases appear. The metalꢀcontaining nanocomposꢀ
ites are magnetic materials with ferroꢀ and superparamagꢀ
netic properties.
7
00
750
800
850
Texp/К
–
1
c
M /emu g
r
6
4
2
7
00
750
800
850
Texp/К
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 11ꢀ03ꢀ00769)
and the Presidium of the Russian Academy of Sciences
(Fundamental Research Program No. 21 "Foundation of
Fig. 13. Coercive force H (a), saturation magnetization (M ),
and residual magnetization (M ) of the product of thermolysis of
acrylamide complex of Ni nitrate vs. thermolysis temperature.
c
s
r
II

Reactivity of metalꢀcontaining monomers
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1487
Fundamental Research of Nanotechnologies and Nanoꢀ
materials").
11. E. I. Aleksandrova, G. I. Dzhardimalieva, A. S. Rozenberg,
A. D. Pomogailo, Izv. Akad. Nauk, Ser. Khim., 1993, 303;
3
2
08; 1743 [Russ. Chem. Bull. (Engl. Transl.), 1993, 42, 259;
64; 1666].
References
1
2. G. I. Dzhardimalieva, Doctoral Thesis (Chem.), Institute of
Problems of Chemical Physics, Russ. Acad. Sci., Cherꢀ
nogolovka, 2009, 399 pp. (in Russian).
1
. G. I. Dzhardimalieva, A. D. Pomogailo, N. D. Golubeva,
S. I. Pomogailo, O. S. Roshchupkina, G. F. Novikov, A. S.
Rozenberg, M. Leonowicz, Kolloid. Zh., 2011, 73, 457 [Colꢀ
loid. J. (Engl. Transl.), 2011, 73, 458].
13. A. D. Pomogailo, A. S. Rozenberg, G. I. Dzhardimalieva,
Usp. Khim., 2011, 80, 272 [Russ. Chem. Rev. (Engl. Transl.),
2011, 80, 257].
2
3
. S. P. Gubin, Yu. A. Koksharov, G. B. Khomutov, G. Yu.
Yurkov, Usp. Khim., 2005, 74, 539 [Russ. Chem. Rev.
14. G. Yu. Yurkov, D. A. Baranov, A. V. Kozinkin, Yu. A. Kokꢀ
sharov, T. I. Nedoseikina, O. V. Shvachko, S. A. Moksin,
S. P. Gubin, Neorgan. Mater., 2006, 42, 1112 [Inorg. Mater.
(Engl. Transl.), 2006, 42, 1012].
15. E. Sowka, M. Leonowicz, B. Andrzejewski, A. D. Pomoꢀ
gailo, G. I. Dzhardimalieva, J. Alloys Comp., 2006, 423, 123.
16. L. Zhang, D. Xue, J. Mater. Sci. Lett., 2002, 21, 1931.
17. A. E. Berkowitz, K. Takaro, J. Magn. Magn. Mater., 1999,
200, 552.
(
Engl. Transl.), 2005, 74].
. D. J. Sellmyer, M. Yu, R. D. Kirby, Nanostruct. Mater.,
999, 12, 1021.
1
4
5
. I. Safarik, M. Safarikova, Monatsh. Chem., 2002, 133, 737.
. S. Mornet, S. Vasseur, F. Grasset, E. Duguet, J. Mater.
Chem., 2004, 14, 2161.
. Q. A. Pankhurst, J. Connolly, S. K. Jones, J. Dobson, J. Phys.
D: Appl. Phys., 2003, 36, R167.
. D. Craik, Magnetism: Principles and Applications, John Wiley
and Sons, Inc., New York, 1995.
. J. P. Jakubovics, Magnetism and Magnetic Materials, 2nd ed.,
The Institute of Materials, Cambridge, 1994.
6
7
8
9
18. M. Kiwi, J. Magn. Magn. Mater., 2001, 234, 584.
19. Z. Kakol, J. M. Honig, Phys. Rev. B, 1989, 40, 9090.
20. R. H. Kodama, J. Magn. Magn. Mater., 1999, 200, 359.
. A. D. Pomogailo, G. I. Dzhardimalieva, A. S. Rozenberg,
D. N. Muraviev, J. Nanoparticle Res., 2003, 5, 497.
1
0. A. D. Pomogailo, G. I. Dzhardimalieva, Vysokomolekulyar.
Soedineniya, Ser. A, 2004, 46, 437 [Polym. Sci., Ser. A
Received March 4, 2011;
(
Engl. Transl.), 2004, 46, 250].
in revised form June 21, 2011