Structure and magnetic properties of polymer matrix nanocomposite processed by pyrolysis of cobalt(II) acrylate

Article abstract of DOI:10.1016/j.jallcom.2003.09.042

Structure and magnetic properties of the nanocomposite, processed by a pyrolysis of cobalt(II), acrylate were investigated. The X-ray and transmission electron microscopy (TEM) studies revealed that the product of thermal decomposition of the initial acrylate consisted of antifferromagnetic CoO nanocrystals as well as others crystalline phases, embedded in a polymer matrix. The temperature dependence of the magnetisation and the magnetisation curves indicate that these additional phases exhibit ferro-/ferri-magnetic ordering with the Curie point above room temperature.

Full text of DOI:10.1016/j.jallcom.2003.09.042

Journal of Alloys and Compounds 369 (2004) 244–246
Structure and magnetic properties of polymer matrix nanocomposite
processed by pyrolysis of cobalt(II) acrylate
a
b
b
a,∗
´
M. Ławecka , A. Slawska-Waniewska , K. Racka , M. Leonowicz ,
c
c
c
I. Dzhardimalieva , A.S. Rozenberg , A.D. Pomogailo
a
Faculty of Materials Science and Engineering, Warsaw University of Technology, Warsaw, Poland
b
Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
c
Institute of Problem of Chemical Physics, Russian Academy of Sciences, 142432, Chernogolovka, Moscow Region, Russia
Abstract
Structure and magnetic properties of the nanocomposite, processed by a pyrolysis of cobalt(II), acrylate were investigated. The X-ray
and transmission electron microscopy (TEM) studies revealed that the product of thermal decomposition of the initial acrylate consisted of
antifferromagnetic CoO nanocrystals as well as others crystalline phases, embedded in a polymer matrix. The temperature dependence of the
magnetisation and the magnetisation curves indicate that these additional phases exhibit ferro-/ferri-magnetic ordering with the Curie point
above room temperature.
©
2003 Elsevier B.V. All rights reserved.
Keywords: Nanostructures; Magnetic measurements
1
. Introduction
2. Experimental
Thermal transformation of cobalt(II) acrylate, with the
The cobalt(II) acrylate complex Co(CH2=CHCOO)2·H2O
was prepared in a reaction of acrylic acid with suspension
of 2CoCO3·3Co(OH)2·H2O [1]. The complex was subse-
quently subjected to the thermal decomposition at 643 K
with the mass loss ꢀm = 48%. X-ray phase analysis was
performed with the use of a Philips PW 1050 diffractome-
ter, radiation Cu K␣. Microstructure was studied using a
JEM 1200 EXII transmission electron microscopy (TEM),
with accelerating voltage 100 kV. The magnetic properties
were measured using an Oxford instruments vibrating sam-
ple magnetometer (VSM).
general formula Co(CH2=CHCOO)2·H2O, consists of the
following steps: dehydration of the complex (monomer),
solid state polymerisation of the initial monomer and de-
carboxylation of the metallocarboxylate groups, followed
by formation of the metal or its oxide(s) as ultradispersed
particles. The final composition depends on the process-
ing temperature and time [1]. The main crystalline phase,
which is formed in the final stage of the cobalt(II) acry-
late pyrolysis, is CoO. The CoO is an antiferromagnet and
its magnetic unit cell consists of two superlattices. The
magnetic moments of both superlattices compensate each
other and the net magnetic moment is zero. Bulk CoO
shows antiferromagnetic transition at the Néel tempera-
ture of 293 K [2]. For nanosized CoO particles decrease
of the Néel temperature below 293 K and weak ferro-
magnetic behaviour at low temperatures were reported
3. Results
The X-ray studies proved that the main crystalline phase
in the product of pyrolysis is CoO, however, small amount
of others, crystalline phases, which we assume to be
non-stoichiomertic cobalt oxides or carbides, are also ob-
served. The reflections on the X-ray pattern are inconsistent
with any known equilibrium oxides or carbides (see Fig. 1).
The mean crystallite size of CoO particles, measured using
Sherrer method, is 7 nm. The TEM studies confirmed these
[
3,4].
∗
Corresponding author. Tel.: +48-22-660-84-50;
fax: +48-22-660-85-14.
E-mail address: mkl@inmat.pw.edu.pl (M. Leonowicz).
0
925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2003.09.042

M. Ławecka et al. / Journal of Alloys and Compounds 369 (2004) 244–246
245
250
200
150
100
CoO
5
0
0
3
0
40
50
60
70
80
2
theta [deg.]
Fig. 1. Diffraction pattern of the nanocomposite processed at 663 K,
m = 48%.
Fig. 3. Magnetisation vs. temperature, in external field 1 T.
ꢀ
results, however, one can see that the spherical particles are
partly agglomerated (Fig. 2).
5 and 300 K in the field range ± 1.1 T, are shown in Fig. 4.
The loops are closed and symmetrical about the origin.
The coercivity values are 0.08 and 0.03 T for temperatures
5 and 300 K, respectively. It can be seen that hystere-
sis loop recorded at 300 K shows behaviour typical of a
material with preferential ferromagnetic ordering. At low
temperatures the shape of the magnetisation curves changes
considerably. The high field susceptibility (dM/dH), which
is a slope of the linear portion of the M = f(H) curve, in-
creases five times with decrease of the temperature from
300 to 5 K. Thus, at low temperatures, besides of the ferro-
magnetic contribution, a substantial contribution from the
antifferomagnetic CoO phase is observed.
The magnetisation versus temperature, in a field of
0.005 T, measured in ZFC and FC regime, is shown in
Fig. 5. Continuous increase of the MZFC with temperature
and the wide gap between MZFC and MFC curves indicate
the presence of strong interactions between agglomerated
particles. The drop of the ZFC magnetisation to negative
values we attribute to the influence of the diamagnetic
organic matrix.
The temperature dependence of the magnetisation M(T),
measured in a field of 1 T is shown in Fig. 3. The magnetisa-
tion decreases rapidly from 4.48 emu/g down to 1.98 emu/g
for temperatures of 5 and 300 K, respectively. The latter
value (1.98 emu/g) is much higher than 0.02 emu/g, which
has been reported for the 560 nm particles of the CoO in the
same field [3]. Moreover, the Néel temperature of the CoO
phase is not seen on the M(T) curve. These observations
point to the presence of an additional ferri-/ferro-magnetic
phase in the material with its Curie point above room tem-
perature. We suppose that the shape of the M(T) curve
results from the contribution of at least two phases: fer-
romagnetic and antiferromagnetic, as well as the wide
distribution of the particle sizes and their agglomeration.
The multi-phase nature of the sample studied is also con-
firmed by the hysteresis loop. Selected loops, obtained at
5
5
K
2
,5
0
3
00 K
-
1,2
-0,4
0,4
1,2
-
2,5
-
5
H [T]
Fig. 2. TEM microstructure and electron diffraction pattern of the
nanocomposite processed at 663 K, ꢀm = 48%.
Fig. 4. ZFC hysteresis loops, recorded at 5 and 300 K.

2
46
M. Ławecka et al. / Journal of Alloys and Compounds 369 (2004) 244–246
0,006
0,005
0,004
0,003
0,002
0,001
0,000
acrylate a composite material consisting of nanosize CoO
FC
particles and unidentified ferri-/ferro-magnetic crystalline
phase, embedded in polymer matrix, was produced. The
material exhibits soft magnetic properties with room tem-
perature coercivity 0.032 T. These properties are supposed
to result from the presence of partly agglomerated fer-
romagnetic particles in the sample. The influence of the
diamagnetic organic matrix on the magnetic properties has
also been found.
ZFC
-
-
0,001
0,002
Acknowledgements
0
50
100
150
200
250
300
T [K]
Financial support from the State Committee for Scientific
Research (grant 4 T08E 056 22) is gratefully acknowledged.
Fig. 5. The ZFC and FC curves vs. temperature, recorded at 0.005 T.
References
4
. Conclusions
[
[
[
1] G.I. Dzhardimalieva, E.I. Aleksandrova, A.D. Pomogailo, A.S. Rozen-
berg, Russ. Chem. Bull. 42 (1993) 259.
2] B.D. Cullity, Introduction to Magnetic Materials, Addison-Wesley,
London, 1972, p. 157.
3] L. Zhang, D. Xue, J. Mater. Sci. Lett. 21 (2002) 1931–1933.
We have already shown that it is possible to synthesise
ultradispersed particles and simultaneously chemically pas-
sivate them by the in situ formation of polymer matrix dur-
ing thermal decomposition of metal-containing monomers
[1]. As a result of thermal decomposition of the cobalt(II)
[4] T. Ambrose, C.L. Chien, Phys. Rev. Lett. 76 (1996) 1743–1746.