Synthesis and characterization of nano silver ferrite composite

Article abstract of DOI:10.1016/j.jmmm.2010.01.036

We report the synthesis of nano sized silver ferrite composite having the empirical formula AgFeO₂ by a co-precipitation method. The resulting powders are thin platelets, transparent and a rich ruby red in color in transmission. The X-ray diffraction (XRD) powder data consisted of only nine reflections, and the analysis showed the unit cell to be rhombohedral. The powders showed extensive XRD line broadening and the sizes of the crystals are calculated to be in the range 4-36.5 nm. The morphology of the silver ferrite composite studied using scanning electron microscope showed nano sized particles. The particle size is found to increase with increase in annealing temperature. The magnetic behavior, measured using a vibrating sample magnetometer, indicated a change from paramagnetic to ferromagnetic with increase in particle size.

Full text of DOI:10.1016/j.jmmm.2010.01.036

ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 322 (2010) 2071–2074
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials
journal homepage: www.elsevier.com/locate/jmmm
Synthesis and characterization of nano silver ferrite composite
Y.L.N. Murthy a, T. Kondala Rao n,b, I.V. Kasi viswanath a, Rajendra Singh c
a Department of Organic Chemistry Andhra University, Visakhapatnam, India
b Government Degree and P.G. College for Men, Srikakulam-532001, India
c DRDO HQ, New Delhi, India
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the synthesis of nano sized silver ferrite composite having the empirical formula AgFeO2 by a
co-precipitation method. The resulting powders are thin platelets, transparent and a rich ruby red in
color in transmission. The X-ray diffraction (XRD) powder data consisted of only nine reflections, and
the analysis showed the unit cell to be rhombohedral. The powders showed extensive XRD line
broadening and the sizes of the crystals are calculated to be in the range 4–36.5 nm. The morphology of
the silver ferrite composite studied using scanning electron microscope showed nano sized particles.
The particle size is found to increase with increase in annealing temperature. The magnetic behavior,
Received 10 July 2009
Received in revised form
21 January 2010
Available online 1 February 2010
Keywords:
Nano size
Co-precipitation method
Silver ferrite composite
Rhombohedral
measured using
a
vibrating sample magnetometer, indicated
a
change from paramagnetic to
ferromagnetic with increase in particle size.
& 2010 Elsevier B.V. All rights reserved.
Ferromagnetic
Superparamagnetic
1. Introduction
and in magnetic refrigeration technology [7,8]. These applications
require biocompatible magnetic nanomaterials. Both silver and
ferrites meet these requirements but are not yet synthesized in the
nanoform. However the formation of bulk silver ferrite was reported
by Croft et al. [9]. For the first time we report here the synthesis,
characterization and magnetic studies of nano silver ferrite
composite.
Magnetic particles of the nanometer scale size are of interest
due to their technological applications and unique magnetic
properties which differ considerably from the bulk materials.
Magnetic particles with sizes less than the critical size become
single domain in contrast with the usual multi-domain structure
of the bulk magnetic materials exhibiting unique phenomena
such as superparamagnetism [1].
2. Experimental
Semiconductor technologies are developing magnetic random
access memories (MRAMS) where non-volatile magnetic dots are
used for storage in place of storage capacitors of a traditional
semiconductor. The storage media relating to today’s commercial
magnetic hard disks involve typical grain sizes of 10–20 nm at
approximately 103 grains/bit with a recording density of 1 G bit/in2.
The grains segregate randomly and introduce statistical noise into
the read-out signal due to the variation in grain size coercivity and
domain structure. Superparamagnetic behavior of grain size is the
primary requirement for reducing these fluctuations and to improve
the magnetic storage density and the superparamagnetic
limit imposes a minimum particle size of 10 nm [2]. Magnetic
nanoparticle systems exhibiting superparamagnetic behavior
display little or no remanence and coercivity while keeping a very
high saturation magnetization and have potential applications in
biomedicine [3,4], magnetic drug delivery, cell-sorting systems [5,6]
2.1. Materials
All the chemicals used in this study are of analytical reagent
grade. Silver nitrate, ferric nitrate, and sodium hydroxide
procured from M/s. Merck and BDH [Analar] have been used as
received.
2.2. Synthesis of nano silver ferrite composite
In a typical synthesis process, a mixture of 0.05 M silver nitrate
and 0.05 M ferric nitrate solutions in double distilled and de-
ionized water was stirred for 4 h at 27 1C, and then heated to 70 1C
for 1 h. 0.4 M (25 ml) solution of sodium hydroxide was prepared
and slowly added to the above solution by monitoring the pH of
the solution. The reactants were constantly stirred by a magnetic
stirrer until a pH level of 11–12 was reached [14] [15]. The stirring
was further continued for 6 h for aging. The resulting ruby-brown
precipitate was collected by filtration and washed with de-ionized
n Corresponding author. Tel.: +91 08942 224558.
E-mail address: kondalaraotata@gmail.com (T. Kondala Rao).
0304-8853/$ - see front matter & 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2010.01.036

ARTICLE IN PRESS
2072
Y.L.N. Murthy et al. / Journal of Magnetism and Magnetic Materials 322 (2010) 2071–2074
water for several times and then dried. The resulting powders are
found to be of rich ruby red color. These powders were annealed
at 400, 700 and 900 1C and subjected to XRD studies to
characterize the structure and determine the grain size.
be rhombohedral. The SEM images of these nano silver ferrites
annealed at 400 and 700 1C are shown in Figs. 2 and 3. SEM
images clearly show that surface morphology of the silver ferrites
is quite different with annealing temperature and the size of the
particles increases with increase in annealing temperature and
consistent with data obtained from XRD analysis. Further it is also
observed that nano sized silver ferrite composite crystals are
stable at 400 1C. At higher temperatures the composition is not a
single phase and the phase AgFeO2 decomposes irreversibly above
400 1C with loss of oxygen to yield both metallic silver and Fe2O3
or silver doped ferrites.
2.3. Instrumentation
X-ray diffraction pattern of the composite was recorded using
a Philips 1011 X-ray diffractometer (operating with 40 KV and
˚
a (1.5406 A) radiation. A Philips field effect
45 mA) with Cu K
(model XL 30) scanning electron microscope (SEM) with energy-
dispersive spectrometer (EDS) working at 30 kV was used to
examine the surface morphology and elemental composition of
the powders. The magnetization measurements of the samples
were carried out at room temperature using a Lakeshore-7400
vibrating sample magnetometer (VSM) with the applied magnetic
field in the range of ꢀ15 to 15 kG.
7000
2Ag2Fe2O4 -C4Agþ2Fe2O3 þO2
The size of the particles is observed to increase linearly with
annealing temperature, while annealing generally decreases the
lattice defects and strains. However it could also increase the
average size of the nanoparticles [8]. The nano silver ferrite
powders are observed to be rich ruby red colored thin platelets.
Microscopic and SEM observation of the platelets revealed that
some of them are six sided though the true symmetry is
rhombohedral [9] as characterized by XRD.
3. Results and discussion
The XRD pattern (Fig. 1) of powders annealed at 400, 700 and
900 1C clearly showed the formation of the nano silver ferrites.
The sizes of the silver ferrite particles calculated using the Scherer
formula at different annealed temperatures were found to range
between 4.5 and 36.5 nm as shown in Table 1. Notice from Table 1
that the size of the nanoparticles increases with increase in
annealing temperature. The analysis of XRD pattern with nine
reflections (curve labeled as (a) in Fig. 1 and inset) revealed
the unit cell present in the crystal structure of the silver ferrites to
The magnetic properties of these nanoparticles are analyzed
using a vibrating sample magnetometer (VSM). The VSM analyses
of the nano silver ferrite samples annealed at different tempera-
tures are shown in Fig. 4. The VSM data of silver ferrite composite
annealed at 400 1C show that the sample is paramagnetic in
nature. The magnetic remanence (MR=0.0023 emu/g) is found to
be very small (inset of Fig. 4) and shows high magnetic moment,
MS=1.10 emu/g, at an applied field of 15 kG. On the other hand,
silver ferrite composite annealed at 700 and 900 1C showed
ferromagnetic character (Fig. 4) with MR=0.035 emu/g,
MS=0.3833 emu/g and MR=0.069 emu/g, MS=0.3046 emu/g at
15 kG applied magnetic field. The parameters deduced from
VSM analysis of the samples are given in Table 1. It can be seen
Fig. 1. The XRDs of nano silver ferrite composite annealed at 400 1C (a), 700 1C (b)
and 900 1C (c). Sizes of the nano composite are 4.5 nm (400 1C), 32 nm (700 1C) and
36.5 nm (900 1C).
Fig. 2. SEM image of nano silver ferrite composite annealed at 400 1C.
Table 1
Various magnetic parameters of nano silver ferrite composite at different annealing temperatures.
Annealing temperature (1C) Particle size (nm) Saturation magnetization, MS (emu/g) at 15 kG Remanent magnetization, Coercivity, HC (kG) Magnetic nature
MR (emu/g)
400
700
900
4.5
32
36.5
high
0.002
0.035
0.069
0.002
0.548
0.785
Paramagnetic
Ferromagnetic
Ferromagnetic
0.383
0.305

ARTICLE IN PRESS
Y.L.N. Murthy et al. / Journal of Magnetism and Magnetic Materials 322 (2010) 2071–2074
2073
Fig. 3. SEM image of nano silver ferrite composite annealed at 700 1C.
Fig. 5. The variation in coercivity with size of nano silver ferrite composite.
The magnetization of different sized nanoparticles as
a
function of annealing temperature is shown in Fig. 4.
The magnetic nature not only depends on the variation of the
particle size but also depends on doping levels of Ag. Doping
decreases the strength of the exchange interactions, and leads to
the decrease in the value of the saturation of magnetization with
increase in particle size [13]. The saturation value of the
magnetization for smaller particles is found to be significantly
less than that of the bulk and approaches the bulk value with
increase in particle size. The smaller value of MS in smaller
particles is attributed to the greater fraction of surface spins and
leads to a superparamagnetic state and a smaller value of net
magnetic moment.
4. Conclusions
For the first time, we have successfully prepared single phase
materials of the AgFeO system. We conclude that the single phase
is not stable at above 400 1C .The onset of ferromagnetic order in
samples annealed at 700 and 900 1C suggests the decomposition
of the phase. The particle size of AgFeO2 annealed at 400 1C is
quiet small (4 nm).The simplicity and feasibility of making nano
AgFeO2 by our method seems very promising.
Fig. 4. The VSM data of nano silver ferrite composite annealed at 400, 700 and
500 1C.
from Table 1 that the coercivity of the samples increases with
increase in annealed temperature when particles are nano sized.
The very large coercivity and low saturation magnetization
observed at 900 1C is consistent with a pronounced growth of
magnetic anisotropy inhibiting the alignment of the moment in
an applied magnetic field. The remanence ratios at these
temperatures indicated the same feature, increasing from
0.0345 to 0.069 emu/g at room temperature (Table 1). The value
of remanence ratio of 0.5007 is very close to the expected value of
0.5 for a system of non-interacting single domain particles with
uniaxial anisotropy [10] even though the silver ferrite composite
has a rhombohedral structure. The existence of an effective
uniaxial anisotropy in magnetic nanoparticles is attributed to
surface effects [11]. Vibrating sample magnetometer data indicate
that as the particle size increases with annealing temperature the
paramagnetic nature of the composite changes to ferromagnetic.
Hence, it is expected that in between annealing temperatures of
400 and 700 1C the nanopowder could be in superparamagnetic
state. The coercivity of the nanoparticles is also studied as a
function of particle size at room temperature (300 K) [12] and is
shown in Fig. 5. The linear fit to the data shows that the coercivity
increases steeply with increase in size.
Acknowledgements
The authors are thankful to Shri B. Polisu, Principal,
Dr. T. Sivarao, Head, and other faculty members of the Depart-
ment of Chemistry, Government Degree and P.G. College for Men,
Srikakulam, India, for providing facilities and encouragement.
The authors are also grateful to Dr. B.V.R. Tata and Shri Ch.
Jagadeeswara Rao of IGCAR, Kalpakkam, India, for providing
spectral data.
References
[1] B. Martinez, A. Roig, X. Obradors, E. Molins, A. Rouanet, C. Monty, Magnetic
properties of g-Fe2O3 nanoparticles obtained by vaporization condensation in
a solar furnace, J. Appl. Phys. 79 (1996) 2580–2586.
[2] J. Dutta, H. Hofman, Nanomaterials, ‘‘http://www.nano.ait.ac.th’’, 2003,
p. 183.
[3] E.M. Chudnovsky, L. Gunther, Quantum theory of nucleation in ferromagnets,
Phys. Rev. B 37 (1988) 9455–9459.

ARTICLE IN PRESS
2074
Y.L.N. Murthy et al. / Journal of Magnetism and Magnetic Materials 322 (2010) 2071–2074
[4] C.C. Berry, A.S.G. Curtis, Functionalisation of magnetic nanoparticles for
applications in biomedicine, J. Phys. D: Appl. Phys. 36 (2003) R198–R206.
[5] Y.P. He, S.Q. Wang, C.R. Li, Y.M. Miao, Z.Y. Wu, B.S. Zou, Synthesis and
characterization of functionalized silica-coated Fe3O4 superparamagnetic
nanocrystals for biological applications, J. Phys. D: Appl. Phys. 38 (2005)
1342–1350.
[6] J.K. Ruuge, A.N. Ruzetski, Magnetic fluids as drug carriers: targeted transport
of drugs by a magnetic field, J. Magn. Magn. Mater. 122 (1993) 335–339.
[7] N.M. Pope, R.C. Alsop, Y.A. Chang, A.K. Smith, Evaluation of magnetic alginate
beads as a solid support for positive selection of CD34+ cells, J. Biomed.
Mater. Res. 2 (1994) 449–457.
[10] R.J. Willey, S.A. Oliver, G. Oliveri, G. Busca, Chemistry and structure of mixed
magnesium ferric oxide aero gels, J. Mater. Res. 8 (1993) 1418–1427.
[11] R.G. Kulkarni, H.H. Joshi, Comparison of magnetic properties of MgFe2O4
prepared by wet-chemical and ceramic methods, J. Solid State Chem. 64
(1986) 141–147.
[12] C. Liu, A.J. Rondinone, Z. Zhang, Synthesis of magnetic spinel ferrite CoFe2O4
nanoparticles from ferric salt and characterization of the size-dependent
superparamagnetic properties, J. Pure Appl. Chem. 72 (2000) 37–45.
[13] B. Parveteswra Rao, G.S.N. Rao, A. Mahesh Kumar, K.H. Rao, Y.L.N. Murthy,
S.M. Hong, Chong-oh kim, Cheolgi kim, J. Appl. Phys. 101 (2007) 123902-1–
123902-4.
[8] M.R. Zachariah, M.I. Aquino, R.D. Shull, E.B. Steel, Formation of super-
paramagnetic nanocomposites from vapour phase condensation in a flame,
Nanostruct. Mater. 5 (1995) 383–392.
[14] M.K. Shobana, S. Sankar, Synthesis of characterisation of Ni(1-x)Cox Fe2O4
nanoparticles, J. Magn. Magn. Mater., 2009, doi:10.1016/J.Jmmm.2009.05.08.
[15] T. Kondalarao, I.V. Kasiviswanath, Y.L.N. murthy, Defluoridation of water
[9] W.J. Croft, N.C. Tombs, R.E. England, Crystallographic data for pure crystalline
silver ferrite, Acta Crystallogr. 17 (1964) 313–314.
by nano technology, Water Sci. Technol.: Water Supply
485–492.
9 (5) (2009)