Controlled synthesis of monodispersed superparamagnetic nickel ferrite nanoparticles

Article abstract of DOI:10.1016/j.ssc.2007.04.032

Nickel ferrite nanoparticles have been prepared through a gentle chemistry route, starting from iron nitrate, nickel nitrate and stearic acid. The nickel ferrite crystalline phase, the particle size and shape, and the homogeneity of the resulting nanoparticles were studied by X-ray diffraction and transmission electron microscopy. Fourier transform infrared techniques were used to study the composition characteristics of the as-prepared sample. Magnetization studies at room temperature showed superparamagnetic behavior for the nanoparticles. Magneto-optic rotation studies at different wavelengths of He-Ne lasers reveal non-linear behavior.

Full text of DOI:10.1016/j.ssc.2007.04.032

Solid State Communications 142 (2007) 702–705
www.elsevier.com/locate/ssc
Controlled synthesis of monodispersed superparamagnetic
nickel ferrite nanoparticles
P. Deba,∗, A. Basumallickb, S. Dasa
a
Department of Physics, Tezpur University, Tezpur 784028, India
b
Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711103, India
Received 22 December 2006; received in revised form 8 March 2007; accepted 21 April 2007 by D.D. Sarma
Available online 29 April 2007
Abstract
Nickel ferrite nanoparticles have been prepared through a gentle chemistry route, starting from iron nitrate, nickel nitrate and stearic acid. The
nickel ferrite crystalline phase, the particle size and shape, and the homogeneity of the resulting nanoparticles were studied by X-ray diffraction
and transmission electron microscopy. Fourier transform infrared techniques were used to study the composition characteristics of the as-prepared
sample. Magnetization studies at room temperature showed superparamagnetic behavior for the nanoparticles. Magneto-optic rotation studies at
different wavelengths of He–Ne lasers reveal non-linear behavior.
c
ꢀ 2007 Elsevier Ltd. All rights reserved.
PACS: 75.50.Tt; 75.75.ta; 81.40.Gh; 75.60.-d; 78.20.Ls
Keywords: A. Nanoparticles; B. Controlled synthesis; D. Superparamagnetic; E. Non-linear magneto-optic rotation
1. Introduction
with controlled size and composition are of fundamental and
technological interest. The preparation method determines
not only the products characteristics like size and shape,
but also their physical properties. Therefore, we report here
the synthesis of nickel ferrite nanoparticles through a novel,
simple, cost-effective and gentle chemistry route. The ability to
obtain single-phase nickel ferrite magnetic nanoparticles with
controllable particle size and size distribution will enhance its
acceptability in wide range of magnetic and magneto-optical
devices.
The increasing demand for oxide nanoparticles for use
as hard magnetic materials in ultra high density magnetic
storage media has laid emphasis on their preparation and
characterization because of their interesting and unusual
physical properties [1–5]. Among these oxide nanoparticles,
magnetic ones are the subjects of numerous interests due
to their wide range of potential applications, from recording
media to biological tagging [6–10]. Ferrites, the most widely
used magnetic oxides, exhibit interesting magnetic, electrical
and optical properties. Despite their physical resemblance
to ceramics, ferrites are unique among magnetic materials
because of their outstanding magnetic properties at high
frequency, along with their very high resistivity and inherent
high corrosion resistance. Though intense research effort has
been carried out on zinc, cobalt and barium ferrites/doped
ferrites, the study of nickel ferrite nanoparticles is yet to be
exploited [11–13]. It is commonly known that nanoparticles
2. Experimental
Initially, a homogeneous solution was prepared by melting
stearic acid at 80 ◦C and adding ferric nitrate Fe(NO3)3·9H2O
and nickel nitrate Ni(NO3)2·6H2O in suitable proportion. All
the reagents used for the experiment were of analytical reagent
grade. A reddish brown solution was formed which was stirred
continuously at 125 ◦C for two hours until all the brown
fumes of NO2 evolved out of the solution. A reddish brown
viscous mass was formed, which was allowed to cool in
air. The solidified mass so obtained was treated with 80 ml
tetrahydrofuran (THF) and stirred intensely for 15 min followed
∗
Corresponding author. Tel.: +91 03712 267007x5560; fax: +91 03712
267006.
E-mail address: pdeb@tezu.ernet.in (P. Deb).
c
0038-1098/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2007.04.032

P. Deb et al. / Solid State Communications 142 (2007) 702–705
703
as-prepared powder particles in KBr. The bands with the
peaks at 535.93, 675.07 and 814.21 cm−1 are assigned to the
deformation vibration of Fe–OH groups and the peak observed
at 3398.66 cm−1 is assigned to the stretching vibration of these
groups [14]. The bands with peaks observed at 1044.51 cm−1
and 1114.88 cm−1 can be assigned to O–H bending
vibration [15]. The 1313.19, 1343.58 and 1383.56 cm−1
peaks are attributed to the characteristic–CH3 bending. The
band observed between 1480 and 1700 cm−1 indicate the
presence of nitro compounds [15,16]. The peaks at 2840.51 and
2920.47 cm−1 are due to C–H stretching vibration [15,16]. The
above spectroscopic observation suggests that the as-prepared
sample consists of an intermediate/complex of stearates, nitro
compounds and residual stearic acid.
XRD studies were carried out on an as-prepared sample and
on a powder sample heat treated isothermally at 300 C for
Fig. 1. FTIR spectrum of the as-prepared powder precipitates.
◦
1 h. The XRD pattern of the as-prepared sample shown in
Fig. 2(c) does not exhibit any significant crystalline peak,
which corroborates the inferences drawn from the FTIR
spectroscopic studies. The XRD pattern of the heat-treated
sample (see Fig. 2(b)) shows the presence of nickel ferrite
only [17]. Hence, heat-treating the as-prepared sample in air
causes complete decomposition of the organic compounds and
evolution of nickel ferrite particles. A pattern decomposition
procedure using a pseudo-Voigt profile shape function [18] and
subsequent single line analysis based on the equivalent Voigt
representation [19] was used for the determination of crystalline
size and microstrain in the crystallite. The volume-weighted
mean crystalline size of nickel ferrite ha◦s been found to be
9 nm for the sample heat treated at 300 C for 1 h, and the
corresponding lattice strain is 0.65. The XRD pattern of the
sample heat treated at 400 ◦C exhibits the presence of NiO [20]
and α-Fe2O3 [21] along with NiFe2O4 peaks (refer Fig. 2(a)).
by centrifugation. The precipitated mass was then dried at
70 C in air oven for 10 h. Nanosized nickel ferrite particles
◦
were obtained by heating the as-prepared sample inside an
electrically heated furnace at the temperature 300 ◦C. The
desired temperature of the furnace was controlled by a PID
◦
controller with an accuracy up to ±1 C. Fourier transform
infrared spectroscopy (FTIR) studies were carried out on the as-
prepared sample to examine the compositional characteristics.
Microstructural characterization of the heat-treated sample was
studied by X-ray diffraction (XRD) using CoKα radiation
from a Philips PW-1830 diffractometer at 35 kV and 25 mA.
Despite the fact that transmission electron microscopy (TEM)
studies yield only a overall estimate about the particle size
distribution, this technique was used to supplement the results
of XRD studies. The magnetic characteristics, e.g. M–H
and M–T plots of the samples, were also studied. The
magneto-optic characterization of the so-prepared samples in
polyvinyl alcohol (PVA) medium was studied for three different
wavelengths of He–Ne laser beams.
◦
Hence with 400 C heat treatment, NiFe2O4 decomposes to
NiO and α-Fe2O3. Hence further characterization studies have
◦
been carried out on the sample heat treated at 300 C which
consists of NiFe2O4 only.
3. Results and discussion
Fig. 3(a) shows a TEM photograph of the sample obtained
after heating the sample at 300 ◦C. The particle size distribution
and subsequently the average particle size were evaluated from
the TEM micrograph by counting around 100 particles. The
estimated particle size distribution (see Fig. 3(b)) for the sample
The chemical and compositional characteristics of the
as-prepared powder precipitates were analyzed by FTIR
spectroscopy. Fig. 1 represents the FTIR spectrum of the
◦
◦
Fig. 2. XRD pattern of the (a) powder sample heat treated at 400 C, (b) powder sample heat treated at 300 C and (c) as-prepared powder.

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P. Deb et al. / Solid State Communications 142 (2007) 702–705
◦
Fig. 3. (a) TEM photograph of the sample obtained after heat treatment at 300 C and (b) the estimated particle size distribution.
Fig. 5. Magneto-optic rotation versus magnetic field for heat-treated
nanoparticles in PVA medium.
◦
Fig. 4. Hysteresis loop for the sample heat treated at 300 C.
stirred continuously until a brown viscous gel is formed. Then,
the magneto-optic rotation characteristic is studied. Initially,
has been found to be narrow, and it lies within the range
∼8–24 nm. The average particle size measured has been found
to be sim 11 nm, which is in close agreement with the XRD
results.
Fig. 4 show◦s the hysteresis loop plot for the sample heat
treated at 300 C for 1 h. Interestingly, it has been revealed
from the loop that the coercivity and remanence are almost
zero and the saturation magnetization value is 9.74 emu/g.
This is a characteristic of superparamagnetism [22]. The Curie
temperature, as obtained from the M–T plot, is around 210 ◦C.
These values are significantly different from the values for bulk
nickel ferrite particles reported elsewhere [23].
the rotation increases linearly with the increase in magnetic
field and later it becomes almost constant. The non-linear
behavior of superparamagnetic nickel ferrite clusters can be
explained by assuming the presence of an anisotropic axis along
which ferrite nanoparticles align. Here, superparamagnetic
nickel ferrite particles have an asymmetric distribution in
the matrix of PVA. Since these ferrites nanoparticles are
randomly dispersed inside the PVA matrix, but with a preferred
orientation along “anisotropy” axis, the external magnetic field
is exerting a torque. A preferred orientation should arise during
cluster formation as a consequence of magnetic or electrostatic
interaction between the ferrite nanoparticles and the applied
magnetic field or because of interaction between the ferrite
particles and the PVA matrix. Considering the equilibrium
between the electrostatic interaction and the magnetic torque,
a phase lag “ϕ” should exist between the magnetic field and the
anisotropy axis, which for small angles is proportional to the
applied torque. Since the torque tends to orient the magnetic
dipole parallel to the “anisotropy” axis and to the external
magnetic field, the amplitude of the rotation of magnetic dipoles
The magneto-optic rotation in varying magnetic field for
nickel ferrite nanoparticles embedded in polyvinyl alcohol
(PVA) was studied for three different color He–Ne lasers (refer
Fig. 5). For such a study, an optical medium is prepared by
dispersing nickel ferrite nanoparticles in PVA solution. First,
◦
20 ml of distilled water is taken and heated to 70 C until
a PVA and water solution is formed. Then, 0.25 g of the
sample heat treated at 300 ◦C is added to the PVA solution and

P. Deb et al. / Solid State Communications 142 (2007) 702–705
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705
linearly depends on the magnetic field for small magnetic
fields. At higher magnetic fields, the clusters are acting as units
themselves rather than the particles composing the clusters.
Hence, when rotated, the clusters behave as a permanent
magnetic dipole. Therefore, the rotation with the increase in
magnetic field tends to attain the saturation value. Moreover,
the magneto-optic values for a particular applied magnetic field
change with the change in laser light. The Verdet constant for
the nickel ferrite nanoparticles in PVA medium for different
He–Ne laser light has been calculated by using the slope of
the linear portion of the curves, and the values obtained are
1.616, 0.22 and 0.21 respectively for red, yellow and green laser
lights.
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4. Conclusion
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The reported synthesis method is suitable for the prepara-
tion of monodispersed nickel ferrite nanoparticles. The com-
positional characteristics reveal the presence of an interme-
diate/complex of stearates, which decomposes and liberates
nickel ferrite on heat treatment. XRD line profile analysis and
TEM studies confirm the presence of nickel ferrite nanopar-
ticles with average particle size ∼10 nm and corresponding
microstrain 0.65%. Superparamagnetic behaviour is obtained
in the samples. Non-linear behavior of magneto-optic rotation
characteristics is observed with varying magnetic field for the
nanoparticles in PVA medium.
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