Synthesis, structural, dielectric and magnetic properties of CuFe2O4/MnO2 nanocomposites

Article abstract of DOI:10.1016/j.jmmm.2016.12.009

Novel nanocomposite of (1-x)CuFe₂O₄/xMnO₂ [x=10% to 50?wt%] has been synthesized by two step wet chemical route without impurity. The x-ray diffraction analysis shows the formation of both phases with crystallite size 40–100?nm which is consist ant with estimated size of SEM.The FTIR spectra confirms the characteristics vibration of ferrites atoms at tetrahedral and octahedral sites along with Mn-O vibration mode, which also confirms the coexistence of both phases. The dielectric properties studied by LCR meter in frequency range of 1?K Hz to 2?MHz.The dielectric constant and tangent loss shows same dispersion of ferrites while a.c. conductivity decreases with increase in MnO₂ contents. The real and imaginary part of impedance also calculated which shows decreasing trend at higher frequency. The magnetic characterization performed by vibrating sample magnetometer (VSM) at room temperature, which shows normal ferromagnetic behavior of ferrites but saturation magnetization and coercivity decreases with incorporation of MnO₂ contents.

Full text of DOI:10.1016/j.jmmm.2016.12.009

Author’s Accepted Manuscript
Synthesis, Structural, Dielectric and Magnetic
properties of CuFe O /MnO Nanocomposites
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Kashif Ali, Ali Bahadur, Abdul Jabbar, Shahid
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Synthesis, Structural, Dielectric and Magnetic properties of
CuFe2O4/MnO2 Nanocomposites
Kashif Ali1, Ali Bahadur2, Abdul Jabbar3, Shahid Iqbal4, Muhammad Imran Bashir5
1Department of Physics, International Islamic University, Islamabad, Pakistan
2Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan.
3Department of Chemistry, Allama Iqbal Open University, Islamabad, Pakistan.
4School of chemistry and chemical engineering, university of Chinese academy of sciences, Beijing, 10049.PR
China.
5Department of Physics, Quaid-i-Azam University, Islamabad, Pakistan.
Abstract
Novel nanocomposite of (1-x)CuFe2O4/xMnO2 [x=10% to 50wt%] has been synthesized by
two step wet chemical route without impurity. The x-ray diffraction analysis shows the
formation of both phases with crystallite size 40-100nm which is consist ant with estimated
size of SEM.The FTIR spectra confirms the characteristics vibration of ferrites atoms at
tetrahedral and octahedral sites along with Mn-O vibration mode, which also confirms the
coexistence of both phases. The dielectric properties studied by LCR meter in frequency
range of 1KHz to 2MHz.The dielectric constant and tangent loss shows same dispersion of
ferrites while a.c. conductivity decreases with increase in MnO2 contents. The real and
imaginary part of impedance also calculated which shows decreasing trend at higher
frequency. The magnetic characterization performed by vibrating sample magnetometer
(VSM) at room temperature, which shows normal ferromagnetic behaviour of ferrites but
saturation magnetization and coercivity decreases with incorporation of MnO2 contents.
Keywords: Ferrites, Dielectric, Magnetic, Coercivity, a.c. Conductivity, Scanning Electron
Microscopy (SEM).
Page 1 of 25

1. Introduction
Materials showing simultaneously substantial dielectric and magnetic properties have been of
great interest to modern science and technology, not only from the perspective of solid state
physics, but also because of their potential for several applications in electronic devices and
systems [1-3]. In recent years, the evolution of high-speed digital electronics, wireless
communications, industrial, medical and associated increasing exposure to microwaves
necessitates the development of effective, condensed, and economical absorbers of
electromagnetic energy to ensure electromagnetic compatibility and environmental safety in a
wide frequency range. Ferrites retain a unique combination of high permittivity, low
dielectric loss, spontaneous saturation magnetization, facile and cheap synthesis techniques
and extremely low d.c. conductivity which makes them fascinating for developing wideband
microwaves absorbers [4-9].
The main problem with the development of polymeric and metal oxides composites filled
with ferrite powders is how to control frequency dispersion of complex permeability and
permittivity of composites. This can be achieved by variation of the composite filler types,
size and shape of host, their distribution within sample, concentrations and morphology of
mixtures. Several attempts are also made to control the magnetic and dielectric properties of
materials by different synthesis techniques including chemical vapour deposition (CVD) [10],
hydrothermal [11], physical vapour deposition (PVD) [12], electrospinning [13, 14], Sol–gel
spinning [15] and coprecipitation [16]. The co-precipitation is facile, cheap, low time
consuming and versatile method in which the precursors are easily available for synthesis of
nanoscale materials.
Several researchers have addressed the challenge of finding a radar-frequency absorbing
material with wide frequency bandwidth [17-19]. Since materials based only on hexaferrites
cannot fulfill these demands, multilayer structures were explored in order to combine
Page 2 of 25

hexaferrites with other materials having different resonant frequencies and new systems of
composite powders including hard and soft materials have been developed [20-24]. The
reported results correspond to samples where both phases are simultaneously grown, such as
SrFe12O19 / α-Fe2O3, CoFe2O4 / ZnFe2O4, BaFe12O19 / Ni0.8 Zn0.2 Fe2O4, BaFe12O19 / Fe3O4
[25-29].
Manganese dioxide (MnO2) nanostructures have been extensively used as catalysts [30], ion
filters [31], electrochemical supercapacitors [32, 33], and electrode materials in Li/MnO2
batteries [34]. Furthermore MnO2 possesses more distinctive chemical and physical
properties which are strongly dependent on the morphology and nanostructure of manganese
dioxides [35]. Manganese dioxide has been also used to synthesize different metal-ceramic
materials [36, 37].In recent year; several research groups have investigated the microwave
absorbing materials of the MnO2 nanoparticles [38–40]. However, the influence of the
morphology of MnO2 nanostructures on the microwave EM characteristics and absorption in
gigahertz frequency range has been rarely investigated and Copper ferrite, a soft magnetic
material with tetragonal spinel structure, has significant reflection loss values at lower
frequencies (MHz range). The content of MnO2 phase was systematically varied to study its
effect on the overall dielectric and magnetic properties of the nanocomposite and impedance
analysis has also been studied when both phases are coexistent.
In this work, (1-x) CuFe2O4/xMnO2 { x = 10 to 50 wt.%} nanocomposites has been prepared
by two-step wet chemical co-precipitation method already reported in our previous work
[16] investigated the effect of MnO2 contents on dielectric and magnetic properties of
CuFe2O4.
Page 3 of 25

2. Experimental section
2.1 Synthesis of CuFe2O4
In the first step, 0.4 M (25ml) solution of iron chloride (Sigma Aldrich) and 0.2M (25ml)
solution of copper chloride were mixed in doubly distilled water to avoid the addition of any
impurity atom in the final solution. 3M (25ml) solution of sodium hydroxide (Duckson) was
slowly added in the previous solution. The pH of solution was constantly monitored under
magnetic stirring until PH level of 11-12 was reached. The liquid precipitate was then
0
brought to a reaction temperature of 80 C for one hour and the product was cooled to room
temperature. The prepared precipitate was washed with distilled water to remove any
impurity atom of sodium and chlorine compounds. The beaker content was centrifuged for
ten minutes at 3000 rpm to isolate the precipitate from the solution. The precipitate was then
dried overnight at 1000C.
2.2 Synthesis of MnO2
In the second step, 0.2M (100ml) solution of KMnO4 and 0.2M (100ml) solution of
MnCl2.2H2O are prepared in distilled water to avoid addition of impurity.3M (100ml)
solution of NaOH is prepared separately and added dropwise in previous solution to obtain
black precipitate of MnO2.Few drops of HCl is added to adjust PH value in final solution.
The black precipitate is filtered and washed with distilled water and ethanol to remove
impurities in final product. The precipitate is brought to reaction temperature at 60C for one
hour and dried overnight at 100C to remove water contents. The dried sample is grinded into
fine powder.
Page 4 of 25

2.3 Synthesis of (1-x) CuFe2O4/xMnO2 Nanocomposite
The nanocomposites of (1-x)CuFe2O4/xMnO2 is obtained by following our previous synthesis
technique [16] in which different weight percent (10% to 50 wt.% ) of metal oxide (MnO2)
0
is added in CuFe2O4 nano powders and annealed at 600 C for five hours to obtain the
required nanocomposites.
3. Results and Discussion
3.1 X-ray Diffraction Analysis
To study the structural properties and crystalline phases of CuFe2O4, MnO2 and their
nanocomposites, XRD analysis has been carried out separately at room temperature with step
size of 0.2° (2θ) and 2θ range of 20°–80° with Cu Kα radiation having wavelength 1.54Å.
Figure 1(a) shows the XRD pattern for CuFe2O4 sample annealed at 6000C for 5 hours.
Comparing to the XRD data files, it has been found that all peaks position match those for the
pure CuFe2O4. The peaks position and their corresponding (hkl) planes are as follows;
18.3440 (111), 30.1760 (220), 35.5440(311), 43.2000 (400), 53.5980 (422), 57.1370 (511),
62.7460 (440) corresponding to inverse spinal tetragonal crystal structure of CuFe2O4 [16].
The XRD pattern of MnO2 nanoparticles is depicted in Figure 1(b). All the diffraction peaks
are well indexed to the tetragonal structure (PCPDFWIN) with lattice constants of a = b =
9.785 A0, c = 2.863 A0 and a = b = c = 900. The average crystalline size was estimated using
Debye – Scherer formula [41] which lies in the range of 40-80nm.
A sharp strong diffraction peak depicted in Figure (2) demonstrates that the MnO2
nanoparticles are well crystallized in the lattice planes. No impurity peak is observed which
indicates the high purity of the as prepared products. Hence the X-ray diffraction pattern
confirms the formation of both phases, which are coexistent in this nanocomposite.
Page 5 of 25

3.2 FTIR Analysis
The structure information and component of samples were also identified by the FT-IR
spectra. The characteristic peaks at 1620 cm−1 and 3400 cm−1 are assigned to the bending
vibration and stretching vibration of O-H. Whereas the absorption peak near 711 cm-1, 523
cm-1 and 467 cm-1 is considered as the characteristic absorption peak of Mn-O bond (Figure
3). Compared to the coarse-grained α-MnO2, the red shifts of the characteristic absorption
peak were observed for α-MnO2 [42], which was assigned to a typical quantum effect of
nanoparticles.
3.3 SEM Analysis
The morphology and particle size of prepared sample has been analyzed by Scanning
Electron Microscopy (SEM).The SEM images shows that particle lies in the range of 40-
118nm with spherical morphology and there is uniform distribution of particles with spherical
symmetry and no agglomeration was observed in this sample. Moreover with the increase in
MnO2 contents in CuFe2O4 magnetic nanoparticles ,the particles size increases due to
increase in grain growth as can be seen in figure [ 4 (a to d)].
4. Dielectric properties
4.1 Dielectric Properties
In ferrite materials, the dielectric properties can be described as a function of frequency of
applied electric field, microstructure, temperature, grain size, nature of dopant, crystal
structure and other parameters. The dielectric response in ferrite material can be briefly
defined by expressing the relative dielectric constant as a complex quantity made up of real
and imaginary components, i.e.
*
/
//
Ɛ = Ɛ +iƐ
(1)
Page 6 of 25

/
//
Where Ɛ and Ɛ are the real and imaginary part of dielectric constant respectively ,
representing the amount of energy stored in a dielectric material as polarization and the
energy loss respectively, while applying an electric field. In order to understand the influence
of electric field on microstructure, composition and intergranular potential barrier on the
electrical properties of ceramic, the frequency dependent real dielectric constant can be
calculated by LCR meter at room temperature using the relation:
/
Ɛ= Ct/AƐ0
(2)
Where C is the capacitance of the specimen in Farad (F), t is thickness of pellet; Ɛ0 is the
permittivity of free space. (8.854*10-12- F/m) and A is the cross sectional area of the flat
surface of the pellet. The dissipation factor or tangent loss for all the samples was measured
simultaneously during capacitance from LCR meter. Where tangent loss is the dielectric loss
tangent which is proportional to the loss of energy from the applied field into the sample (this
energy is dissipated as heat) and therefore denoted as dielectric loss.
Figure [5(a)] shows the variation of real part of dielectric constant with respect to the
frequency
of applied electric field between the ranges of 1KHz to 2 MHz for all the samples. It
is observed that the dielectric constant decreases with increase in MnO2 concentration from
10 wt.% to 50 %).The decrease in dielectric constant indicates the formation of
microstructure with semiconducting MnO2 grains surrounded by insulating grain boundaries
and also suggest the existence of interface states in the grain boundaries. It is also evident
from [5(a)] that all the samples show same dielectric dispersion. The dispersion is rapid at
lower frequencies but it is slow and approaches to almost frequency independent behavior at
high frequency. The observed dielectric behavior can be explained in the light of Maxwell–
Wagner interfacial type of polarization [43,44] and Koop’s phenomenological theory [45].
Page 7 of 25

According to this model, a dielectric medium is assumed to be made of well conducting
grains which are separated by poorly conducting (or resistive) grain boundaries. The grain
boundaries are found to be more effective at lower frequencies, while grains are effective at
higher frequencies. The grain boundaries are formed during the sintering process due to the
superficial reduction or oxidation of crystallites in a porous material as a result of their direct
contact with the firing atmosphere [46, 47].
The frequency independent behavior of all the samples at higher frequency of applied electric
field is just because of the charge carriers which are responsible for different mechanisms of
polarization and that lag behind the applied alternating field. As a result they cannot follow
the changes in the applied field over a certain frequency limit, as the frequency increases.
Dissipation factor or tangent loss in figure [5(b)] which is the heat dissipation due to domain
wall motion and polarization rotation in the samples is also calculated and all samples shows
same behaviour ,at low frequency larger amount of heat is dissipated because the field follow
the domain wall and at higher frequency, the polarization rotation does not follow the field
and dissipation factor decreases which seems to be remains constant at higher frequency
.Moreover the composition dependence of dissipation factor shows that larger amount of heat
is dissipated at 10 wt.% contents of MnO2 and lower amount of heat dissipation occurs at
concentration of x > 20 wt.%.
4.2 A.C. Conductivity
/
The ac conductivity of a dielectric sample is calculated using relation σAC =2πfε0ε tanδ
[K.M.Batoo et al., 2009]. Figure [6] shows the variation of ac conductivity of pure CuFe2O4
and its nanocomposites with MnO2 nanoparticles at room temperature. It is clear from the
graph hat the conductivity increases as the frequency of applied ac field increases. It is also
evident from a.c. conductivity graph that the ac conductivity decreases as the MnO2 content
Page 8 of 25

increases. It can be attributed to the fact that presence of Mn+2 ions occupy the Fe+3 lattice
site and reduce the concentration of trivalent ions at octahedral sites and reduce the jumping
of electron from Fe+2 to Fe+3 ions as a result of which the electrical conductivity decreases.
The second possibility of decrease in conductivity is growth of grain size that enhances
insulating non conducting domain walls. The conductivity of dielectric materials is
temperature and Frequency dependent, and obeys the empirical formula of frequency
dependence and is governed by the ac power law [48].
5. Impedance Analysis
Impedance spectroscopy is an important tool to completely understand the origin of
conducting mechanism and electrical properties of the ferrite ceramics and their
nanocomposites in terms of microstructure and composition, by observing the contributions
from grains, grain boundaries or electrodes [26, 27]. It also provides the data for both
resistive (real part) and reactive (imaginary part) contribution to conductivity under applied
A.C. field. Figures [7(a)&(b)] shows the variation of real and imaginary part of impedance
with frequency and it can be seen that the impedance values are monotonically decreasing
with increase in frequency and this behaviour attributed to increase in conductivity at higher
frequency as can be seen in figure.[6]. High impedance value at low frequency is enumerates
the space charge polarization at the interface of composites due to difference in permittivity
(Ɛ1, Ɛ2). This space charge polarization exists at the interfaces of materials having more than
one phase. At higher frequency the impedance values are merged due to release in space
charge carriers. In the case of spinel ferrites ceramics, particularly, the interactions between
the grains and grain boundaries are better resolved [51]. Figure [8] shows the complex
impedance plane plots (Cole-Cole plots) at room temperature for all samples at different
concentration .It is indicated from graphs that there are two well-resolved semi-circular arcs,
a larger one at low frequency and a smaller one at the higher frequency side. The arcs at the
Page 9 of 25

low frequency sides are assigned to the contributions from the grain boundary region and arcs
at higher frequency are due to contribution from grains respectively [52].
6. Magnetic Properties
The magnetic properties of prepred sample has been analysed by Vibrating Sample
Magnetometer (VSM) under applied field of + 7 KOe at room temperature. Figure [9] shows
the hysteresis loops of pure CuFe2O4 nanoparticles while Figure [10] exhibits hysteresis loops
when copper ferrite nanoparticles were combined with the manganese oxide to form the
desired nanocomposite. All the composition shows the same ferromagnetic behavior that
change drastically with incorporation of MnO2. It is clear from M-H loops that a drastically
change in saturation magnetization and coercivity is observed from 10% to 50wt.% addition
of MnO2 concentration and slight decrease in these magnetic properties were observed at
higher concentration of MnO2 up to 50wt%. The decrease in saturation magnetization can be
understood based on the fact that MnO2 has nonmagnetic character at the room temperature,
hence with an increase in the MnO2 concentration in our sample one would expect the
saturation magnetization to decrease. In this context we also notice that when the
concentration of MnO2 becomes the largest (x=50%), magnetism in our nanocomposite
sample almost diminishes.
Interestingly we also notice that with MnO2 concentration increase, coercivity of MnO2-
CuFe2O4 nanocomposite decreases. This is very remarkable, considering that with increasing
the MnO2 concentration, the resultant MnO2-CuFe2O4 composite’s size also increases and as
it is well known that the coercivity of the nanoparticles increases with the volume increase
[53]. This observed decrease needs to be explored further. Currently we believe it to be
originating from the fact that with increasing concentration of CuFe2O4 on the MnO2 powder,
surface defects and pores are covered with the copper ferrite nanoparticles Along with this,
Page 10 of 25

there may be pinned spins of copper ferrite present on the surface and these two effects can
produce a net decrease in the surface anisotropy of our nanocomposite sample which results
in the smaller coercivity values.
Conclusion
In this study, the novel magnetic nanocomposites have been prepared by facile wet chemical
method without impurity. The x-ray diffraction and FTIR analysis confirms the coexistent of
both phases. The SEM images reveal the formation of spherical morphology without
agglomeration of grains. The dielectric constant, Coercivity and saturation magnetization
decreases with increase in MnO2 contents. The incorporation of MnO2 contents shifts this
material to soft magnetic with low value of dielectric constant. This type of material can be
used in electromagnetic shielding application.
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Captions:
Figure [1(a)] XRD pattern of pure CuFe2O4 annealed at 6000C for 6 hours.
Figure [1(b)] XRD Pattern of Pure MnO2 annealed at 600 0C for 6 hours.
Figure [2] XRD Pattern of (1-x) CuFe2O4/xMnO2 [x=10% to 50wt. %] annealed 600 0C for 5
hours.
Figure [3]: FTIR absorbance spectrum of (1-x)CuFe2O4/ xMnO2.
Figure [4] SEM images of (a) Pure CuFe2O4 (b) 20% MnO2(c) 40% MnO (d) 50% MnO2.
Figure [5 (a)] Dielectric constant versus frequency of (1-x) CuFe2O4/xMnO2 [x=10% to 50wt.
%] annealed 600 0C for 5 hours.
Figure [5 (b)] tangent loss versus frequency of (1-x) CuFe2O4/xMnO2 [x=10% to 50wt. %]
annealed 600 0C for 5 hours.
Figure [6] A.C.conductivity versus frequency of (1-x) CuFe2O4/xMnO2 [x=10% to 50wt. %]
annealed 600 0C for 5 hours.
Figure [7 (a)] Real part of impedance versus frequency of (1-x) CuFe2O4/xMnO2 [x=10% to
50wt. %] annealed 600 0C for 5 hours.
Figure [7 (b)] Imaginary part of impedance versus frequency of (1-x) CuFe2O4/xMnO2
[x=10% to 50wt. %] annealed 600 0C for 5 hours.
Figure [8] Cole-Cole plots of (1-x) CuFe2O4/xMnO2 [x=10% to 50wt. %] annealed 600 0C for
5 hours.
Figure [9] M-H Loops of pure CuFe2O4 at room temperature.
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Figure [10] M-H Loops of xMnO2/CuFe2O4 (1-x) [x=10% to 50Wt. %] nanocomposites at
room temperature.
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Figure-1 (a)
Figure-1 (b)
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Figure-2
Figure-3
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Figure-4
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Figure-5 (a)
Figure- 5 (b)
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Figure-6
Figure-7 (a)
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Figure-7 (b)
Figure-8
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Figure-9
Figure-10
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