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FINAL REPORT
UGC-Minor Research Project
[File No: 47-561/08 (WRO)]
Title: Influence of substitution of Cu and Mn on
magnetic, electric and dielectric properties of
Ni0.6-xRxZn0.4Fe2O4 (R=Cu and Mn and x=0.0-0.6)
Name of the Principal Investigator: Dr. Umesh B. Gawas
Name of the Institution:
DM’s College of Arts,
Sou. Sheela Premanand Vaidya College of Science and
V.N.S. Bandekar College of Commerce,
P.V.S. Kushe Nagar, Assagao- Mapusa, Goa
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UNIVERSITY GRANTS COMMISSION
BAHADUR SHAH ZAFAR MARG
NEW DELHI – 110 002
Annual Report of the work done on the Minor Research Project
1. Project report No. 1st/2
nd/3
rd / Final : Final
2. UGC Reference No. : File No. 47-561/08(WRO), dated 15/1/2009
3. Period of report : March 2009 to March 2013
4. Title of research project :
Influence of substitution of Cu and Mn on magnetic, electric and dielectric properties of
Ni0.6-xRxZn0.4Fe2O4 (R=Cu and Mn and x=0.0-0.6)
5. (a) Name of the Principal Investigator : Dr. Umesh B. Gawas
(b) Dept. and University/College where work has progressed: Department of Chemistry,
DM‟s College of Arts, Sou. Sheela Premanand Vaidya College of Science and
V.N.S. Bandekar College of Commerce, P.V.S. Kushe Nagar, Assagao- Mapusa,Goa.
6. Effective date of starting of the project: 1st March 2009
7. Grant approved and expenditure incurred during the period of the report:
a. Total amount sanction : Rs. 1,85,000 /-
b. Total amount released : Rs. 1,45,000 /-
c. Total amount utilised : Rs. 1,44,743 /-
c. Report of the work done : Enclosure
i. Brief objective of the project:
The main objective of the project is in studying the effect of the substitution of Cu and
Mn on magnetic, electric and dielectric properties of Ni0.6-x RxZn0.4Fe2O4 (R= Cu, Mn
and x = 0.0- 0.6 ) and to develop an synthestic strategy which can be used to prepare
ceramic material with optimum properties suitable for the practical applications.
ii. Work done so far and results achieved and publications, if any, resulting from the work
(Give details of the papers and name s of the journals in which it has been published or
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accepted for publication) : ---
iii. Has the progress been according to original plan of work and toward achieving the
objective. if not, state reasons : Yes
iv. Please indicate the difficulties, if any, experienced in implementing the
project : --
v. If project has not been completed, please indicate the approximate time by which it is
likely to be completed. A summary of the work done for the period (Annual basis) may
please be sent to the Commission on a separate sheet : Completed
vi. If the project has been completed, please enclose a summary of the findings of the study
Two bound copies of the final report of work done may also be sent to the Commission:
vii. Any other information which would help in evaluation of work done on the project. At
the completion of the project, the first report should indicate the output, such as (a)
Manpower trained (b) Ph. D. awarded (c) Publication of results (d) other impact,
if any : 03 Publication in Conference /symposium
SIGNATURE OF MINOR PROJECT SIGNATURE OF PRINCIPAL
RESEARCHER
(Dr. Umesh B. Gawas) (Dr. D. B. Arolkar)
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Project Summary
1. Introduction
Ferrites are ceramic, homogeneous magnetic materials composed of various oxides
with iron oxide as their main constituent. The technology of ferrites and magnetic ceramics
has assumed a new importance during the last several decades especially in the last few years
because of their interesting electrical and magnetic properties which are useful in
applications such as information storage systems, magnetic bulk cores, magnetic fluids,
microwave absorbers, medical diagnostics etc [1]. The most recent reason for upsurge in
ferrite interest has been the development of the new, small, efficient power supplies using
solid state switching called switch mode power supplies (SMPs). These SMP‟s are the
integral components of modern day electronic equipments such as computers, laptops and
entertainment applications. Besides the ease of preparation and low manufacturing cost, the
advantage of spinel ferrites is their high magnetic permeability and high electrical resistivity.
Also these materials can be shaped in a variety of different geometries meant for specific
applications.
Nickel zinc ferrites are characterized by high material resistivity suitable for high
frequency applications from 1MHz to several hundred megahertz‟s. Hence, these ferrites find
use in microwave devices, power transformer, rod antennas, read/write heads for high speed
digital tapes [2]. Use of nickel zinc ferrites is limited due to their low permeability at higher
frequencies and increasing cost. Manganese zinc ferrite on the other hand posses high
permeability and saturation magnetization with nearly zero magneto-crystalline anisotropy
and magneto-restriction. Hence these ferrites find use in transformer cores, noise filters,
recording heads etc [3]. Manganese zinc ferrites also have certain limitations for magnetic
applications at high frequencies, because of their low resistivity and hence high eddy current
losses. For high frequency magnetic applications, ferrite materials with high permeability as
well as high resistivity are more suitable which can reduce eddy current losses. Therefore, an
appropriate combination of these two ferrites can result in the material with enhanced
properties, more suitable for high frequency applications [4]. It is well established fact that,
the magnetic and electrical properties of ferrites are sensitive to the cation distributions,
which in turn depend on the method of synthesis. Hence, there is growing interest in the
newer and newer synthetic strategies to improve on the properties of ferrite materials
Recently surface mounting device (SMD) has been developed rapidly with
development of ceramic electronics and information technology. As one of the most
important SMD, Multiplier Chip Indicator (MLCI) made from soft ferrite become more and
more miniaturized and integrated and this required that the soft ferrites be co-fired with
internal contact material layer by layer considering the conductivity and cost. Pure silver is
the most suitable contact material. Chip inductors are one of the passive surface mount
devices, which are important components for the latest electronic product such as cellular
phones, video cameras, notebook computers, hard and floppy drives etc. which require small
dimension, lightweight and better functions [5]. Nickel copper zinc ferrites are well
established magnetic materials for multilayer chip inductor applications because of their
relatively low sintering temperature, high permeability in the RF region and high electrical
resistivity [6,7]. For multilayer chip inductor application, the ferrite needs to be sintered at <
950oC in order to bond with the internal silver electrode during the manufacturing of
multilayer chip inductor applications. To decrease the sintering temperature fine ferrite
powder with the non-stoichiometry ratio of Ni-Cu-Zn in the starting chemical composition
must be used. It is known that the magnetic properties of spinel ferrites are strongly
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dependent on the microstructures. Small amount of additives are often used for
microstructure refinement. The rare earth oxides are becoming the more promising additives
for the improvement of the ferrites properties.
It is well established fact that, the magnetic and electrical properties of ferrites are
sensitive to the cation distributions, which in turn depend on the method of synthesis. Hence,
there is growing interest in the newer and newer synthetic strategies to improve on the
properties of ferrite materials.
2. Experimental details: Synthesis of Ni0.6-xRxZn0.4Fe2O4 [(R=Cu, Mn) (x = 0.0-0.6)]
2.1. Combustion synthesis: Principle
The combustion process is an exothermic reaction between an oxidizer and a fuel.
When the heat evolved is more than the heat requires for the reaction, the system becomes
self-sustained. Also, the exothermicity of such reactions takes the system to a high
temperature. Hence, this process, popularly known as self- propogating high temperature
synthesis (SHS) is also called furnaceless or fire synthesis. The interesting feature of this
process is that the sample once ignited continues to burn to consume itself. In any combustion
process, the reactant mixture (fuel and oxidiser) can be hypergolic (ignite by contact) or is
ignited in a controlled way by an external source. The residue or the ash that emerges after
complete combustion is the oxide material. Of late, this ash has been recognized to be of
great technological interest. By use of the combustion method, a number of useful oxide
materials for various applications such as refractory, magnetic, dielectric, semiconducting,
insulators, catalysts, sensor, phosphor etc. have been synthesized. Recently, attempts have
been made to modify SHS so as to eliminate and overcome some of the ensuring problems by
using various innovative synthetic strategies, with a similar view, carrying out the reaction in
solution form has made a different approach to SHS. This approach called the solution
combustion method and it uses a solution of the redox mixture.
The combustion process by the mixture method is carried out as follows:
Redox mixture: The redox mixture is made up by mixing a stoichiometric amount of the
metal nitrate or perchlorate with urea or hydrazide derivative (fuel) and igniting at
temperature between 300°C and 350°C. The mass left after complete combustion is the oxide
material. This method uses the experiences of propellant chemistry in making the redox
mixture. The stoichiometry or the equivalence ratio ( ɸe , O/F ) at which the total combustion
reaction takes place is very important and crucial. Combustion may not take place at all, if the
stoichiometry is not maintained. The calculation of the equivalence ratio is based on
balancing the oxidising (O) and reducing valency (F) of the reactants. The energy released by
the combustion of the redox mixtures will be maximum when the equivalence ratio (ɸe, O/F)
is unity (O is the total oxidising and F is reducing valency of the components.) In propellant
chemistry, the elements C, H and metal ions are considered as reducing species. E.g., C= +4,
H = +1, M+2
= +2 , M+3
= +3 , M+4
= +4 , etc. O is considered as oxidiser with a valency of -2
and N is considered to have zero valency.
2.2. Materials
All reagents used were of analytical grade and are used without further purification.
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2.3. Experimental
The hexamine to nitrate ratio was calculated by using the oxidizing and reducing
valences of the metal nitrates and hexamine. Stoichiometirc quantities of metal nitrate (Mn,
Ni, Cu, Zn, Fe) were melted by heating on the hot plate. To the hot melted stoichiometric
quantity of finely powdered hexamine was added and stirred till the slurry was obtained. The
slurry was kept in preheated furnace maintained at 300oC for 20 minutes. The hexamine
nitrite mixtures froths and finally ignites leaving brown coloured residue of the mixed metal
oxides and the residue was found to be magnetic.
9[R(NO3)2 + Ni(NO3)2 + Zn(NO3)2 ]+ 18 Fe(NO3)3 + 10(CH2)6N4
9R-Ni-Zn-Fe2O4 (s) + 60CO2 (g) + 56N2 (g) + 60H2O(g) [R=Mn,Cu]
3. Characterization of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
3.1. XRD pattern of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The XRD patterns of all the Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6)
ferrites are presented in Fig. 2.1a. The X-ray diffractograms displays all the peaks
characteristics of the cubic spinel ferrites which confirm the formation of these ferrite
samples. The broadening of XRD peaks is indicative of the ultrafine (nanocrystalline) nature
of all Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites
Fig.1. (a) XRD pattern of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites, (b) Variation of lattice
parameter with composition of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The interplanar distance for each diffraction „hkl‟ planes were calculated using
Bragg‟s equation. The observed and calculated values of interplanar distances show good
agreement. The lattice parameter „a‟ was calculated for each plane from interplanar distance.
The Fig. 1b represents the variation of lattice parameter „a‟ with Mn substitution „x‟. It was
observed that the lattice parameter increases linearly with increasing Mn substitution in
accordance with the Vegard‟s law [8]. This behavior has been attributed to the replacement
of smaller Ni2+
ions (0.70 A
o) by larger Mn
2+ ions (0.81 A
o) in the crystal lattice. Thus, the
introduction of Mn2+
ions in lattice causes the expansion of unit cell while preserving the
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overall cubic symmetry. The lattice parameters of ferrite samples calculated from their XRD
patterns were found to be in the range 8.3821 Ao to 8.4632 A
o which are in agreement with
the reported values for Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites system [9]. The small
impurity peaks observed in the diffractograms are assigned to the α-Fe2O3 secondary phase.
The X-ray density decreases with increasing Mn substitution. This density behaviour is
attributed to the replacement of heavier NiO (6.72 g / cc) by the lighter MnO (5.37 g / cc) in
the spinel lattice. The average crystallite size was calculated from most intense XRD peaks
using Debye-Scherrer formula. The average crystallite size was observed in the range 22 nm
to 33 nm suggesting the nanocrystalline nature of these ferrites.
3.2. FTIR spectra of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The infrared spectroscopy is a very important technique to derive information about
the positions of ions in the crystal lattice through the crystal‟s vibration modes. The IR bands
in the region 700 cm-1
to 300 cm-1
are assigned to the fundamental vibrations of the ions of
the crystal lattice. The FTIR spectra of all Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites were
represented in the Fig. 2. All the ferrite samples display two principal absorption bands in the
frequency region from 4000 cm-1
to 400 cm-1
. The high frequency band (ν1) in the region
593 cm-1
to 563 cm-1
results from stretching vibration of the tetrahedral Fe3+
--O2-
bond, while
low frequency band (ν2) in the region 420 cm-1
to 400 cm-1
arises due to Fe3+
--O2-
stretching
vibration in octahedral sites [10]. The difference in the positions and intensities of ν1 and ν2
band are due to the different Fe3+
--O2−
distances for the tetrahedral and octahedral sites, since
the vibrational frequencies depend on cation mass, Mn+
--O2-
distance and the bonding force
[11].
Fig.2. FTIR spectra of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
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3.3. SEM of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The SEM was used to investigate into the size and shape and to confirm the
nanocrystalline nature of the Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites. The Fig. 3 represents
the SEM micrographs of the samples of above mentioned ferrite compositions. The ferrite
nanoparticles were polydispersed. These nanoparticles display low tendency towards
agglomeration and hence occur as loose agglomerates. The crystallite size calculated using
Scherrer method from XRD measurements was found to be in the range 22-33 nm.
Fig.3. SEM of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
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4. Studies on solid state properties of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
4.1. DC resistivity measurements
Spinel ferrites are known to exhibit semiconducting behaviour, though the mechanism
of conduction is different. The mechanism of electrical conductivity in ferrites involves
hopping of electrons between cations of same metal present in different oxidation states as
explained by the Verwey model [12]. According to this model, in close-packed lattice formed
by oxygen (anions), the metal ions occupy tetrahedral (A) sites and the octahedral [B] sites.
The cations at these A and B sites can be treated as isolated from each other. The electron
hopping at between two tetrahedral sites (A-A) does not take place since distance between
two tetrahedral sites is larger than the distance between two octahedral sites [B-B], hence the
hopping between the Fe2+
and Fe3+
ions occupying the octahedral [B] sites is primararily
responsible for conduction [13]. Besides electron hopping, other factors such as particle size,
grain boundaries, nature and concentration of other substituents present are known to affect
the conductivities of ferrites [14].
Fig.4. Plot of log resistivity against 103 / T of Ni0.6-xMnxZn0.4Fe2 O4 (x = 0.0-0.6) ferrites
In case of nanocrystalline ferrite materials, their resistivity was found to be affected
by moisture content which results from their high porosity and low green density [15]. The
temperature dependence of the dc resistivity (log ρ) for the Ni0.6-xMnxZn0.4Fe2 O4 (x = 0.0-0.6)
ferrite nanoparticles is shown in Fig.4. The plot displays two distinct regions of conductivity.
In the first region from room temperature to 393 K to 403 K resistivities of the order of 105
Ωcm to 107
Ωcm were observed depending upon the composition of the nanosize ferrites.
With increase in temperature in this region, the resistivity increases and reaches maximum in
the temperature range 373 K to 388 K. This behaviour is attributed to the presence of open
porosity, loose agglomeration and entrapped moisture inside the pores of the powders [16].
The heating from room temperature upto ~383K causes total evaporation of moisture from
the samples and therefore, maximum resistivities (ρ = 108 Ωcm to 10
9 Ωcm) were observed in
the temperature region 373 K to 388 K. The low resistivity at room temperature is resultant of
protonic conductivity due to entrapped moisture [17]. In the second region above 393 K, the
samples exhibits typical negative temperature coefficient of resistance (NTCR) behaviour of
ferrites [18] and linear plots were obtained.
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4.2. AC susceptibility studies of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The magnetic properties of materials are determined by the types of particles which
includes, single domain (SD), multidomain (MD) and superparamagnetic (SP) particles. The
ac susceptibility measurements can be used to find out the types of particles responsible for
magnetic properties. The variation of normalized ac susceptibility against temperature of
Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites is shown in Fig. 5a.
Fig.5. (a) Plot of normalised ac susceptibility against temperature of Ni0.6-xMnxZn0.4Fe2O4
(x=0.0-0.6) ferrites, (b) Variation of Curie temperature with composition of Ni0.6-
xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
These graphs show normal ferrimagnetic behaviour and the susceptibility suddenly
drops to zero at certain temperature, this temperature is called Curie temperature (Tc). The
nature of plots indicates that, the sample contains clusters of both single domain and
superparamagnetic particles. The variation of Curie temperature with composition of the
ferrite series under study is shown in the Fig.5b which can be correlated with the Mn2+
ions
concentration and A-B interactions. The decrease in Curie temperature with increasing
temperature suggests decrease of A-B interactions.
4.3. Dielectric studies of Ni0.6-xMnxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The dielectric properties of Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites were studied in
a frequency range from 100 Hz to 10 MHz at room temperature.
The frequency variation of dielectric constant of Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6)
ferrites at room temperature in the frequency range of 100 Hz to 10 MHz is presented in
Fig.6a. The dielectric constant (ε‟) shows sharp decrease upto 1 kHz, followed by a gradual
decrease from 1 kHz to 10 kHz, and is nearly independent of frequency from 10 kHz to 10
MHz.
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Fig.6. (a) Frequency variation of dielectric constant of Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6)
ferrites at room temperature, (b) Frequency variation of dielectric loss of Ni0.6-
xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites
The decrease in dielectric constant with increasing frequency is a normal behaviour
observed in most of the ferromagnetic materials. The dielectric constant of any material, in
general, is due to dipolar, electronic, ionic and interfacial polarizations [19]. In a lower
frequency region, surface polarization contributes predominantly than electronic or ionic
polarization in determining the dielectric properties of ferrite materials [20]. The dispersion
in dielectric constant observed in lower frequency region is due to Maxwell-Wagner
interfacial type of polarization [21] which is well in agreement with Koop‟s
phenomenological theory of dielectrics [22]. According to this model, the dielectric structure
is assumed to be composed of two layers; the first layer is composed of well conducting
grains separated by thin layer which is composed of relatively poor conducting grain
boundaries. This creates inhomogeniety in the dielectric material which results in local
accumulation of charge under the influence of an electric field. The electrons reach the grain
boundary through hopping and if the grain boundary resistance is high enough, the electrons
pile up at the grain boundaries and produce polarization. However, as the frequency of the
applied field is increased, the electrons reverse their direction of motion more often. This
decreases the probability of electrons reaching the grain boundary and as a result the
polarization decreases. Therefore, the dielectric constant decreases with increasing frequency
of the applied field. The dielectric constant values are quite low and are in the range of 30 to
450 at room temperature. These low dielectric constant values are attributed to homogeneity,
better symmetry and small grain size [23]. Small grains have large surface boundaries which
act as scattering centres for the flow of electrons thus reducing the interfacial polarization
[24]. The variation of dielectric loss (tan δ) with frequency at room temperature is depicted in
the Fig. 6b. It was observed that dielectric loss decreases initially with frequency. The
dielectric loss in ferrite materials depend on a number of factors such as stoichiometry, Fe2+
concentration and structural homogeneity which in turn depend on the composition and
method of preparation. The dielectric loss gives the loss of energy from the applied field into
the sample. This is caused by domain wall resonance. At higher frequencies, the losses are
found to be low, since domain wall motion is inhibited and magnetization is forced to change
rotation. The initial decreased can be understood from Koop‟s phenomenological model [22].
The dielectric loss of Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites was found to very low in the
higher frequency region.
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4.4. Summary
The work incorporated in project involves synthesis, characterization and studies on
the electrical, magnetic and dielectric properties Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites.
The ferrite materials were synthesized using combustion technique involving hexamine and
metal nitrate mixture. The single phase formation of Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6)
ferrites was confirmed by the XRD measurements wherein all the XRD peaks characteristics
of cubic spinel ferrite were observed. The small impurity peaks observed in the
diffractograms are assigned to the α-Fe2O3 secondary phase. The lattice parameters of all
ferrites were found to increase gradually with increasing Mn substitution. The peak
broadening observed for these ferrites indicates their nanocrystalline nature. The FTIR
spectra of ferrites display two absorption bands which are chracteristics of M---O stretching
in tetrahedral and octahedral sites in the spinel lattice. The SEM observations shows that the
consists of loose agglomerates of primary particles.
The Mn substitution has sigificant influence on the electromagnetic properties such as
dc resistivity, dielectric constant, dielectric loss tangent etc. The lower dc resistivity values in
the range 106 Ωcm to 10
7 Ωcm observed for Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites at
room temperature suggest the protonic conductivity due to moisture trapped inside the pores.
The ac susceptibility studies reveal the presence of clusters of both superparamagnetic and
single domain particles in ferrites. The Curie temperature was found to decrease with
increasing Mn concentration which is due to the decrease A-B sublattice interaction. The
decrease A-B sublattice interaction suggests the transfer of Fe3+
from A-site to B-site with
increasing Mn content. The dielectric constant values are quite low and are in the range of 30
to 450 at room temperature. These low dielectric constant values are attributed to
homogeneity, better symmetry and small grain size. Small grains have large surface
boundaries which act as scattering centres for the flow of electrons thus reducing the
interfacial polarization. The dielectric loss of ferrites was found to very low in the higher
frequency region.
4.5. Conclusions
The present investigation was focused on synthesis, characterization and solid state
properties of Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites. The significant findings of this
investigation are as follows:
1. Nanocrystalline Ni0.6-xMnxZn0.4Fe2O4 (x = 0.0-0.6) ferrites were successfully synthesized
using combustion technique involving hexamine and metal nitrate mixture. The
temperature and time of preparation were reduced as compared to the conventional solid
state process.
2. The XRD studies indicate formation of cubic spinel ferrites with lattice parameters in the
range 8.3821 Ao to 8.4632 A
o.
3. The FTIR spectra displays two principal absorption bands in the region 593 cm-1
to 563
cm-1
and 420 cm-1
to 400 cm-1
which arises due to Fe3+
--O2-
stretching vibration in
tetrahedral and octahedral sites respectively.
4. The low values dc resistivity observed at room temperature are attributed to the protonic
conductivities due to entrapped moisture in the porous structure of the ferrites. The
resistivity decreases with increasing Mn substitution at higher temperatures.
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5. The Curie temperature was found decrease with increasing Mn substitution indicating the
decrease in the A-B sublattice interactions.
6. The dielectric constant and dielectric loss tangent values are appreciably lower than those
reported for samples prepared by solid state processes.
5. Characterization of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
5.1. XRD pattern of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The XRD patterns of all the Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6)
ferrites are presented in Fig.7a. The X-ray diffractograms displays all the peaks
characteristics of the cubic spinel ferrites with no detectable secondary phases which confirm
the formation and purity of these ferrite samples. This reveals that the Cu substituted Ni-Zn
ferrites can be directly synthesized from the auto-combustion of hexamine-nitrate mixture.
Fig.7 (a) XRD pattern of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites, (b) Variation of lattice
parameter and density with composition of Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites
The XRD peaks show broadening which is indicative of the ultrafine
(nanocrystalline) nature of all Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites. The interplanar
distances for each diffraction „hkl‟ planes were calculated using Bragg‟s equation. The
observed and calculated values of interplanar distances show good agreement. The lattice
parameter „a‟ was calculated for each plane from interplanar distance. The Fig. 7b represents
the variation of lattice parameter „a‟ with Cu substitution „x‟. It was observed that the lattice
parameter increases linearly with increasing Cu substitution in accordance with the Vegard‟s
law [8]. This behavior has been attributed to the replacement of smaller Ni2+
ions (0.70 A
o)
by larger Cu2+
ions (0.73 Ao) in the crystal lattice. Thus, the introduction of Cu
2+ ions in
lattice causes the expansion of unit cell while preserving the overall cubic symmetry. The
lattice parameters of ferrite samples calculated from their XRD patterns were found to be in
the range 8.3821 Ao to 8.4046 A
o. The X-ray density increases with increasing Cu
substitution. This density behaviour is attributed to the replacement of lighter NiO by the
heavier CuO in the spinel lattice. The average crystallite size was calculated from most
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intense XRD peaks using Debye-Scherrer formula . The average crystallite size was observed
in the range 22 nm to 30 nm suggesting the nanocrystalline nature of these ferrites.
5.2. FTIR spectra of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The infrared spectroscopy is a very important technique to derive information about
the positions of ions in the crystal lattice through the crystal‟s vibration modes. The IR bands
in the region 700 cm-1
to 300 cm-1
are assigned to the fundamental vibrations of the ions of
the crystal lattice. The FTIR spectra of all Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites were
represented in the Fig. 8. All the ferrite samples display two principal absorption bands in the
frequency region from 4000 cm-1
to 400 cm-1
. The high frequency band (ν1) in the region
593 cm-1
to 563 cm-1
results from stretching vibration of the tetrahedral Fe3+
--O2-
bond, while
low frequency band (ν2) in the region 420 cm-1
to 400 cm-1
arises due to Fe3+
--O2-
stretching
vibration in octahedral sites [10]. The difference in the positions and intensities of ν1 and ν2
band are due to the different Fe3+
--O2−
distances for the tetrahedral and octahedral sites, since
the vibrational frequencies depend on cation mass, Mn+
--O2-
distance and the bonding force
[11].
Fig.8. FTIR spectra of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
5.3. SEM of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The SEM was used to investigate into the size and shape and to confirm the
nanocrystalline nature of the Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites. The Fig. 9 represents
the SEM micrographs of the samples of above mentioned ferrite compositions. The ferrite
nanoparticles were polydispersed. These nanoparticles display low tendency towards
agglomeration and hence occur as loose agglomerates. The crystallite size calculated using
Scherrer method from XRD measurements was found to be in the range 22-28 nm.
Page 15
Fig.9. SEM of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
6. Studies on solid state properties of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
6.1. Dc resistivity measurements
Spinel ferrites are known to exhibit semiconducting behaviour, though the mechanism
of conduction is different. The mechanism of electrical conductivity in ferrites involves
hopping of electrons between cations of same metal present in different oxidation states as
explained by the Verwey model [12]. According to this model, in close-packed lattice formed
by oxygen (anions), the metal ions occupy tetrahedral (A) sites and the octahedral [B] sites.
The cations at these A and B sites can be treated as isolated from each other. The electron
hopping at between two tetrahedral sites (A-A) does not take place since distance between
Page 16
two tetrahedral sites is larger than the distance between two octahedral sites [B-B], hence the
hopping between the Fe2+
and Fe3+
ions occupying the octahedral [B] sites is primararily
responsible for conduction [13]. Besides electron hopping, other factors such as particle size,
grain boundaries, nature and concentration of other substituents present are known to affect
the conductivities of ferrites [14]. In case of nanocrystalline ferrite materials, their resistivity
was found to be affected by moisture content which results from their high porosity and low
green density [15]. The variation of DC resistivity ( log ) versus 103/ temperature shown in
Fig.10. Linear decrease in the resistivity of ferrites with temperature shows their
semiconducting nature. The resistivity of ferrites is known to depend upon the purity starting
materials, sintering temperature and sintering time, which influence the microstructure and
composition of the samples. The plot displays two distinct regions of conductivity. In the first
region from room temperature to 393 K to 403 K resistivities of the order of 105 Ωcm to 10
7
Ωcm were observed depending upon the composition of the nanosize ferrites. With increase
in temperature in this region, the resistivity increases and reaches maximum in the
temperature range 373 K to 388 K. This behaviour is attributed to the presence of open
porosity, loose agglomeration and entrapped moisture inside the pores of the powders [16].
The heating from room temperature upto ~383K causes total evaporation of moisture from
the samples and therefore, maximum resistivities (ρ = 108 Ωcm to 10
9 Ωcm) were observed in
the temperature region 373 K to 388 K. The low resistivity at room temperature is resultant of
protonic conductivity due to entrapped moisture [17]. In the second region above 393 K
(Fig.10), the samples exhibits typical negative temperature coefficient of resistance (NTCR)
behaviour of ferrites [18] and linear plots were obtained. The variation of room-temperature
resistivity with Cu content indicates that resistivity decreases with increase in Cu content
(except x=0.4). The decrease in resistivity is attributed to the increase in grain size. Smaller
grains also imply smaller grain to grain contacts, which reduces the electron flow. As the
crystallite size increases (with increase in Cu content) the resistivity is found to decrease.
Fig.10. Plot of log resistivity against 103 / T of Ni0.6-xCuxZn0.4Fe2 O4 (x = 0.0-0.6) ferrites
Page 17
6.2. AC susceptibility studies of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The magnetic properties of materials are determined by the types of particles which
includes, single domain (SD), multidomain (MD) and superparamagnetic (SP) particles. The
ac susceptibility measurements can be used to find out the types of particles responsible for
magnetic properties. The variation of normalized ac susceptibility against temperature of
Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites is shown in Fig. 11a. These graphs show normal
ferrimagnetic behaviour and the susceptibility suddenly drops to zero at certain temperature,
this temperature is called Curie temperature (Tc). The nature of plots indicates that, the
sample contains clusters of both single domain and superparamagnetic particles. The
variation of Curie temperature with composition of the ferrite series under study is shown in
the Fig. 11b which can be correlated with the Cu2+
ions concentration and A-B interactions.
The decrease in Curie temperature with increasing temperature suggests decrease of A-B
interactions.
Fig. 11a. Plot of normalized ac susceptibility plot of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
(b) Variation of Curie temperature with composition of Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6)
6.3. Dielectric studies of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites
The dielectric properties of Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites were studied in
a frequency range from 100 Hz to 10 MHz at room temperature.
The frequency variation of dielectric constant of Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6)
ferrites at room temperature in the frequency range of 100 Hz to 10 MHz is presented in
Fig.12a. The dielectric constant (ε‟) shows sharp decrease upto 1 kHz, followed by a gradual
decrease from 1 kHz to 10 kHz, and is nearly independent of frequency from 10 kHz to 10
MHz. The dielectric constant of any material, in general, is due to dipolar, electronic, ionic
and interfacial polarizations [19]. In a lower frequency region, surface polarization
contributes predominantly than electronic or ionic polarization in determining the dielectric
properties of ferrite materials [20]. The decrease in dielectric constant with increasing
frequency is a normal behaviour observed in most of the ferromagnetic materials. The high
Page 18
value of dielectric constant observed at lower frequencies is explained on the basis of space
charge polarization due to in homogeneous dielectric structure. The inhomogeneities in
ferrites are impurities, porosity and grain size [21]. Also, the polarization in the ferrites is
through a mechanism similar to the conduction process. The presence of Fe3+
and Fe2+
ions
render ferrite materials dipolar. The rotational displacement of dipoles results in orientational
polarization. In ferrites, rotation of Fe2+
to Fe3+
can be visualized as the exchange of electrons
between two ions, so that the dipoles align themselves in response to alternating electric field.
The polarization at lower frequencies may result from electron hopping between Fe3+
and
Fe2+
ions in ferrite lattice. The polarization decreases with increase in frequency and reaches
a constant value due to the fact that beyond a certain frequency of external field the electron
exchange Fe3+
and Fe2+
cannot follow the alternating field. Also, the presence of Ni3+
/ Ni2+
ions, which gives rise to p-type carriers, contributes to net polarization, though it is small.
The net polarization increases initially and then decreases with decrease in frequency [22].
Fig.12(a). Frequency variation of dielectric constant of Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6)
ferrites at room temperature (b) Frequency variation of dielectric loss at room temperature of
Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites
The dielectric constant values in the higher frequency region are quite low and are in
the range of 14 to 54 at room temperature. These low dielectric constant values are attributed
to homogeneity, better symmetry and small grain size [23]. The mechanism of conduction in
polycrystalline ferrites is mainly reported to be hopping of electrons between ions of the same
element having different oxidation states. As these ferrites are not sintered, the probability of
ion existing in different valance states is rather low, reducing the possibility of electron
hopping and hence, the polarization which results in low dielectric constant. It is also affected
by stoichiometry, density, grain size and homogeneity of the ferrites [24]. As Cu2+
ions are
substituted for Ni2+
ions, the change in structural homogeneity results in the increase of
polarization which results in the increase of dielectric constant. The variation of dielectric
loss (tan δ) with frequency at room temperature is depicted in the Fig. 12b. It was observed
that dielectric loss decreases initially with frequency. The dielectric loss in ferrite materials
depend on a number of factors such as stoichiometry, Fe2+
concentration and structural
homogeneity which in turn depend on the composition and method of preparation. The
dielectric loss gives the loss of energy from the applied field into the sample. This is caused
by domain wall resonance. At higher frequencies, the losses are found to be low, since
Page 19
domain wall motion is inhibited and magnetization is forced to change rotation. The initial
decreased can be understood from Koop‟s phenomenological model [22]. The dielectric loss
of Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites was found to very low in the higher frequency
region.
6.4. Summary
The experimental studies reported in this project involves synthesis, characterization
and studies on the electrical, magnetic and dielectric properties Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-
0.6) ferrites. The Cu-substituted Ni-Zn ferrites were synthesized using combustion technique
involving hexamine and metal nitrate mixture. The single phase formation of Ni0.6-
xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites was confirmed by the XRD measurements wherein all
the XRD peaks characteristics of cubic spinel ferrite were observed. The lattice parameters
shows gradual increase with increasing Cu concentration. The peak broadening of XRD
peaks is indicative of their nanocrystalline nature. The FTIR spectra of ferrites display two
absorption bands which are chracteristics of M---O stretching in tetrahedral and octahedral
sites in the spinel lattice. The SEM observations shows that the particle occurs as loose
agglomerates of primary particles.
The substitution of Cu has sigificant influence on the electromagnetic properties of
Ni-Zn ferrites. The lower dc resistivity values in the range 106 Ωcm to 10
7 Ωcm observed for
Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites at room temperature suggest the protonic
conductivity due to moisture trapped inside the pores. The ac susceptibility studies reveal the
presence of clusters of both superparamagnetic and single domain particles in ferrites. The
Curie temperature was found to decrease with increasing Cu concentration which is due to
the decrease A-B sublattice interaction. The decrease A-B sublattice interaction suggests the
transfer of Fe3+
from A-site to B-site with increasing Cu content. The dielectric constant
values are quite low and are in the range of 14 to 54 at room temperature. These low
dielectric constant values are attributed to homogeneity, better symmetry and small grain
size. Small grains have large surface boundaries which act as scattering centres for the flow
of electrons thus reducing the interfacial polarization. The dielectric loss of all ferrite samples
was found to very low in the higher frequency region.
6.5. Conclusions
The present investigation was focused on synthesis, characterization and solid state
properties of Ni0.6-xCuxZn0.4Fe2O4 (x=0.0-0.6) ferrites. The significant findings of this
investigation are as follows:
1. Nanocrystalline Ni0.6-xCuxZn0.4Fe2O4 (x = 0.0-0.6) ferrites were successfully prepared
using combustion technique involving hexamine and metal nitrate mixture. The
temperature and time of preparation were reduced as compared to the conventional solid
state process.
2. The XRD studies indicate formation of cubic spinel ferrites with lattice parameters in the
range 8.3821 Ao to 8.4046 A
o.
Page 20
3. The FTIR spectra displays two principal absorption bands in the region 593 cm-1
to 563
cm-1
and 420 cm-1
to 400 cm-1
which arises due to Fe3+
--O2-
stretching vibration in
tetrahedral and octahedral sites respectively.
4. The low values dc resistivity observed at room temperature are attributed to the protonic
conductivities due to entrapped moisture in the porous structure of the ferrites. The
resistivity decreases with increasing Cu substitution at higher temperatures.
5. The Curie temperature was found decrease with increasing Cu substitution indicating the
decrease in the A-B sublattice interactions.
6. The dielectric constant and dielectric loss tangent values are appreciably lower than those
reported for samples prepared by solid state processes.
Overall summary
Effect of
substitution
of R on Ni-
Zn ferrite
(R=Cu,Mn)
Parameter Cu Mn
Lattice constant increases increases
X-ray density increases decreases
DC resistivity decreases decreases
Curie temperature decreases decreases
Dielectric constant decreases (except x=0.4) decreases
Dielectric loss decreases decreases
Finally, from the overall results observed in the present study it can be concluded that
with combustion technique involving hexamine and metal nitrate mixture, it is possible to
prepare the nanocrystalline ferrites at relatively lower temperature and in much shorter time
duration than that require in the conventional solid state technique.
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Publications in Conferences/symposium
1. Vasudev Gawade, Saju Konadkar, Pooja Halarnkar, Mandali Borkar, Aarti
Chaudhary and U.B. Gawas, “Effect of substitution of Cu and Mn on structural and
solid state properties of Ni-Zn ferrite nanoparticles” in 1-day symposium, organized
by Department of Chemistry, Goa-University on 15th
March 2014. (Oral presentation)
2. M.M. Kothawale, R.M. Pednekar and U.B. Gawas „Structural, magnetic and dielectric
characteristics of nano crystalline Mn-Ni-Zn ferrites synthesized by combustion route‟ in 1-
day National Conference on Emerging Trend in Chemistry and Material Science,
organized by Department of chemistry, KLS Gogte institute of Technology, Belgaum,
Karnataka, 13th
Oct. 2014. (Oral presentation)
3. U.B. Gawas, S.G. Gawas and V.M.S. Verenkar, „Effect of Cu-substitution on structural,
dielectric and magnetic properties of Ni-Zn ferrite nanoparticles‟ in 1-day National
Conference on Emerging Trend in Chemistry and Material Science, organized by
Department of Chemistry, KLS Gogte institute of Technology, Belgaum, Karnataka,
13th
Oct. 2014. (Oral presentation)