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Hydrothermal Synthesis of NiFe2O4 nano-particles: Structural,
Morphological, Optical, Electrical and Magnetic Properties
K. Chandra Babu Naidu and W. Madhuri*
Ceramic Composites Laboratory, Centre for Crystal Growth, SAS, VIT University,
Vellore-632014, Tamilnadu, India.
Abstract
NiFe2O4 nano-crystallites with an average diameter of 8.9 nm are synthesized via
hydrothermal method. The single phase spinel structure is confirmed from X-ray
diffractograms. Morphology is analyzed by transmission and field emission scanning
electron microscopes. High specific surface area of 55.7 m2/g is obtained for nanoparticles. The M-H loop and M-T curve behavior is investigated by vibrating sample
magnetometer. The optical band gap energy is estimated from UV-Visible spectrum. In
addition, the frequency dependence of dielectric properties is investigated. Cole-Cole
plots are drawn to study electrical conduction mechanism and the kind of relaxation –
Debye or non-Debye type. Low ac-conductivity and low magnetic losses are noticed at 5
MHz frequency which is suitable for microwave device applications.
Keywords: Nano Materials; Transmission Electron Microscope; Dielectric Constant;
Permeability; Magnetic Properties.
________________________________________________________________________
*Corresponding author Email: [email protected]
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1. Introduction
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Nano ferrites are the promising materials for microwave device, magnetic resonance
imaging (MRI), catalysis, magnetic recording, microwave absorber, biosensors,
biomedical drug delivery, power transformers and telecommunication applications due to
their high thermal stability, enhanced electrical, optical and magnetic properties when
compared with bulk materials [1-4]. Nano nickel ferrite is a mixed spinel ferrite having
cation distribution of [Ni2+Fe3+]A[Ni2+Fe3+]B [5]. Many researchers have successfully
synthesized NiFe2O4 nano-particles by various techniques such as co-precipitation [6]
green nano-technology [7], sol-gel [8], reactive milling [9], solvothermal [10] and eggwhite precursor [11] methods in order to investigate the structural, optical, morphological,
electrical and magnetic properties. But hydrothermal method offers many advantages
over the rest of methods such as low cost for sample preparation, high crystallinity,
simplicity and usage of low temperatures. In this investigation additionally dielectric
properties, impedance spectroscopic analysis and magnetic permeability properties are
explored for as synthesized nano-particles which have not been reported earlier by
hydrothermal technique.
2. Experimental Procedure
In order to synthesize NiFe2O4 nano-particles Ni (NO3)2 6H2O, Fe (NO3)3 9H2O (each
of 99.8 % purity, Sigma Aldrich) and NaOH are taken as precursors. Deionized water is
used as a solvent. Nickel and iron nitrates are dissolved in distilled water by maintaining
the ratio of nitrates (gm): water (ml) as 1:3. The resultant solution is stirred until it gets
converted into nano-particles. NaOH (gm) is added little by little to the solution (ml) in
1:4 (NaOH: nitrates) ratio. The PH of 11 is maintained to the mixture to achieve pure
spinel phases. Furthermore, the mixture is vigorously stirred for 2hr and transferred into a
300ml Teflon-lined steel autoclave. The sealed autoclave is heat treated at 1500C for
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48hr. After 48hrs the autoclave is slowly cooled to room temperature. The precursor in
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the autoclave is filtered, washed with acetone and distilled water for number of times till
PH is decreased to 7. Later nickel ferrite nano-particles are separated from autoclave and
dried at 600C for 6hr. The synthesis part is depicted in Fig.1. The as prepared powder is
characterized using X-ray diffractometer (Bruker X-Ray Powder Diffraction Meter, CuKα,
λ=0.15418nm), Field-emission Scanning Electron Microscope (Ultra 55 FE-SEM Carl
Zeiss), Transmission Electron Microscope (TEM: Model Tecnai G20, FEI, USA), JASCO
UV-Visible spectrophotometer (V-670 PC), FT-IR spectrophotometer (IR affinity-1,
Shimadzu), HIOKI 3532-50 LCR controller (Japan) and Vibrating Sample Magnetometer
(EV-7 VSM with Max. applied field +15kOe.) for structural, morphological, optical,
electrical and magnetic properties respectively.
3. Results and Discussions
3.1Structural analysis
Fig.2 (a) depicts the variation of intensity as a function of two theta angle (2θ) from
100 and 800 for NiFe2O4 nano-particles. The diffractogram pattern of as prepared sample
exhibited single phase formation of face centered cubic structure with high crystallinity.
The location of Bragg lines with reflections from the planes of (111), (220), (311), (222),
(400), (422), (511), (440), (620), (533), (622) and (444) are in good agreement with
standard JCPDS: 86-2267. The locations of main peaks are used to find inter-planar
spacing (d) of Bragg’s lines. No secondary phases are noticed in spectra. Thus, the
obtained nickel ferrite nano particles are highly pure in phase. The average crystallite size
‘D’ (8.9nm) is determined from average full width half maxima (FWHM) of all reflection
peaks using Debye-Scherrer formula [12].
0.9λ
D = = 𝛽𝐶𝑜𝑠θ ____________ (1)
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where β is FWHM, λ is wave length of CuKα source (0.1542nm) and θ is diffraction angle.
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Williamson-Hall (W-H) plot (as shown in Fig.2 (b)) is drawn for βcosθ versus 4sinθ in order
to evaluate micro-strain (ε) and crystallite size (D) using following relation [13].
β Cosθ =
0.9λ
𝐷
+ 4ε Sinθ ___________ (2)
where slope of straight line offers micro-strain while crystallite size is associated to intercept
parameter. This gives correlation between ‘ε’ and ‘D’ values. The results are mentioned in
Table.1.The lattice constants (a, b & c) are computed from inter-planar spacing and miller
indices (hkl). The achieved value of ‘a’ (0.833nm) is almost equal to the reported data [13].
X-ray density (5.393g/cm3) of nano particles is calculated from the relation Dx = ZM/Na3,
where ‘Z’ is the no. of molecules per unit cell (Z=8), ‘M’ is the molecular weight of the
composition, ‘N’ is Avogadro’s number (6.023 x 1023) and ‘a’ is the lattice parameter.
Moreover, few structural parameters such as Scherrer strain (ε*) and dislocation density (ρd)
are calculated using the following relations [14] and are presented in Table.1.
β
1
ε* = 4𝑡𝑎𝑛θ _________ (3) ρd = 𝐷2 ____________ (4)
3.2 Surface Morphology
Fig.3 (a) shows the TEM images of nickel ferrite nano particles. The average particle
size (D') of prepared sample is about 20nm. The obtained nickel ferrite particle size is much
smaller than the reported value170nm by Wang et.al, solvothermal technique (1800C/48hr)
[15]. The reduction of particle size is attributed due to lowering the annealing temperature in
hydrothermal method (1500C/48hr). The surface area (S) is a physical property of nano
materials. This has got more importance than its bulk counter part due to nano ordered grain
size. Basically, nano materials will have large ‘S’ value while bulk materials will have small
value. Magnetic properties of ferrites are very sensitive to the surface area [16]. The surface
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area obtained for the present nano ferrite, 55.7m2/g is very large as calculated form TEM
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studies using the following relation.
S=
6
𝐷′𝜌𝑥
_________ (5)
The magnetic interaction between nano-particles is responsible for the weak agglomeration in
TEM photographs [16]. The selected area electron diffraction (SAED) indicates the wellcrystalline nature of single phase nano NiFe2O4 (Fig.3 (b)). The SAED pattern is indexed by
(311), (400), (511) and (440) planes and is in agreement with diffraction data. The FE-SEM
photographs and EDS spectra including compositional data of as synthesized NiFe2O4 powder
samples are shown in Fig.4. Diamond cube like grains are identified. Average grain size (Ga)
is found to be of order 57.9nm using linear intercept method and is given by
G=
1.5 L
MN
___________ (6)
Where L=the total test line length, M=the magnification, N=the total number of intercepts
which the grain boundary makes with the line. EDS attributes the inhibited elements and
impurities in the samples with their At% and Wt%. No impurities are noticed in the EDS
spectrum once again confirming that the synthesized nickel ferrite nano particles are pure in
nature.
3.3 UV-Visible spectra
The diffuse reflectance spectrum is recorded in the range of 200-1500 nm for
evaluating optical band gap of powder samples. Kubelka- Munk function of reflectance F(r)
is used to determine band gap [17].
F(r) =
(1−𝑟)2
2𝑟
_____________ (7)
The absorption coefficient (α) is directly proportional to F(r) and hence an equation to find
band gap can be written as follows.
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(αhν)n = m (hν- Eg) _________ (8)
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Where m= Energy- independent constant that depends on transition probability, Eg= optical
band gap energy, n= the kind of transition i.e. n = 2 for direct transition, 2/3 for direct
forbidden transition, ½ for indirect transition, 1/3 for indirect forbidden transition and hν =
photon energy [18]. In this study n= 2 is taken for direct transition. Eg value is considered as
the extrapolated tangent value towards X-axis for (αhν)2 versus photon energy hν (eV) plot as
α tends to zero (Fig.5). The band gaps of bulk (microwave sintered at 10000C) and nano
NiFe2O4 (NF) samples are calculated as 1.45 eV and 1.57 eV respectively. The obtained Eg of
nano NF is in consistent with the reported value of 1.56 eV [19]. Grain size variation and
specific surface area are responsible for variation of band gaps of bulk and nano ferrites. It is
a known fact that the number of oxygen vacancies increase with decrease of grain size [19]
i.e. nano nickel ferrites (high surface area) possess more number of oxygen vacancies than its
bulk (low surface area). Indeed, these oxygen vacancies act as electron (e-) trapping centers
and play a key role in hindering the recombination rate of photo induced charge carriers (e-&
h) intensifying photo-catalytic activity of ferrites [20]. However, more number of oxygen
vacancies is created in nano NiFe2O4 and could be able to trap more number of carriers
leading to the reduction of electron-hole (e--h) separation efficiency. Thus enhances the photo
catalytic activity of nano ferrite powders.
3.4 FT-IR spectra
FT-IR absorption spectrum in the range of 4000-400 cm-1 of as-prepared NiFe2O4
(NF) nano particles is depicted in Fig.6.Two kinds of metal-oxide (M-O) absorption bands
are detected in the range of 400-590 cm-1 confirming the formation of spinel nickel ferrite.
The bands at wave numbers 449.5 cm-1, 583.4 cm-1, 1364.3 cm-1, 1628.2 cm-1, 2849.1 cm-1,
2926.4 cm-1 and 3432.3 cm-1 appeared in FTIR spectrum of nano ferrite sample. The first and
second absorption bands around 449.5cm-1 (ν1) and 583.4cm-1 (ν2) [21, 22] are associated to
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metal oxide (Ni-O and Fe-O) stretching vibrations at octahedral B-site and Fe-O stretching
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vibrations at tetrahedral A-site respectively [23]. The peak at 1364.3 cm-1 shows bending
vibrations of O-H which are assigned to OH- absorbed by ferrites [22]. Few absorption bands
occurred at 2849.1 cm-1 and 2926.4 cm-1are due to intra-molecular stretching modes that arise
from different proportions of hydrogen bonding within the frame work of tetrahedral bonded
structure [24].The detected bands at 1628.2 and 3432.3 cm-1 are due to O-H stretching and
bending vibrations of H2O molecules absorbed by nano ferrites respectively [22, 23]. The
force constants of both A-site (Kt = 60.79 N/m) and B-site (Ko = 25.15 N/m) are obtained by
employing Waldron method [25]. Mathematically, it is represented by
Kt= 7.62 x Mt x 𝜈𝑡 2 x 10-7 (N/m) ___________________ (9)
Ko= 5.31 x Mo x 𝜈𝑜 2 x 10-7 (N/m) __________________ (10)
where Mt and Mo are the molecular weights of cations at tetrahedral and octahedral sites
respectively.
3.4 Electrical Properties
The frequency dependence of real and imaginary part of complex permittivity (ε* =
ε'- j ε") is shown in Fig.7 (a). The ε' and ε" are referred as dielectric constant and dielectric
loss respectively. It can be seen from Fig.7 (a) that ε' and ε" achieve higher values at lower
frequencies and decreasing with increasing frequency. The Maxwell-Wagner interfacial
polarization is responsible for attaining high ε' and ε" values at lower frequencies [26].
According to this theory ferrimagnetic materials are assumed to have larger grains and
smaller grain boundaries as conducting and insulating layers respectively. Grain boundaries
exhibit faster response to the input ac-frequency at low frequencies causing an increase in
polarization. Hence, more number of ferrous (Fe2+) ions is generated during the hopping
mechanism. Since, hopping of carriers at the localized sites is universal in Maxwell- Wagner
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double layer model. Thus, ε', ε" and tanδ (dissipation factor) values increase as shown in
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Fig.7 (a) & (b). Moreover, grains are more active at high frequencies and lead to dielectric
dispersion above certain critical frequencies. At these frequencies, the electron exchange
oscillations between Fe3+ and Fe2+ ions can’t follow the applied ac-frequency. This lowers the
values of dielectric parameters at higher frequencies. Quality factor (Q x f) is the reciprocal
of loss tangent and is increasing with frequency. A slight knick observed in the loss tangent
plot at higher frequencies must be due to the collective contribution of electrons and holes
[27] at the interfacial boundary layer. In case of as synthesized nickel ferrite (NF) nanoparticles low dielectric constant and low losses are obtained at high frequencies due to high
specific surface area (S) [28]. This high ‘S’ value is usually achieved owing to the smallest
particle size (of nm range) of sample. The values of few dielectric parameters at 5 MHz
frequency are shown in Table.2.
The frequency dependence of ac-conductivity is shown in Fig.8. It can be observed
that the conductivity is increasing exponentially with increase of frequency up to 2.5 MHz.
This happens due to sustained hopping of electrons between ferrous and ferric ions at
octahedral sites [27]. After 4 MHz frequency a sharp drop off of conductivity is noticed. It
may be due to unavailability of ferrous ions at octal position i.e., hopping rate of electrons is
decreased [27]. At 5 MHz the achieved σac value is 3.82x10-6 S/cm which is lower than the
reported value (1.7x10-4, ~8 x 10-6& ~1.25 x 10-5 S/cm) for NF nano-crystallites prepared by
egg-white precursor, citrate-gel and co-precipitation method respectively [27-29].
The dc-conductivity is evaluated from power law fit to the plot as per the following
equation:
σac (ω, T) = σdc (T) + Bωn (ω) ____________ (11)
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where σdc is dc-conductivity, B is constant, n is exponent and ω = 2πf. In Fig.8 the frequency
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independent portion (between 2.5 MHz -4 MHz) is extrapolated towards Y-axis. Thus, the
intersecting point establishes σdc of 5.9 x 10-6 S/cm, whereas the exponent (n) value equals to
0.156.The n value is in good agreement with reported one by sol-gel auto-combustion method
[30].
3.5 Impedance analysis
Impedance spectroscopic studies are useful for investigating the electrical properties
of ferrites and will give information about grains and grain boundaries. In accordance with
Maxwell- Wagner double layer model, the grains are considered to be high conducting layers
while grain boundaries are treated as low conducting layer. Fig.9 depicts the Cole-Cole plot
(Z' Vs. Z") of NiFe2O4 (NF) nano-particles at room temperature (RT). The electron exchange
between nickel and iron ions is responsible for the conduction mechanism in Nyquist plot. In
this investigation cole-cole plot shows two semicircular arcs within the complex plane. The
first one is formed due to interfacial boundary (grain boundary) conduction at lower
frequencies while the latter is due the conduction through bulk crystals (grains) at high
frequencies [31, 32]. The centers of arcs lie below the real axis. So, it indicates the spread of
relaxation with different (mean) time constant and hence confirms the non-Debye type
relaxation mechanism [32]. The obtained total bulk conductivity of NF is (1.29 x 10-6 S/cm)
in agreement with dc-conductivity (3.82 x 10-6 S/cm) achieved from ac-conductivity versus
frequency plot (Fig. 8). The values are higher than reported value of 1.31x10-8 S/cm at RT
[33]. Therefore, this result also confirms the semi-conducting nature of material. It happens
owing to the contribution of conductivity of grain and grain boundary. The impedance is
generally evaluated by an equivalent circuit of two parallel RC-elements connected in series.
With the help of Z-view software, RC-elements are acquired to be R1 = 0.13 MΩ, R2 = 0.25
MΩ, C1 = 5.09pF and C2 =1.04nF. The corresponding relaxation times (τ1 = R1C1& τ2 =
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R2C2) are evaluated. From the obtained results the relaxation time of grain (τ1 = 0.65μs) is
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smaller than its boundary value (τ2 = 256.5μs). Since the semicircle of grain stays at higher
frequencies while interfacial boundary lies at lower frequencies (i.e. τ = 1/ω).
The complex electric modulus (M*) is an indication of the extent of dielectric spacecharge relaxation. The electric modulus is represented as M* =M' + jM" and can be
calculated using following relations:
M' =
𝜀′
ε′2 + ε"
_______ (12) M" =
2
𝜀"
ε′2 + ε"2
____________ (13)
Room temperature electric modulus spectrum (M' Vs M") is carried out from 50Hz – 5MHz
frequency. In Fig.10, two prominent semicircular arcs are noticed and the centers of arcs lie
below the real axis. Hence, it is confirmed that the non-Debye type dielectric relaxation is
assigned to the present NF [32].
3.6 Magnetic Properties
Fig.11 shows the frequency dependence of initial permeability (μ') and magnetic loss (μ")
of toroidal shaped nano NF. These are calculated using the following relation:
𝐿
𝑠
µ' = (0.004606N2 h log10
(Do/Di)) µH
μ" = μ' tanδ
___________ (14)
___________ (15)
Where N = no. of copper coil turns on the toroid (28 in this case), h = thickness of toroid
(inches), Do, Di are outer and inner diameters (inches), Ls= series inductance in µH [34]. It
can be seen that the permeability is increasing with increase of frequency up to 0.4 MHz. For
further increase of frequency μ' is decreasing towards lower values due to resonance
behavior. As the applied field frequency matches with the precision frequency of dipoles
some amount of energy is propagated to the spinning dipoles from input filed. Therefore, μ'
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reaches maximum value at resonance frequency (fr). Above fr, μ' obeys the Snoek’s law as fr
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α 1/ (μ'-1) [35]. The occurrence of ferromagnetic resonance peak is usual behavior at higher
frequencies [36].On the other hand the magnetic loss (μ") is generated due to the delay of
magnetic dipoles in responding to the applied ac-field frequency. μ" is decreasing with
increase of frequency. Low magnetic loss of 0.209 is obtained for NF at 5 MHz. Generally
permeability is a grain size dependent property. Bulk materials possess particle size of micron
order containing smaller number of oxygen vacancies. While in case of nano materials
number of oxygen ion vacancy is much greater resulting in high pinning effect [37]. This
pinning effect reduces the domain wall motion leading to the decrease of permeability when
compared with their bulk counterpart. Relative loss factor (rlf, tan δm/μ') is the ratio of
magnetic loss tangent (tan δm) and permeability (Fig.12). This must be as small as possible
for device applications. In this study rlf is decreasing with increase of frequency and the
lowest value achieved is of order 4.49x10-4 at 5 MHz. Permeability related parameters’ data
are listed in Table.2.
Magnetic properties of ferrites such as magnetization (Ms), remanance (Mr),
coercivity (Hc), anisotropic energy (K1 ~ HcMs/0.96), squareness (Mr/Ms), M-H loop area (A)
and magnetic moment (nB) are affected by cationic distribution in the sites, surface area and
density. The M-H loop (hysteresis loop) is traced for NF nano-particles at room temperature
(300K) and is shown in Fig. 13. The corresponding magnetic parameters are reported in
Table. 3. As far as the cationic distribution of nano NF is concerned Ni+2 ions occupy B-site
as well as A-site [5] and hence few Fe+3 ions are migrated from B-site to A-site. If MA and
MB are the magnetic moments of tetrahedral and octahedral sites respectively, the net
magnetic moment (M = MB-MA) is equal to the experimental value of 2.417. Therefore the
possible cationic distribution can be written as [Ni0.205 Fe0.888]A [Ni0.795]B[Fe1.112]BO4. In this
study nano-NF exhibited more Ms of 57.6 emu/g and nB of (2.417μB) than the reported value
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using solvothermal technique [10] due to high specific surface area (low crystallite size) [1].
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The critical diameter (Dc) is calculated from the following relation [38] and found to be 15.4
nm.
Dc =
1.4εp
M2s
__________ (16)
where εp = (2KbTcK1/a)1/2 is domain wall energy density, Ms (Gauss), Kb (1.38 x 10-16 erg/K),
Tc(K) is the Curie temperature, K1(erg/cm3)and a is lattice parameter (cm) [39]. The obtained
Dc (15.4 nm) is of order of crystallite diameter (D) of 8.9 nm. It is well known fact that if Dc>
D the generated Hc is the contribution of domain wall displacement. Likewise, Dc ~ D, the
coercivity is the resultant of domain wall rotation [38]. Therefore, in this investigation the Hc,
65.1 G is attributed to domain-wall rotation.
Fig.14 (a) depicts the variation of magnetization as a function of temperature (M-T
curve) of nano NF. Zero-field cooled (ZFC) magnetization measurements are carried out by
cooling the NF in the zero magnetic fields and then the temperature is increased from 0-300
K under the applied field of 100 G. In the same way the field-cooled (FC) magnetizations are
recorded by cooling NF from 300-0 K in 100 G static field. The ZFC curve shows the
maximum magnetization (~ 40 emu/g) at around 260 K. This suggests the blocking of nano
particles at 260 K (TB) [40]. For the temperature greater than blocking temperature (T>TB
i.e.>260 K) the single domain particles magnetic moment is progressively unblocks and the
magnetization in the presence of magnetic field attains its thermal equilibrium value like an
atomic paramagnet. However, since the magnetic moment of a single domain particle is
larger than that of an atom, the magnetic state for T>TB is called super paramagnetic which
exhibits almost zero values of coercivity and remanance of material [41]. In this study, it
happened at T>260 K. The super paramagnetic nature of nano NF particles is very much clear
from the M-H loop behaviour recorded at 270 K wherein the coercivity and remanance are
12
almost equal to zero (Fig.14 (b)). At room temperature also the narrow M-H loop with almost
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zero Mr and very small Hc values confirms the existence of super paramagnetic nature.
4. Conclusions
Nickel ferrite nano-particles are prepared by hydrothermal technique. The obtained
crystallite size is 8.9nm with good crystallinity. The selected area electron diffraction
(SAED) confirms the formation of nano NiFe2O4 phases. Cole-Cole plots are drawn for
complex impedance and dc-conductivity is found to be 1.29 x 10-6 S/cm. The as-prepared
samples show high saturation magnetization of 57.6 emu/g and coercivity of 65.1 G. The MT curve shows maximum magnetization ~ 40 emu/g at blocking temperature TB ~ 260 K and
for T>TB the NF shows super paramagnetic nature. The low dielectric constant of 6.79 and
low loss tangent of 0.201 are obtained at 5 MHz. The achieved low magnetic loss and low
relative loss factor 4.49 x 10-4 at 5 MHz are suitable for high frequency magnetic
applications.
Acknowledgement
This
work
is
financially
supported
by
DRDO
Project,
No.
ERIP/EP/1103015/M/01/1484/ dtd.20.06.13, New Delhi. Also acknowledge to SIF at SAS,
VIT University, Vellore and Dr. S. Manjunatha Rao from Central University Hyderabad for
providing XRD, FTIR and VSM (M-T curve) facilities respectively.
References
1) M.H. Mahmoud, A.M.Elshahawy, SalahA.Makhlouf, H.H.Hamdeh, Synthesis of
highly ordered 30nm NiFe2O4 particles by the microwave-combustion method,
Journal of Magnetism and Magnetic Materials 369 (2014) 55–61
13
2) M. YasirRafique, MujtabaEllahi, M.ZubairIqbal, Qurat-ul-ainJaved, LiqingPan, Gram
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
scale synthesis of single crystalline nano-octahedron of NiFe2O4: Magnetic and
optical properties, Materials Letters 162 (2016) 269–272
3) M.A. Gabal, S. Kosa, T.S. Al Mutairi, Structural and magnetic properties of Ni1xZnxFe2O4
nano-crystalline ferrites prepared via novel chitosan method, Journal of
Molecular Structure 1063 (2014) 269–273
4) E. RanjithKumar, R.Jayaprakash, SanjayKumar, The role of annealing temperature
and bio template (egg white) on the structural, morphological and magnetic properties
of manganese substituted MFe2O4 (M = Zn, Cu, Ni, Co) nanoparticles, Journal of
Magnetism and Magnetic Materials 351(2014)70–75
5) M. Atif, M. Nadeem, M. Siddique, Cation distribution and enhanced surface effects
on the temperature-dependent magnetization of as-prepared NiFe2O4 nanoparticles,
Applied Physics A 120 (2015) 571–578
6) ChuleepornLuadthong,
KajornsakFaungnawakij,
VorranutchItthibenchapong,
PrasertPavasant,
NawinViriya-empikul,
WiwutTanthapanichakoon,
Synthesis,
structural characterization, and magnetic property of nanostructured ferrite spinel
oxides (AFe2O4, A = Co, Ni and Zn), Materials Chemistry and Physics 143 (2013)
203-208
7) M. Yehia, Sh.Labib, S.M.Ismail, Structural and magnetic properties of nano-NiFe2O4
prepared using green nanotechnology, Physica B 446(2014) 49–54
8) M. Khairy, Synthesis, characterization, magnetic and electrical properties of
polyaniline/NiFe2O4nanocomposite, Synthetic Metals 189 (2014) 34–41
9) T.F. Marinca, I. Chicinas, O. Isnard, V. Pop, F. Popa, Synthesis, structural and
magnetic characterization of nanocrystalline nickel ferrite-NiFe2O4 obtained by
reactive milling, Journal of Alloys and Compounds 509 (2011) 7931– 7936
14
10) HangsongZheng, Yonghong Ni, Nannan Xiang, Xiang Ma, Fengying Wan,
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
Solvothermal synthesis of octahedral NiFe2O4nanocrystals and catalytic properties for
the reduction of some aromatic Nitrocompounds, Materials Chemistry and Physics
158 (2015) 82-88
11) M.A.Gabal, RedaM.El-Shishtawy, Y.M.AlAngari,Structural and magnetic properties
of nano-crystalline Ni–Zn ferrites synthesized using egg-white precursor, Journal of
Magnetism and Magnetic Materials 324 (2012) 2258-2264.
12) M.A. Gabal, Y.M. Al Angari, Effect of chromium ion substitution on the
electromagnetic properties of nickel ferrite, Materials Chemistry and Physics 118
(2009) 153–160
13) H. Moradmard, S. F. Shayeshtech, P. Tohidi, Z. Abbas, M. Khalegi, Structural,
magnetic and dielectric properties magnesium doped nickel ferrites nano particles,
Journal of Alloys and Compounds 650 (2015) 116-122.
14) H.M. Zaki, S.H. Al-Heniti, T.A. Elmosalami, Structural, magnetic and dielectric
studies of copper substituted nano-crystalline spinel magnesium zinc ferrite, Journal
of Alloys and Compounds 633 (2015) 104–114
15) Solvothermal synthesis and magnetic properties of size-controlled nickelferrite
nanoparticles, JingyingWang, FenglianRen, Ran Yi, Aiguo Yan, GuanzhouQiu,
Xiaohe Liu, Journal of Alloys and Compounds 479 (2009) 791–796
16) M.H. Mahmoud, A.M.Elshahawy, SalahA.Makhlouf, H.H.Hamdeh, Synthesis of
highly ordered 30nm NiFe2O4 particles by the microwave-combustion method,
Journal of Magnetism and Magnetic Materials 369 (2014)55–61
17) Roberto Koferstein, Till Walther, Dietrich Hesse, Stefan G Ebbinghaus, Preparation
and characterization of nanosized magnesium ferrite powders by a starch-gel process
and corresponding ceramics, Journal of Material Science (2013) 48: 6509-651
15
18) Wen
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
Fan
Chen,
Hsin
Chen,
PramodKoshy,
and
Charles
Christopher
Sorrell,Photocatalytic Performance of Vanadium-Doped and Cobalt-Doped TiO2 thin
Films, Journal of The Australian Ceramic Society 51(2015) 1 – 8.
19) Gagan Dixit, J.P. Singh, R.C. Srivastava, H.M. Agrawal, R.J. Chaudhary, Structural,
optical and optical studies of nickel ferrite thin films, Advanced Materials Letters 3
(2012) 21-28.
20) H. Donnerberg, A. Birkholz, Ab initio study of oxygen vacancies in BaTiO3, Journal
of Condensed Matter Physics 12 (2000) 8239–8247.
21) H. Moradmard, S. F. Shayeshtech, P. Tohidi, Z. Abbas, M. Khalegi, Structural,
magnetic and dielectric properties magnesium doped nickel ferrites nano particles,
Journal of Alloys and Compounds 650 (2015) 116-122.
22) A.M. Dumitrescu, G. Lisa, A.R. Iordan, F. Tudorache, I. Petrila, A.I. Borhan,M.N.
Palamaru, C. Mihailescu, L. Leontie, C. Munteanu, Ni ferrite highly organized as
humidity sensors, Materials Chemistry and Physics 156 (2015) 170-179
23) A. A. Sattara, H. M. EL-Sayeda, Ibrahim ALsuqia, Structural and magnetic properties
of CoFe2O4/ NiFe2O4 core/shell nanocomposite prepared by hydrothermal method,
Journal of Magnetism and Magnetic materials 395 (2015) 89-96.
24) Jitendra Pal Singh, Gagan Dixit, R.C. Srivastava, H.M. Agrawal, Ravi Kumar, Raman
and Fourier-transform infrared spectroscopic study of nanosized zinc ferrite irradiated
with 200 MeV Ag15+ beam, Journal of Alloys and Compounds 551 (2013) 370–375.
25) M.A.Gabal, RedaM.El-Shishtawy, Y.M.AlAngari,Structural and magnetic properties
of nano-crystalline Ni–Zn ferrites synthesized using egg-white precursor, Journal of
Magnetism and Magnetic Materials 324 (2012) 2258-2264.
26) K. Wagner, Annals of Physics 40 (1913) 817
16
27) L. J. Berchmens, R. K. Selvan, P. N. S. K4umar, C. O. Augustin, Structural and
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
electrical properties of Ni1-xMgxFe2O4 synthesized by citrate gel process , Journal of
Magnetism and Magnetic materials 279 (2004) 103-110.
28) M. A. Gabal, Y. M. AlAngari, H. M. Zaki, Structural, magnetic and electrical
characterization of Mg–Ni nano-crystalline ferrites prepared through egg-white
precursor. Journal of Magnetism and Magnetic Materials 363(2014)6–15.
29) Dinesh Varshney, KavitaVerma, Substitutional effect on structural and dielectric
properties of Ni1-xAxFe2O4(A = Mg, Zn) mixed spinel ferrites, Materials Chemistry
and Physics 140 (2013) 412-418
30) Z. V. Mocanu, M. Airimioaei, C. E. Ciomaga, L. Curecheriu, F. Tudorache, S. Tascu,
A. R. Iordan, NN. M. Palamaru, L. Mitoseriu, Investigation of the functional
properties of MgxNi1-xFe2O4 ceramics, J Mater Sci, DIO: 10.1007/s10853-014-8033-6
31) A.S.Dzunuzovic, N.I.Ilic, M.M.VijatovicPetrovic, J.D.Bobic, B.Stojadinovic, Z.
Dohcevic-Mitrovic, B.D.Stojanovic, Structure and properties of Ni–Zn ferrite
obtained by auto-combustion method, Journal of Magnetism and Magnetic Materials
374(2015)245–251
32) Rajiv Ranjan, Nawnit Kumar, Banarji Behera, R. N. P.Choudhary, Investigations of
impedance and electric modulus properties of Pb1-xSmx(Zr0.45 Ti0.55)1-x/4O3 ceramics,
Advanced Maerials Letters 5 (2014) 138-142
33) BaskaranSenthilkumar,
IlanaPerelshtein,
RamakrishnanKalaiSelvan,
AharonGedanken,
Structural,
PalanisamyVinothbabu,
magnetic,
electrical
and
electrochemical properties of NiFe2O4 synthesized by the molten salt technique,
Materials Chemistry and Physics 130 (2011) 285– 292
34) J.S. Ghodake, T.J.Shinde, R.P.Patil, S.B.Patil, S.S.Suryavanshi, Initial permeabilityof
Zn–Ni–Co ferrite, Journal of Magnetism and Magnetic Materials 378(2015)436–439.
17
35) P. K. Roy, J. Bera, Study on electromagnetic properties of MgCuZn ferrite/ BaTiO3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
composites, Materials Chemistry and Physics 132 (2012) 354-357.
36) Charalampos A. Stergiou, George Litsardakis, Y-type hexagonal ferrites for
microwave absorber and antenna applications, Journal of Magnetism and Magnetic
Materials 405 (2016) 54–61
37) S.Song, Q.Song, J.Li, M.V.Ramana, Z.Zhang, Characterization of sub-micrometersized NiZn ferrite prepared by spark plasma sintering Ceramics International 40
(2014) 6473-6479.
38) CosticaCaizer, Nanoparticle Size Effect on Some Magnetic Properties, Handbook of
Nanoparticles,
DOI
10.1007/978-3-319-13188-7-24-1,
Springer
International
Publishing Switzerland 2015
39) C. Caizer, M. Stefanescu, Nanocrystallite effect on σs and Hc in nanoparticles
assemblies, Physica B 327 (2003) 129-134.
40) S. N. Dolia, Subhash Chander, M. P. Sharma, Sudhish Kumar, Super paramagnetic
behaviour of nanoparticles of Ni-Cu ferrite, Indian Journal of Pure and Applied
Physics 44 (2006) 169-172
41) M. Atif, M. Nadeem, M. Siddique, Cation distribution and enhanced surface effects
on the temperature-dependent magnetization of as-prepared NiFe2O4 nanoparticles,
Applied Physics A 120 (2015) 571–578
18
Table
Table.1. Data on structural parameters of nano NiFe2O4
Table.2. Data on electrical and permeability studies of nano NiFe2O4
Table.3. Data on M-H loop parameters of nano NiFe2O4
parameters
D (nm)
a (Å)
ρd x1014 (m-2)
FWHM (βavg)
dx (g/cc)
V
D (nm) from W-H plot
Scherrer Strain (ε*)
Strain (ε) from W-H plot
S x 103(m2/g) from TEM
Optical band gap Eg (eV)
values
20
8.327
126.2
0.023
5.392
577.4
3.2
0.0156
0.0075
55.67
1.57
literature
46.2
8.332
1.55
Reference
2
2
2
Table.1. Data on structural and optical parameters of nano NiFe2O4
Parameter
ε' (5 MHz)
ε"(5 MHz)
tan δe (5MHz)
σac (S/cm)
σdc (S/cm)
μi (5 MHz)
μ"(5 MHz)
tan δM (5MHz)
tan δm/μi (5MHz)
Q x f (5 MHz)
value
6.79
1.37
0.201
3.82x10-6
1.29x10-6
21.62
0.209
0.0097
4.49x10-4
103
Table.2. Data on electrical and permeability studies of nano NiFe2O4
Parameter
Ms (emu/g)
A (cm2)
Hc (G)
Mr (emu/g)
Mr/Ms
K1 (erg/cm2)
nB (μB)
εp (erg/cm2)
Dc (nm)
value
57.6
1551.1
65.1
0.714
0.1024
21061.2
2.417
0.244
15.4
literature
54.8
59.4
9.8
-
Reference
10
10
2
-
Table.3. Data on M-H loop parameters of nano NiFe2O4
1
Figure
Figure Captions:
Fig.1. Schematic diagram of synthesis part of nano NiFe2O4
Fig.2 (a) XRD pattern of NiFe2O4 nano-particles
(b) W-H plot of NiFe2O4 nano-particles
Fig.3. TEM image and SAED pattern of NiFe2O4 nano-particles
Fig.4. FESEM image and EDS spectra of NiFe2O4 nano-particles
Fig.5 Plot of (αhν)2 as a function of hν (photon energy)
Fig.6. FT-IR spectra of NiFe2O4 nano particles
Fig.7. Variation of (a) real (ε') & imaginary (ε") part of complex permittivity and (b) loss tangent
(tanδ) & quality factor (Qxf) with frequency
Fig8.lnσ Vs frequency plot
Fig.9. Z' Vs. Z" plot (Nyquist plot) of NiFe2O4 at room temperature (RT)
Fig.10. M' Vs. M" plot at RT
Fig.11 Frequency dependence of real (μ') and imaginary (μ") part of permeability at RT
Fig.12 Frequency dependence of relative loss factor (tanδ/μ')
Fig.13 The M-H loop behavior of NiFe2O4 nano-particles
Fig.14 The (a) M-T curve and (b) M-H loop (at 270 K) behavior of NiFe2O4 nano-particles
1
Fig.1. Schematic diagram of synthesis part of nano NiFe2O4
2
Fig.2 (a) XRD pattern of NiFe2O4 nano-particles
0.24
y x
NF
cos
0.16
0.08
0.00
-0.08
0.5
1.0
1.5
2.0
2.5
4 sin
Fig.2 (b) W-H plot of NiFe2O4 nano-particles
3
(a)
(b)
(311)
(400)
(511)
(440)
Fig.3. TEM image and SAED pattern of NiFe2O4 nano-particles
Element
OK
Fe L
Ni L
Total
Wt%
35.45
38.97
25.58
100.0
At%
66.15
20.84
13.01
100.0
Fig.4. FESEM image and EDS spectra of NiFe2O4 nano-particles
4
2.4
nano NF
bulk NF
2.1

2
h eV/cm)
1.8
1.5
1.2
0.9
1.45 eV
1.57 eV
0.6
1.0
1.5
2.0
2.5
3.0
h (eV)
Fig.5 Plot of (αhν)2 as a function of hν (photon energy)
96
nano NF
3432.3
88
76
449.5
80
1364.3
2926.4
1628.2
84
2849.1
transmittance (% T)
92
583.4
4000
3500
3000
2500
2000
1500
1000
500
-1
Wave number (cm )
Fig.6. FT-IR spectra of NiFe2O4 nano particles
5
'
"
160
(a)
140
1000
800
120
600
80
"
'
100
400
60
200
40
20
0
0
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
log 
tan 
Qxf
5
(b)
5
4
3
3
2
2
1
1
tan 
Qxf
4
0
4.5
0
5.0
5.5
6.0
6.5
7.0
7.5
log 
Fig.7. Variation of (a) real (ε') & imaginary (ε") part of complex permittivity and (b) loss tangent
(tanδ) & quality factor (Qxf) with frequency
6
-5.0
ac-conductivity
-5.2
log ac
-5.4

dc
= 5.9 x 10
-6
S/cm
-5.6
-5.8
-6.0
-6.2
2
3
4
5
6
7
8
log 
Fig8.lnσ Vs frequency plot
5
4x10
5
Z" ()
3x10
5
2x10
5
1x10
0
5
1x10
5
5
2x10
3x10
5
4x10
Z' ()
Fig.9 Z' Vs. Z" plot (Nyquist plot) of NiFe2O4 at room temperature (RT)
7
0.14
T = 313K
0.12
M"
0.10
0.08
0.06
0.04
0.02
0.00
0.00
0.03
0.06
0.09
0.12
0.15
M'
Fig.10 M' Vs. M" plot at RT
22.8
15
'
"
12
22.4
9
22.0
"
'
fr (0.4 MHz)
6
21.6
3
0
21.2
5.5
6.0
6.5
7.0
7.5
log 
Fig.11 Frequency dependence of real (μ') and imaginary (μ") part of permeability at RT
8
0.12
0.10
rlf (tan/ i)
0.08
0.06
0.04
0.02
0.00
4.5
5.0
5.5
6.0
6.5
7.0
7.5
log 
Fig.12 Frequency dependence of relative loss factor (tanδ/μ')
60
Magnetization (emu/g)
40
NiFe2O4
20
0
-20
-40
-60
-6000
-4000
-2000
0
2000
4000
6000
Magnetic field H (G)
Fig.13 shows the M-H loop behavior of NiFe2O4 nano-particles
9
b
a
Fig.14 The (a) M-T curve and (b) M-H loop (at 270 K) behavior of NiFe2O4 nano-particles
10