The lattice parameter and cell volume are in resemblance trend with the variation of the dopant concentration. The similar trend is observed for the crystallite and particle size. The porosity and sintered density, however, vary in an opposite way with a variation of the dopant concentration. The same variation is found for the drift mobility and DC resistivity.
Trang 1Original Article
Structural, electrical and magnetic properties of Mg-Zr co-substituted
Ni 0.5 Zn 0.5 Fe 2 O 4
K Jalaiaha,b,*, K Chandra Moulic, K Vijaya Babud, R.V Krishnaiahe
a Chebrolu Engineering College, Chebrolu, Guntur, 522212, India
b Department of Physics, Andhra University, Visakhapatnam 530003, India
c Department of Engineering, Physics, Andhra University, Visakhapatnam 530003, India
d Advanced Analytical Laboratory, Andhra University, 530003, India
e Institute of Aeronautical Engineering and Technology, Hyderabad, 500043, India
a r t i c l e i n f o
Article history:
Received 2 October 2018
Received in revised form
15 December 2018
Accepted 16 December 2018
Available online 23 December 2018
Keywords:
Ferrites
XRD
TEM
SEM
Permeability
Saturation magnetization
Anisotropy constant
a b s t r a c t
Zr and Mg co-substituted Ni0.5Zn0.5Fe2O4ferrites have been synthesized by the sol-gel auto-combustion method The X-ray diffraction patterns evidenced the single phase cubic spinel structure The lattice parameter and cell volume are in resemblance trend with the variation of the dopant concentration The similar trend is observed for the crystallite and particle size The porosity and sintered density, however, vary in an opposite way with a variation of the dopant concentration The same variation is found for the drift mobility and DC resistivity The Arrhenius graphs of DC resistivity exhibit the semiconductor nature, for which the activation energy decreased with increasing the dopant concentration Moreover, as the dopant contents increased, the saturation magnetization, net magnetic moment and permeability are reduced, while the coercivity is reinforced Thesefindings can be correlated with the variation of the porosity and grain size
© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
1 Introduction
In early days iron based magnetic alloys are used in various
applications However, their low resistivity made these materials
inefficient at high frequencies, which encouraged the eddy current
through them This wasted energy is created a serious problem that
generated the heat in the circuit Hence, iron based magnetic
ma-terials are not favorable in high frequency applications Ferrite
materials, in opposite, possess high resistivity and dielectric
per-formances and do not conduct the electric current readily The
advantage of ferrites over magnetic alloys is that they formed a
different combination of ferrites with transition metals because the
transition metals exhibit magnetic as well as semiconductor
properties The porosity is an insignificant factor for ferrites so that
the ferrites have been investigated for several years based on this
issue In order to get the high resistivity of ferrites researchers
choose different combination here we also choose a new combi-nation with transition metals to get the high resistivity of ferrite material[1,2] Spinal ferrites are a class of magnetic oxides with the general formula of AB2O4 They are categorized as soft and hard ferrites according to their magnetic performance Soft ferrites are easily demagnetized without significant energy need, i.e only a small energy amount is wasted in the form of eddy currents to demagnetize the soft magnetic materials In case of hard ferrites, a significantly higher energy is needed to demagnetize This means that soft magnetic materials possess higher electrical resistivity, thus, they are used in inductors and transformers The magnetic oxides are made from the blend of iron, nickel, zinc, manganese oxides By using these oxides, different combinations of soft ferrites like Manganese-Zinc and Nickel-Zinc have been prepared For inductor cores, the magnetic permeability is the chief parameter
[3,4] In order to improve the core performance at high frequency the grain size, which can be controled by the ferrite preparation technique, plays an important role The solid state ceramic tech-nique is a general ferrite fabricated techtech-nique, in which the con-stituent oxides react at higher temperatures In this case, an unusual grain growth usually occurs due to the non stoichiometry
* Corresponding author Chebrolu Engineering College, Chebrolu, Guntur,
522212, India.
E-mail address: kjalu4u@gmail.com (K Jalaiah).
Peer review under responsibility of Vietnam National University, Hanoi.
Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d
https://doi.org/10.1016/j.jsamd.2018.12.004
2468-2179/© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license
Trang 2and inhomogeneity of ferrite materials[5] To control this unusual
grain growth, we adopted the solution method known as the
sol-gel autocombustion method in which the constituent oxides react
at lower temperatures So, the precursor material becomes
stoi-chiometry and homogeneity with controlled grain size In the
present study, the correlation between structural, electrical and
magnetic properties of Mg-Zr co-substituted Ni0.5Zn0.5Fe2O4 are
discussed in connection with the dopant concentration
2 Experimental
The Zr and Mg co-substituted Ni0.5Zn0.5ZrxMgxFe2-2xO4have
been prepared by sol-gel auto combustion method, x values vary
from the 0.08 to 0.4 in steps of 0.08 with% The starting
mate-rials of all metal nitrates with AR grade Nickel nitrate
(Ni(NO3)2.6H2O), zinc nitrate (Zn (NO3)2.6H2O), Magnesium
ni-trate (Mg(NO3)2.6H2O), Zirconyle nitrate (ZrO (NO3)2), ferric
citrate (Fe C6H8O7.H2O) and citric acid (C6H8O7.H2O) are used for
synthesis of Ni0.5Zn0.5ZrxMgxFe2-2xO4(x¼ 0.08, 0.16, 0.24, 0.32,
0.4) The stoichiometric weights of metal nitrates dissolved in
deionized water and the citric acid added to the solution as per
the oxygen ions present in chemical formula, later 50 ml
ethylene glycol added to the solution[6] The ammonia solution
added drop wise to adjust the PH value of 7 for thefinal
solu-tion Then the neutralizing solution heated to 600oCe700C for
turned into a viscous on the formation of gel, then the
tem-perature of a gel rise to 100C drying,finally a powder form of
simple experimental needs
3 Structural studies
Fig 1 shows the XRD patterns of Mg and Zr co-substituted
Ni0.5Zn0.5Fe2O4 Here the XRD patterns provide the evidence for
single phase cubic spinel and no extra peaks are observed
throughout while the doping concentration is increased The lattice
constant is calculated from XRD peaks, using the following
equation
a¼ dpffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2þ k2þ l2
where d is the space between the lattice planes The lattice constant
and cell volumes are shown inFig 2a with a variation of dopant
concentration The increase in the lattice constant has resulted in
mismatches between the substitute ions and host ions ionic radius The Fe3þ (0.67Å) ions radius is small when compared with Zr (0.80Å) and Mg (0.72 Å) ionic radii Hence the substitution of Zr and Mg in place of the Fe3þions unit cell will bulge promptly and as
a result the lattice constant increases with increasing dopant con-centration[8] The X-ray density is estimated from the following equation
Dx¼ 8M
Naa3
where M is the molar mass, Na is the Avogadro number and“a”
is the lattice constant The X-ray density increases with increasing dopant concentration from x¼ 0.08 to x ¼ 0.32, later it is slightly decreased to x¼ 0.4 However, overall X-ray density increases with increasing dopant concentration The increase in X-ray density may
be due to the lattice constant which is dominated by the molar mass as shown in the above equation because the increase in the lattice constant decreases the X-ray density The ratio between the sintered density and X-ray density gives the porosity of prepared samples The porosity of prepared samples is estimated from the following equation
p¼ 1 ds
dx
where“ds” and “dx” are sintered and x-ray densities respectively The porosity and sintered density are shown in Fig 2b with a variation of dopant concentration FromFig 2b it is clear that both the parameters exhibit opposite trend with a variation of dopant concentration The sintered density is decreased as a result of lag-ging the sintering rate of material The sintering rate of material is lagging due to the volatilization of zinc at higher temperature Since the melting point of zinc is less than those of other constituent ions, the material becomes non stoichiometry[9] To minimize the non stoichiometry property of the material, the excess of ferric oxide is changed as ferrous oxide, i.e., Fe3þions are changed as Fe2þions in the sintering process The presence of Fe2þions in the material lags the sintering rate of material, hence sintered density is decreased
[10] The decrease in the sintered density results in the develop-ment of pores in the material
4 Surface morphology The crystallite size is estimated from the following equation
D¼0:94*l
bcosq
wherelis the wavelength of Cu radiation andbis the full width half maximum of (3 1 1) peak The FWMH is decreased with increasing substituting ionic radii so that the decrease in the FWHM increases the crystallite size since crystallite size and FWHM are inversely related in the above equation.Fig 2c shows the crystallite size and particle size with a variation of dopant concentration The TEM pictures are shown inFig 3 The particle size is measured from TEM pictures by using image-j software The particle size increased with increasing dopant concentration
as a result of the agglomeration nature of crystallites[11] From
Fig 2c we conclude that both the crystallite size and the particle size are in comparable nano size The SEM micrographs of pre-pared samples are shown inFig 4 The grain size is measured from SEM micrographs by using the image-j software The grain size decreased with increasing dopant concentration The decrease in grain size is due to the development of pores in the material during the sintering of material
Fig 1 X-ray diffraction patterns of Ni 0.5 Zn 0.5 Zr x Mg x Fe 2-2x O 4 samples with x ¼ 0.08,
K Jalaiah et al / Journal of Science: Advanced Materials and Devices 4 (2019) 310e318 311
Trang 35 DC resistivity
The ferrites exhibit the semiconducting nature since ferrites are
composed of transition elements and all transition elements show
the semiconducting nature.Fig 5shows composition variation of
DC resistivity and drift mobility of prepared ferrite samples The DC
resistivity of ferrite samples decreased with increasing doping
concentration The decrease in DC resistivity because of the
increased electronic conduction between the paramagnetic region
(Fe2þions) to ferromagnetic (Fe3þions) region [12] That is the
electronic exchange has occurred in ferrites from Fe2þ(n-type) to
Fe3þ(p-type) InFig 5the drift mobility varies opposite to DC
re-sistivity with increasing doping concentration, since the decrease
in DC resistivity increases the mobility of electrons The Arrhenius
plots drawn between DC resistivity and inverse temperature in the
range of 300 K and 620 K show that all plots are less curved So
these plots reveal the semiconducting nature of prepared samples
The Arrhenius plots for the present study are shown inFig 6 The
semi conductivity of ferrite samples is described by the following
equation
s¼soexp
DE
kBT
where so is the constant,DE is the activation energy, KB is the
Boltzmann constant and T is the absolute temperature The graph
betweensand 1/T gives more or less a curved line TheDE equals 0.1eV for stoichiometry composition andDE reaches 0.5eV for low conductivity ferrites[13] For the present study the Activation en-ergyDE decreased from 0.17eV to 0.11eV i.e the activation energy, decreased with increasing dopant concentration and it is shown in
Fig 7 The decrease in activation energy is due to increase of jumping frequency of electrons from the paramagnetic region (Fe2þ) to the ferromagnetic region (Fe3þ)[14]
6 Magnetic properties The magnetic properties of Mg and Zr substituted Ni0.5Zn0.5
-Fe2O4ferrites are calculated by using the M-H loops shown in
Fig 8 All the M-H loops are with less loss of magnetic energy and the M-H loop data is collected at room temperature The satura-tion magnetizasatura-tion and the corresponding net magnetic moment are estimated from M-H loops Both the saturation magnetization and the corresponding net magnetic moment are in decreasing trend with increasing dopant concentration as shown inFig 9a The decrease in saturation magnetization is due to the decrease of
Fe3þions in general formula with the substitution of Mg and Zr ions in place of Fe3þions The presence of Fe3þions in the material needs a much moreflux to orient in the applied field direction Since Fe3þions behave like ferromagnetic ions the Fe3þions need
Fig 2 (a) variation of lattice parameter and cell volume with dopant concentration (b) variations of sintered density and porosity with dopant concentration (c) the variation of particle size and Crystallite size with dopant concentration.
Trang 4decreased Fe3þions in material need lesserflux density to orient in
decreased with increasing dopant concentration Father the net
magnetic moment of the material is calculated using the following
equation
M¼ MA MB
here MAand MB are the magnetic moments of A-site and B-site respectively From the above equation the resultant magnetic
Fig 3 Transmission electron micrographs of Ni 0.5 Zn 0.5 Zr x Mg x Fe 2-2x O 4 along with selected area Electron diffraction patterned of samples.
K Jalaiah et al / Journal of Science: Advanced Materials and Devices 4 (2019) 310e318 313
Trang 5Fig 4 Schematic SEM photo graphs of Zr and Mg Co substituted Ni 0.5 Zn 0.5 Zr x Mg x Fe 2-2x O 4
Fig 5 Compositional variation of D.C resistivity and Drift mobility Fig 6 Variation of logrwith inverse temperature.
Trang 6moment of material is the difference between the B-site magnetic moment and A-site magnetic moment The increase in A-site magnetic moment decreases the resultant material magnetic moment The substituted Mg and Zr in place of Fe3þions, occupy the A-site and B-sites for their comfortablefit in lattice sites While Zr enters A-site, it replaces the Fe3þions from A-site to B-site To give place for Fe3þions in B-site the Ni2þions are converted as Ni3þions
by releasing an electron And by taking the electron from Ni ion,
Fe3þion is changed as Fe2þion [16,17] Moreover the A-site spin magnetic moment is always opposite to the B-site spins magnetic moment, hence the net magnetic moment is decreased with increasing dopant concentration The Fe3þions from A-site will be arranged anti parallel in B-site upto certain concentration, later
Fe3þions from A-site will be arranged on B-site with canting posi-tion This gives an angle between the Aesite Fe3 þions and
B-site-Fe3þions called Y-K angle[18] The Y-K angle is calculated by using the following equation
nB¼ ð6 þ xÞcosaYK 5ð1 xÞ Fig 7 Variation of activation energy with dopant concentration.
Fig 8 Magnetization versus magnetic field (M-H) curves of Zr and Mg substituted Ni Zn Zr Mg Fe O at room temperature.
K Jalaiah et al / Journal of Science: Advanced Materials and Devices 4 (2019) 310e318 315
Trang 7The variation of Y-K angles with dopant concentration is
shown inFig 9b FromFig 9b it is clear that Y-K angles increased
with increasing dopant concentration The increase in the Y-K
angles suggests the increase of AeB interaction[19] The coercive
field is a field where the magnetization becomes zero in reverse
order The composition variation of Coercivefield and porosity is
shown inFig 9c FromFig 9c it is concluded that the increase in
the porosity increases the coercivefield According to J Smith and
H.P.J Wijn the increase in the porosity of the material will affect
applied magneticfield magnetic dipoles will not come to initial
magnetic dipoles suffer by residualflux) This lagging of field is affected by the porosity of samples[21] Hence an increase in porosity increases the coercivefiled
7 Magnetic permeability Permeability is the property of a magnetic material which measures its ability to support the formation of magneticfields within itself The extent of the magnetization of a material denotes the response to an applied magneticfield The permeability of the material is estimated from the following equation
m¼ L
L0 Fig 9 Variation of net magnetic moment and saturation magnetization (a), Y-K angles (b), coercive field and porosity (c), and permeability and grain size (d) with dopant concentration.
Trang 8where L is the measured inductance of the torroids and Lo is
calculated as follows
Lo¼ 4:606N2log
OD ID
t 109Henry Fig 9d shows the variation of the initial permeability and grain
size with the dopant concentration FromFig 9d it is clear that the
permeability decreases with increasing dopant concentration, since
the permeability and the grain size are related as shown in the
following equation
K¼ cd2
here K is the permeability, c is the dimension less constant and d is
the grain size Hence permeability is directly proportional to the
square of the grain size The materials composed with grains
include the atomic dipoles or spin dipoles[22] The existed atomic
dipoles or spin dipoles in grains are oriented randomly By the
application of externalfields, the atomic dipoles or spin dipoles in
grains align with thefield direction This is related to the induced
in-crease up to a certain frequency In this case, a resonance peak will
appear where the frequency of the appliedfield equals the spin
dipoles or atomic dipoles It means that the maximum magnetic
flux is induced in the material at the resonance frequency Later
literature survey the resonance peak appearance connects to: (i)
inhomogeneous material, (ii) crystalline magnetic anisotropy, (iii)
the combination of the magnetic anisotropy and the
permeability in the present study is shown inFig 10 From the
Fig 10 it is clear that all samples exhibit the resonance peak around the 12 MHz to 13 MHz The resonance effects occur in all ferrous and paramagnets In particular, it is not peculiar to ferrites
in its simple form Generally, it has been considered that the resonance in ferrites accounts for a large part of the magnetic dispersion of ferrites The permeability arises from the rotation of magnetic dipoles rather than from a domain wall displacement process The domain wall displacement does not account for magnetic dispersion at higher frequency[23] More complex type resonances are considered in ferromagnetic and antiferromag-netic materials, the sample shape anisotropy is taken into account
in this case Sometimes there may be two or more resonance frequencies possible in an accessible range of frequency In this case, domain wall effects will be considered The moving wall sets
up a magnetic double layer in the wall, and as a result the addi-tional energy acquires its static value Another resonance fre-quency appears due to body-resonance which accounts for the high permeability and high permittivity[24] Both are comparable
at body resonance frequency and as a result, the permeability and permittivity of a material may give too small values The perme-ability and anisotropy constant are shown inFig 11with dopant concentration The permeability and anisotropy constant are related as shown in following expression
mi∞M2sD K
From the above relation, the initial permeability is directly proportional to the square of saturation magnetization, and inversely proportional to anisotropy constant The permeability strongly depends on the homogeneity of the material That means, permeability depends on the grain size, intra and intergranular porosity of material If they are not explained well, then the
Table: 1
The structural data of Zr and Mg substituted Ni 0.5 Zn 0.5 Zr x Mg x Fe 2-2x O 4
Dopant
concentration
Lattice parameter(Å)
Crystallite size (nm)
X-ray density g/cm 3
Porosity (%) Sintered
density g/cm 3
Grain size (mm)
Particle size (nm)
Table: 2
The DC resistivity data of Zr and Mg substituted Ni 0.5 Zn 0.5 Zr x Mg x Fe 2-2x O 4
Dopant concentration DC resistivity(r)
U-cm
Drift mobility(h) 10 36 Activation energy (DE) eV
Table: 3
The magnetic properties of Zr and Mg substituted Ni 0.5 Zn 0.5 Zr x Mg x Fe 2-2x O 4
Dopant concentration Net Magnetic
momenthB
Saturation magnetization emu/gm
Coercive field (Hc)Oe
Anisotropy constant(K)
Y-K angles (⁰) Permeability
K Jalaiah et al / Journal of Science: Advanced Materials and Devices 4 (2019) 310e318 317
Trang 9permeability mechanism must be governed by some other
There are three types of magnetic anisotropy (1) crystal structure,
(2) grain shape and (3) applied stress or residual stresses The
crystal structure anisotropy is independent of grain size and shape
and it can be easily observed by measuring the magnetic curves in
different crystal directions The interaction of the spin magnetic
moment with the crystal lattice gives easy and hard directions
The magnetized body produces the poles or charge distribution at
the surfaces As a result, the magnetized body itself acts as another
demagnetizingfield acts opposite to the magnetizing field, and it
permeability decreases In short, decreasing the shape of
magnetizing body effects the permeability In case of round
sha-ped magnetized body, the anisotropy constant will be higher and
for cube shape, the anisotropy constant will be low The
perme-ability will be low for round shaped magnetize body, and for cube
shape it will be higher FromFig 4, magnetized bodies other than
the cube shape should be grown, so that the anisotropy constant
will be high As a result, the permeability decreases with
increasing dopant concentration The third one arises due to the
spin-orbit coupling that produces strain along the
crystallo-graphic axis So, the magnetized body will change directions when
magnetized[13]
8 Conclusion
The Zr and Mg co-substituted Ni0.5Zn0.5Fe2O4 ferrites have
been prepared by sol-gel auto combustion method The
investi-gated samples revealed the semiconducting nature, in which the
activation energydecreased with increasing dopant
concentra-tion The XRD patterns confirm the single phase cubic spinel and
no secondary phase was identified by this analysis The lattice
constant, cell volume as well as the porosity of samples increased
with increasing the dopant concentration The density of material,
as a consequence, decreased by pores developed in the material
The crystallite and particle sizes are comparable in the nano scale
As the dopant content varies, the DC resistivity and drift mobility
varied in the opposite way The saturation magnetization, net
magnetic moments and permeability are reduced with increasing
constant are enhanced The Y-K angles increase with increasing
dopant concentration Electrical and magnetic properties have
been discussed in good correlation with the structural behaviour
(seeTables 1e3)
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