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CHAPTER-IV
EXPERIMENTAL DETAILS
4.1 Introduction
Different
experimental
techniques
employed
in
the
present
investigations for the studies of the ferrites have been described in this
chapter. Description of preparation of materials along with their
characterization is presented. The experimental methods adopted and the
description of the instruments used to study the x-ray diffraction pattern,
morphology and microstructure, magnetic and electrical properties are
presented.
4.2 Sample preparation
A series of having general formula Ni0.7-xCuxZn0.3Fe2O4 x=0.00,
x=0.05, x=0.10, x=o.15, x=0.20, x=0.25, x=0.30, x=0.35, x=0.40, x=0.45,
x=0.50 have been synthesized by conventional ceramic method.
Highly pure analytical reagent grade NiO, CuO, ZnO and Fe2O3
chemicals were used. The oxides were taken in correct proportions, crushed
and mixed thoroughly for 5 hours in methanol using agate mortar and pestle.
The mixture was calcinated for 4 hours at 9000C in muffle furnace and then
it was allowed to cool in the furnace. Binder was added to the compound
formed after crushing it. The material was granulated through sieves and the
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granules were palletized. The pellets and toroids were finally sintered at
11000C in Nabertherm Furnace with Eurotherm controller. Then the furnace
was allowed to normal cooling in air atmosphere. The steps followed in the
preparation of the samples are shown in the typical flow chart in figure 4.1.
Fig. 4.1 shows the flow chart of the sample preparation.
4.3 Characterization of Material
Before studying different properties of ferrites, the processed ferrite
should be characterized to check whether ferrite was formed correctly or not.
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The properties of the basic ferrite Ni0.7Zn0.3Fe2O3 has been put to the
following measurements for characterization. They are
a)
Lattice constant obtained by the x-ray diffraction studies.
b)
Curie temperature of the material.
compared with reported values and are given in table.1.
Table.1: Shows the observed and reported values of Ni0.7Zn0.3Fe2O4
Composition
Ni0.7Zn0.3Fe2O4
Ni0.7Zn0.3Fe2O4
Parameter
Observed
value
Reported
value
8.3785
8.3970
502
558
Lattice
constant
(Ao)
Curie Temperature (Tc)
4.4 Experimental Measuring Techniques
Description and details about all the experimental techniques utilized
in the present investigations have been provided in this section.
4.4.1 X-ray diffraction and lattice constant
X-ray diffraction (XRD) patterns were obtained for structural analysis
using Philips diffractometer (model PW-3710) at Advanced Analytical
Labaratories Andhra University, Visakhapatnam. The x-rays for these
experimental measurements were due to Cu-K∝ (1.54Ǻ) radiation. JCPDS –
diffraction data (1999) is used to obtain h, k and L values. The inter planar
spacing (d) values compared with d for basic magnesium manganese ferrite
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available in JCPDS indexing cards to establish the spinel structure of the
ferrites. The „d‟ values are used to calculate the lattice constant (a) using a
standard method [1, 2]. The values of lattice constant were computed from
the extrapolation curves of lattice constant versus error function.
4.5 Density and porosity
The bulk density (d) of the samples was obtained using Archimedes
principle. The standard method was described by Smith and Wijn [3] and the
following relation gives bulk density (d).
d=
Weight of Sample in air
loss of weight of sample in water
The density (dx) of the samples, from XRD data is calculated from the
relation.
dx =
8M
Na 3
4.1
Where, M = molecular weight
N = Avogadro‟s number (6.023x 1023 molecules per mole)
Α = Lattice constant
The percentage of porosity of the sample is calculated by using the
relation.
% porosity = [1-
d
] x 100
dx
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4.2
4.6 Scanning Electron Microscope
The scanning Electron Microscope (SEM) is a good technique for
studying the morphology and microstructure of the materials. When the
material is focused by fine beam of electrons, it interacts with the atoms of
the specimen, resulting in release of secondary electrons. The samples were
freshly fractured; a small piece of each specimen was taken. Before making
grain size measurements a thin layer (400 Ǻ) of gold was deposited on the
etched surface of the material to avoid charging problem. JOEL, JSM
6610LV model Scanning Electron Microscope available at Advanced
Analytical Labaratories Andhra University, Visakhapatnam.
The average grain size is calculated from the relation [4]
Dg =
S
1 N
4.3
2
Where S = Area of cross section of micrograph, 1 = linear
magnification. N = No. of grains in the sections.
4.7 Vibrating Sample Magnetometer
The model of the vibrating sample magnetometer (VSM) was EG &
155 at ACMS, IIT-KANPUR, A typical block diagram of the vibrating
sample magnetometer set up is shown in the figure.
The working principle of the VSM is based on the faraday‟s law of
induction [5]. When a magnetic material is placed in a uniform magnetic
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field, a magnetic dipole moment is induced in it. If the sample is subjected to
sinusoidal frequency an electrical signal is induced by suitably located
stationary pick up coils. When the signal is at a frequency proportional to
that of the vibration amplitude due to magnetic moment then the effect can
be neutralized by generating another „Comparison‟ signal from a vibrating
capacitor and by coupling both these signals. The Vibrating Sample
Magnetometer as shown in the figure.4.2.
Fig. 4.2 shows the black diagram of VSM
The sample is mounted at the lower and of a slender vertical rod and is
centered in the region between the pole pieces of an electromagnet. The
upper and of the rod is fixed with a transducer assembly that converts a
sinusoidal α.c. drive signal provided by an oscillator/ amplifier circuit into a
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sinusoidal/ vertical vibration of the sample rod. The sample is thus made to
undergo a sinusoidal motion in a uniform magnetic field. The coils that are
mounted on the pole pieces of the magnet, pick up the signal resulting from
the motion of the sample. A standard nickel sample provided with the
instrument and having a saturation magnetization of 49.51 emu was used for
calibration. The saturation magnetization is calculated using magnetic
moment value from the relation.
Saturation magnetization =
Saturation magnetic moment
Value of the sample
4.8 Experimental setup for Curie temperature measurement
The techniques were employed for the measurement of Curie
temperature in the investigations. The Curie temperature (Tc) is nothing but
the transition temperature at which the ferromagnetic state of the material
changes to paramagnetic state. This principle was employed to determine the
Curie temperature is shown in figure. A small piece of ferrite sample is
attached to the lower end of an iron rod and the upper end of which is placed
vertically in contact with a pole piece of permanent electromagnet. The
lower end of the iron rod along with the sample was enclosed in a furnace
having a thermocouple for monitoring temperature. The temperature of the
furnace is gradually increased till the ferrite sample losses its magnetization,
falls due to gravity. The temperature at which the sample falls is taken as T c.
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Another method adopted was differential scanning calorimeter (DSC)
technique. Differential scanning calorimeter is a thermal analysis technique
that is used to measure temperatures and corresponding heat flow associated
with phase transactions in the material. Modulated DSC 2910 model was
used to determine Curie temperature and in shown in the figure. Thus heat
capacity and Tc were measured. Rath et al. [6] also adopted this method to
study the polycrystalline material.
4.9 Initial Permeability
Variation of initial permeability of the ferrite materials with frequency
in different ranges was determined by measuring inductance of the material
adopted by Beck [7]. Ferrite samples in the form of toroid of outer diameter
1.49 cm were used. The 30 SWG enameled copper wire with 30 turns
winding was used on these toroids. The inductance (L) was measured using
Hewlett Packard LF4192A impedance analyzer (5Hz to 13 MHz). The
impedance analyzer is shown in the figure. Initial permeability is calculated
using the formula
µ=L/L0
4.4
OD 
-9
Where L0 = 4.6 N2 log 
 t x 10 , Henry is the air core inductance,
 ID 
OD = Outer diameter, N = No of turns,
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ID = Inner diameter and t = thickness of the sample.
Initial permeability at room temperature was measured as a function
of substituent concentration (x) and frequency. The goal in designing the
LF4192A is accomplished due to an automatic LCR instrument and high
grade signal generator.
4.10 Hysteresis Loops
Hysteresis loops for ferrite material were traced at room temperature.
Image tracing was performed with an automatic hysteresis loop tracer called
i-magetronics. The experimental set up the loop tracer is shown in the figure.
The principle and functioning of the loop tracer was described by Likhite et
al. [8].
4.11 Resistivity measurement experimental setup
D.C. resistivity of the ferrite materials in the bulk form was measured.
A conductivity cell was used to study the variation of electrical
resistivity/conductivity with temperature. Diagram of this conductivity cell
is shown in the figure.4.3.
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Fig. 4.3. shows the scemetic cell of conductivity.
The cell consists of a metal frame with necessary arrangement for
holding the sample. The sample in the shape of pellet is freshly ground and
coated with silver paste to ensure good ohmic contact in between the two
electrodes of the cell, which could be pressed with spring. The experimental
set up is shown in figure. The temperature near the sample was measured by
placing a thermocouple close to it. Resistivity of a specimen can be
evaluated using the following formula.
P = R (A/d)
4.5
Where, A is the area of cross section and d is the thickness of the
pellet.
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4.12 Experimental setup for dielectric constant measurement
Dielectric studies of samples as a function of frequencies from 5 KHZ
to 13 MHZ were performed by measuring the capacitance with Hewlett
Packard 4192A impedance analyzer, using the expression,
oA)C
4.6
Where ε is dielectric constant, A is the area of the cross section, is
thickness of the sample, and ε0 is the permittivity of the free space
(ε0 =8.854 x 10-12 Fm-1).
The dissipation (D) was measured directly from the impedance
analyzer. The dielectric loss factor tan   , is also obtained.
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References
[1]
B. D. Cullity, Elements of X-ray diffraction, Addison – Wesley publishing co.
Inc. USA (1967).
[2]
A. R. Verma and O.N. Srivastava, Crystallography for solid State Physics, Wiley
Eastern Ltd., New Delhi, India (1982).
[3]
J. Smit and H.P.J. Wijin, “Ferrites”, Phillips Tech. Library Eindhoeven (1959)
144.
[4]
A. Globus, P. Duplex and M. Guyot, IEEE Trans., MAG-7 (1971) 617.
[5]
S. Foner, Rev., of Scientific Instruments, 30, p-548.
[6]
Rath, C., Mishra, N.C., Anand S., Das, R.D., Sahu, K.K., Upadhyay, C., Verma,
H.C., Applied Physics Letters, Vol. 76, No.4 p. 475-7 (Jan-2000).
[7]
Dr. Ing Carl Beck, „Magnetic material and their applications‟, Butterworths,
London (1974).
[8]
S. D. Likhite, C. Radhakrishna Murthy and P.W. Sahasrabudhe, The Review of
Scientific Instruments, 36 (1965) 1558.
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