chapter 4 suniya m
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Chapter 4 Results and Discussion
4.1 Introduction
The basic aim of this research work is the preparation of magnesium iron oxide thin films by
electrodeposition route, which is more preferable over the physical methods being a simple,
fast and inexpensive technique !, "#$
%pinel ferrites are very important magnetic materials because of their interesting magnetic
properties combined with chemical and thermal stability$ &agnesium 'ron (xide, also known
as magnesium ferrite whose study has been a motivating sub)ect due to its promising
properties$ &agnesium 'ron (xide *&g+e"(4 has inverse spinel structure$ Displacing of iron
with magnesium *ionic radius of -" fm in cubic inverse spinel structure further enhances the
magnetic properties ., 4#$
'n order to produce oxide/s thin films, 'n0situ oxidation has been carried out$ (xidation time,
an important parameter in electrodeposition technique has been varied to achieve the desired
properties of magnesium iron oxide thin films$ 1 series of six samples has been prepared with!2 minutes deposition and in0situ oxidation was carried out for 2, !3, !2, "3, "2 and .3
minutes, keeping the potential difference " $ 1ll the samples were deposited at room
temperature and without magnetic stirring of electrolyte$ 'n order to investigate the properties
of samples, samples were characteri5ed using various experimental tools$ The structural and
magnetic properties were investigated by 6RD and %& respectively$ The results obtained
are discussed in the following sections$
4.2 X-Ray Diffraction Analysis
60ray diffraction was used for the structural analysis of the thin films, deposited on copper
substrate$ 7ruker D8 1dvance Diffractometer with Cu09: radiation of wavelength !$243;3 values .!$-"A, ."$"8A, 4$82A, 23$!.A, .$"2A and .$8!A,
are corresponding to *4!!, *4"3, * 6 "", *-!! and *
4 .! planes of iron oxide *+e"(.
as matched with BC=D% card no$ !;0;2.$ 1t this oxidation time magnesium ferrite compound
is poorly formed$
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Figure 4.!'ndexed 6RD pattern of as0deposited thin film with !2 minutes oxidation$
The pattern with oxidation time of "3 minutes is shown in +igure 4$4$ 'n this pattern two
peaks of &g+e"(4appeared at "> values of 4.$!;A and -.$82A, corresponding to *433 and
*;"3 planes are matched with BC=D% card no$ !-04;$ Two peaks of iron oxide *+e "(.
appeared at "8$.-A and 23$!.A, corresponding to planes *3.! and *-!! are matched with
BC=D% card no$ !;0;2.$
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Figure 4.4'ndexed 6RD pattern of as0deposited thin film with "3 minutes oxidation$
The pattern with "2 minutes oxidation is shown in the +igure 4$2$ The diffraction peaks of
magnesium iron oxide at "> values of 4.$!;A, -.$82A and -4$!.A corresponding to *433, *2..
and *;"3 planes have appeared$ These 7ragg reflections are conspicuous and are correspond
to spinel structure$ The diffraction peaks at "> value of 23$!.A is corresponding to *-!! plane
of iron oxide *+e"(. as matched with BC=D% card no$ !;0;2.$ 1t this oxidation time
magnesium ferrite is richly formed$ The background noise and broadness of the peaks are
characteristic of particles with nanometer dimensions$ This happens because in the nano0
si5ed particles there are insufficient diffraction centers that cause the line broadening 2#$
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Figure 4."'ndexed 6RD pattern of as0deposited thin film with "2 minutes oxidation$
The pattern with oxidation time of .3 minutes is shown in +igure 4$;$ The pattern shows the
7ragg reflections peaks of &g+e"(4, appeared at "> values of 4.$!;A, .3$;3A and -4$!.A,
corresponding to *433, *""3 and *2.. planes of the spinel magnesium ferrite as matched
withBC=D% card no$ !-04;$ The diffraction peaks of iron oxide *+e "(., appeared at ."$2;A,
.$2.A and 23$!.A, corresponding to planes *4"3, * 4
.! and * 6
"" are matched with
BC=D% card no$ !;0;2.$
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Figure 4.#'ndexed 6RD pattern of as0deposited thin film with .3 minutes oxidation$
1ll samples have shown the most preferred orientation *433 of magnesium iron oxide in
addition to its other *""3, *2.. and *;"3 prominent reflections$ ariation in oxidation time
has caused the change in the crystallinity and purity of magnesium iron oxide thin films$
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Ta$le 4.1attice constant *a, unit cell volume *cell, crystalline si5e *D, 60ray density
*dx, dislocation density * and strain of as0deposited thin films with varying the oxidation
time$
%ample
&o.
'(idatio
n Time
)min*
+attice
constan
t
),*
nit cell
olume
),*!
X-ray
density
)g cm-!*
/rystalli
ne si0e
)nm*
Dislocatio
n density
)1(11"
m-2*
%train
)1(1-!*
! 2 8$.8 23$!; 4$23 !8$ "$-- $"4
" !3 8$.8 23$!; 4$23 !8$ "$-- $"4
. !2 8$.2 28"$!8 4$2; ".$-4 !$-- -$.8
4 "3 8$.; 28;$!; 4$2. !8$ "$-- $".
2 "2 8$.; 28;$!; 4$2. "!$3 "$3 -$
; .3 8$.2 28"$!8 4$2; !8$ "$-- $!
4.2.2 ariation in +attice 3arameter ith '(idation Time
attice parameters Ea/ for all electrodeposited thin films of cubic magnesium ferrite are
calculated using 7ragg/s equation *Fq$ 4$!$ The obtained values of lattice parameters *a for
all deposited films are in agreement with BC=D% card no$ !-04;$
a=dhklh2+k2+l2(4.1)
The trend of lattice parameter variations with oxidation time is shown in +igure 4$-$ Gith the
increase in oxidation time lattice parameter decreases$
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Chapter 4 Results and Discussion
Figure 4.5ariations in lattice parameter as a function of oxidation time$
4.2.! ariation in /rystallite %i0e ith '(idation TimeThe average crystallite si5e *D were determined using Debye %cherrer/s formula *Fq$ 4$"$
D= 0.9
cos *4$"
Ghere D is the average crystallite si5e of the phase under investigation, H is the wavelength
of Cu 9:used in 60ray diffraction, I the +ull width at half maxima *+GJ&, contribution to
the diffraction peak width due to small si5e of crystallites and must be taken in radians and >
is the 7ragg/s angle of diffraction 8#$
The average crystallite si5es *D of all the electrodeposited thin films with varying the
oxidation time are listed in Table 4$!$ The trend of crystallite si5e of as0deposited films with
the variation in oxidation time is shown in +igure 4$8$ The film oxidi5ed for !2 minutes has
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Chapter 4 Results and Discussion
shown the highest crystallite si5e, whereas the films oxidi5ed for 2, !3, "3 and .3 minutes
have shown comparatively small crystallite si5es$
Figur
e 4.6ariations in crystallite si5e with oxidation time$
4.2.4 ariation in Dislocation Density ith '(idation Time
The dislocation density indicates the amount of defects in a crystal$ 't is defined as the length
of dislocation lines per unit volume of the crystal$ 't is calculated by using the equation 4$.$
=
1
D2 *4$.
Ghere, D is crystallite si5e$ Jigher value of dislocation density indicates lower crystallinity
levels of the films ;#$ The dislocation density of all deposited thin films with varying
oxidation time is listed in Table 4$!$ The effect of oxidation time on the dislocation density is
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Chapter 4 Results and Discussion
shown in +igure 4$$ The small value of dislocation density and good crystallinity is obtained
in the film oxidi5ed for !2 minutes$ The value of dislocation density for the thin films
oxidi5ed for 2, !3, "3 and .3 minutes has shown the lattice distortion in the structure$ The
presence of dislocations or defects during the deposition process may be due to micro0strain
present in the film -#$
Figure 4.7ariations in dislocation density with oxidation time$
4.2." ariations in nit /ell olume ith '(idation Time
The slightly decreasing trend of unit cell volume of magnesium ferrite with oxidation time is
shown in +igure 4$!3$ &agnesium ferrite has cubic structure so its unit cell volume is )ust
cube of lattice parameter$
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Chapter 4 Results and Discussion
Figure 4.1ariations in unit cell volume as a function of oxidation time$
4.2.# ariation in X-ray Density ith '(idation TimeThe 60ray density of thin films was estimated using Fq$ 4$4$
=1.66042A
V (4.4)
Ghere is unit cell volume and 1 is atomic weigth of number of atoms or ions in a unit cell
8#$ (ne unit cell of magnesium ferrite has ." oxygen ions, !; ferric ions and 8 magnesium
ions$ 60ray density of all the deposited thin films is shown in Table 4$!$ The variation in x0ray
density with oxidation time is shown in +igure 4$!!$ 't approximately remains constant for all
oxidation times$ The synthesi5ed films with !2 and .3 minutes oxidation, exhibit slightly
large x0ray densities$
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Chapter 4 Results and Discussion
Figur
e 4.11=lot between 60ray density and oxidation time$
4.2.5 ariations in %tress8%train ith '(idation Time
The strain of the films was determined using the equation 4$2$
d
d =
2 tan *4$2
Ghere I is +ull width at half maxima *+GJ& of the peak having highest intensity and it is
taken in radians and > is the 7ragg/s angle$ The origin of the strain is also related to the lattice
mis0fit which in turn depends upon the deposition conditions #$ The trend of strain with
varying oxidation time is shown in +igure 4$!"$ The synthesi5ed film with in0situ oxidation
time of !2 minutes has shown lowest strain as compared to all the other films$ %tressKstrain
plot shows decreasing trend with increasing oxidation time$
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Chapter 4 Results and Discussion
Figure 4.12=lot of stressKstrain as a function of oxidation time$
4.! %9 Results of :lectrodeposited Thin Films
The magnetic properties of &g+e"(4 thin films were analy5ed using vibrating sample
magnetometer$ 1nalysis was carried out at room temperature and &0J curves of the thin
films were obtained$
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Chapter 4 Results and Discussion
4.!.1 9agnetic Analysis of As-deposited 9agnesium Iron '(ide Thin Films
'n0plane room temperature &0J curves for as0deposited magnesium iron oxide thin films
with varying oxygen time are shown in +igure 4$!.$ 1s0deposited films have shown a mixed
behavior i$e paramagnetic and ferromagnetic$ +erromagnetic contribution is indicated by
open loop at low field strength while paramagnetic behavior is indicated by close loop at
relatively high field$ The mixed behavior of &0J curves indicates that grains are not fully
developed as shown in 6RD patterns of as0deposited thin films$ The mixed behavior
indicates that the films require further heat treatment$
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Chapter 4 Results and Discussion
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Chapter 4 Results and Discussion
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Chapter 4 Results and Discussion
Figure 4.1!&0J plots for as0deposited &agnesium 'ron oxide thin films with oxidation
time for *a 2mins *b !3mins *c !2mins *d "3mins *e "2mins *f .3mins
Fffect of oxidation time on the coercive field EJc/, saturation magneti5ation E&s/, remenant
magneti5ation E&r/ and squareness E&rK&s/ *the ratio of remenant magneti5ation to saturation
magneti5ation of as0deposited magnesium iron oxide thin films are listed in Table 4$"$ 't is
clear that the magnetic properties are changed by changing the oxidation time$
Ta$le 4.2 The variation of the Coercivity *Jc, saturation magneti5ation *&s, remanance
*&r and squareness *%L of as0deposited thin films with oxidation time$
%ample Depositio '(idation /oerciity 9agneti0atio Remananc %;uarenes
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Chapter 4 Results and Discussion
&o. n time)min*
time)min*
1(1-!
! !2 2 ""3$2- 3$8.4-; 3$3"48 "$"8" !2 !3 44-$8! 3$-4-; 3$3";84 .2$33. !2 !2 22;$28 3$;".! 3$3";2! 4"$48;4 !2 "3 $".. 3$;!32 3$34.!2 -3$;";2 !2 "2 !.4$8 3$;"". 3$3." ;4$!4; !2 .3 !-$84; 3$;3"83 3$34;!" -;$23.
4.!.2 :ffect of '(idation on %aturation 9agneti0ation of As-Deposited
Thin Films
%aturation magneti5ation E&s/ of as0deposited &g+e"(4thin films as a function of oxidation
time is shown in +igure 4$!4$ Gith increasing oxidation time a decrease in saturation
magneti5ation is observed$ 1 maximum saturation magneti5ation E& s/ is observed at 2
minutes oxidation time$ The magneti5ation in the magnesium ferrite was derived from the site
occupancy difference of +e.Mbetween tetrahedral and octahedral sites !3#$ (n the other hand,
the presence of the iron oxide species *+e"(. may be the responsible for a retardation of the
magnetic properties$ 'n this case saturation magneti5ation is not showing increasing trend
with the increase of the crystallite si5e$
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Chapter 4 Results and Discussion
Figure 4.14=lot of %aturation magneti5ation as a function of oxidation time$
4.!.! :ffect of '(idation on Retentiity of As-Deposited Thin Films
The effect of oxidation time on retentivity E& r/ of as0deposited thin films is shown in +igure
4$!2$ The values of retentivity vary randomly with oxidation time$ The film with 2 minute
oxidation time has shown the lowest value of remenant magneti5ation E&r/$
Figure 4.1"=lot of Retentivity as a function of oxidation time$
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Chapter 4 Results and Discussion
4.!.4 :ffect of '(idation on /oerciity of As-Deposited Thin Films
The coercivity EJc/ of a magnetic material is usually a measure of its magneto0crystalline
anisotropy !!#$ The coercivity of as0deposited thin films as a function of oxidation time is
shown in +igure 4$!;$ Coercive field of the films was increased up to the oxidation time of !2
minute and after that trend of coercivity was decreased$ 1 large increase in the coercivity for
the sample with oxidation time 2 minute could be attributed to a high intrinsic coercive force
of iron oxide *+e"(. solid !"#$ The value of coercivity varies randomly$ This change may be
due to the low crystalline anisotropy, which arises from crystal imperfection and the high
degree of aggregation !!#$
Figure 4.1#=lot of Coercivity as a function of oxidation time$
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4.!." :ffect of '(idation on %;uareness of As-deposited Thin Films
The squareness also known as remanant ratio RN &rK&s shows the ease with which the
direction of magneti5ation reorients to the nearest easy axis direction after the field is
removed$ The small value of R indicates the isotropic nature of the sample !.#$ The
squareness of as0deposited thin films has shown almost increasing trend with increasing
oxidation time as shown in +igure 4$!-$
Figure 4.15=lot of %quareness as a function of oxidation time$
4.4 9agnetic Analysis of 9agnetically Annealed 9agnesium Iron '(ide
Thin Films
The deposited thin films of magnesium iron oxide were annealed at .33 C *in presence of
magnetic field for one hour$ &0J loops of annealed thin films were observed to show the
ferromagnetic behavior that might be expected due to the change in crystalline state of films$
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Chapter 4 Results and Discussion
7y annealing the film with 2 minutes in0situ oxidation, still a mixed behavior wit dominant
ferromagnetic behavior was observed$ Thin film with 2 minutes oxidation showed very
different behavior than other samples, as easy axis was observed along the out0plane field as
shown in +igure 4$!8$ The difference between the &0J curves for in and out0plane field was
observed describing the uniaxial magnetic anisotropy$ The magnetic anisotropy is a factor
which strongly affects the shape of the hysteresis loop$ The magnetic properties are direction
dependent$ +or an anisotropic material the magnetic moments line up in the direction of easy
axis of magneti5ation, while in an isotropic material the magnetic moments have no preferred
direction for orientation$ Fasy axis is an energetically favorable direction of spontaneous
magneti5ation and depends on the cause to raise magnetic anisotropy$ 1nisotropy can be
magneto0crystalline anisotropy, shape anisotropy, exchange anisotropy and magneto0elastic
anisotropy$ The annealed films have shown strong ferromagnetic behavior with relatively
high value of coercivity$
&0J plot for the electrodeposited magnetically annealed thin film of in0situ oxidation of !3
minutes at potential of " is shown in +igure 4$!$ The hysteresis curves for both applied
fields perpendicular *out0plane and parallel *in0plane are not symmetric about the axis and
showed a shift on the magneti5ation axis that is because of anisotropy$ The &0J curve has
shown coercivity of 4."$.! and ;.$-. O for in0plane and out0plane respectively$
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Chapter 4 Results and Discussion
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Figure 4.16&0J curve of magnetically annealed thin film of 2 minutes oxidation$
Figure 4.17&0J curve for magnetically annealed thin film of !3 minutes oxidation$
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Chapter 4 Results and Discussion
&0J loop for the electrodeposited magnetically annealed thin film of in0situ oxidation for !2
minutes is shown in +igure 4$"3$ The &0J curve for in and out0plane has shown that & sis
larger in case of in0plane as compared to out0plane$ The in0plane &0J curve has shown
coercivity of .!;$42 O and out0plane curve shows 433$!" O$
Figure 4.2 &0J curve for magnetically annealed thin film of !2 minutes oxidation$
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Chapter 4 Results and Discussion
Figure 4.21 &0J curve for magnetically annealed thin film of "3 minutes oxidation.
Figure 4.22 &0J curve for magnetically annealed thin film of "2 minutes oxidation.
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Chapter 4 Results and Discussion
&0J curves for the magnetically annealed thin film of in0situ oxidation of "3, "2 and .3
minutes have shown an enhanced ferromagnetic behavior as shown in +igure 4$"!04$".$ This
modified magnetic behavior as compared to that of as0deposited thin films have pointed out
the existence of a metastable cation distribution which results in different exchange
interactions between themselves$The different exchange interactions have caused modified
magnetic properties !4#$ The &0J curves for in and out0plane has shown that &sin case of
in0plane was larger than that of out0plane$ &agnetic properties of magnetically annealed thin
films are summari5ed in Table 4$.$
Figure 4.2!&0J curve for magnetically annealed thin film of .3 minutes oxidation$
Ta$le 4.! The variation of the Coercivity *Jc, saturation magneti5ation *&s, remanance
*&r and squareness *%L of magnetically annealed thin films with oxidation time *t$
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Chapter 4 Results and Discussion
%ampl
e &o.
t
)min*
In-
plane
'ut-
plane
In-
plane
'ut-
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In-
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'ut-
plane
In-
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'ut-
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8
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3$""2
8
4.4.1 ariations in /oerciity of Annealed Thin Films ith '(idation Time
Ghen the samples were placed in0plane to magnetic field, coercivity *J c decreased with the
increasing oxidation time as shown in +igure 4$"4 but when oxidation rate was increased
from !2 minutes samples have shown again increasing trend in coercivity$ The films which
were oxidi5ed for 2 minutes have shown higher value of coercivity for in0plane, while same
samples were placed out0plane in external magnetic field have shown lower value of
coercivity$ The variation in coercivity would be due to change in crystalline state of the films
after annealing$
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Chapter 4 Results and Discussion
The coercivity of the films strongly depends on grain si5e, microstructure of films and
residual magnetic induction along with other complex factors$ The coercivity of the films is
also strongly dependent on magneto0crystalline anisotropy !;#$
Figure 4.24Jcplot of annealed films with oxidation time
4.4.2 ariations in %aturation 9agneti0ation of Annealed Thin Films ith
'(idation Time
%aturation magneti5ation *&s of annealed films has shown an increasing trend with oxidation
time$ %aturation magneti5ation in case of in0plane is larger than out0plane as shown in +igure
4$"2$ The value of saturation magneti5ation depends upon crystallite si5e, oxidation time and
annealed temperature$
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Chapter 4 Results and Discussion
Figure 4.2" &s plot of annealed films with oxidation time$
4.4.! ariations in Retentiity of Annealed Thin Films ith '(idation Time
Retentivity E&r/ of annealed films has shown an increasing trend with increasing oxidation
time$ Retentivity in case of in0plane was observed to be larger than out0plane as shown in
+igure 4$";$
Figure 4.2# &r=lot of annealed films as a function of oxidation time$
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Chapter 4 Results and Discussion
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