Study of the physical properties of Co-Ti substituted rare ... · prepared by standard ceramic technique of Co-Ti substituted rare earth ferrite ... The ionic radii on A and B sites

Presented by

Abd Al-Salam Kurdey Al-Muhamady

(2012)

prepared by standard ceramic technique

of Co-Ti substituted rare earth ferrite

Study of the physical properties

A Thesis Submitted

to

Faculty of Science

In Partial Fulfillment of the

Requirements for Ph.D. Degree in

Physics

Department of Physics

Faculty of Science

Cairo University

ACKNOWLEDGMENT

I would like to express my deepest gratitude and thankfulness to Prof.

Dr. DSc. M. A. Ahmed, Materials Science Lab. (1), Physics Department,

Faculty of Science, Cairo University, for suggesting the point of search and

supervision me during the work. It is useful and suggestions, fruitful and scientific

discussion, continuous encouragement, and valuable help during the performance of

this thesis. Many thanks to Dr. Khaled Elsayed, and Dr Hisham Imam for them

continuous guidance and support during the progress of the thesis. Special thanks

for my friends ,Dr Ali Azab, M.Afify, and A. Karmaly for supporting me in my

research project.

I would also like to thank Dr. Samaa Imam El-Dek, and all friends at

the Materials Science Lab (1) (MSL(1)), who provided me with invaluable

laboratory and life skills. Also all thanks to Physics Department, Faculty of

Science, Cairo University, for their encouragement during the progress of this

work.

Finally, and most importantly, I would like to thank my family. My father

and my brothers and sisters .Special thanks to my wife and my sons

Signature

A.Almuhamady

I

The samples under investigation of the general formula:

Co1+xTixFe2-2xO4, where

0 ≤ x≤0.7, Co1+xTixRyFe2-2x-yO4 , x=0.1,Ry =Gd,

,0.01 ≤ y≤0.04 and Co1+xTixRyFe2-2x-yO4 ,x=0.1,Ry =Er ,Nd ,Ho and Ce , y=0.02

were prepared using the standard ceramic technique. FTIR and X-ray

diffraction were carried out to assure the formation of the samples in the

proper form. Magnetic susceptibility of the samples was carried at

different temperature as a function of magnetic field. The dielectric

properties for the prepared samples were measured at different temperature

as a function of frequency. Also we use seebeck effect to determine the

majority type of our samples if its p-type or n-type.

1-Prof. Dr. D.Sc. M.A. Ahmed

Professor, Physics Department,

Faculty of Science, Cairo University.

Physics Department, Faculty of

National Institute of Laser Enhanced Sciences,

NILES, Cairo University.

II

ABSTRACT

Signature:

Science, Cairo University.

3-Dr. Hisham Imam

Signature:

2- Dr. Khaled Elsayed.

Signature:

Supervisors:

, Co1+xTixFe2-2xO4, 0 ≤ x≤0.7, Co1+xTixRyFe2-2x-yO4 تم تحضير العينات ذات الصيغة

,0.01 ≤ y≤0.04 and Co1+xTixRyFe2-2x-yO4 ,x=0.1,Ry =Er ,Nd ,Ho and Ce , y=0.02

x=0.1,Ry =Gd تكون العينات فقد تم اجراء كل من باستخدام طريقة السيراميك التقليدية وللتأكد من

وتم قياس قابلية (FTIR) وكذلك التحليل باستخدام االشعة تحت الحمراء (X-ray) حيود االشعة السينية

المحضرة عند درجات حرارة مختلفة كدالة تحت تاثير ( للعينات Magnetic susceptibility) التمغنط

وكذلك حساب ( Hysteresis loop) مجال مغناطيسي خارجي اضافة الى منحنى التخلف المغناطيسي

لكل عينة اضافة الى حساب المغناطيسية ( saturation of magnetization) قيمة التشبع المغناطيسي

تم تعيين ما ( seebeck effect) سيبك تأثيرباستخدام و .( Remnant magnetization) المؤثرة

ام فجوات وعند درجات حرارة مختلفة, اضافة الى ذلك فقد تمت اذا كانت حامالت الشحنة الكترونات

وتحت تأثيرللعينات في درجات حرارة مختلفة (dielectric properties) دراسة الخواص الكهربية

مختلفة . ترددات

توقيع السادة المشرفون:

كلية العلوم استاذ الفيزياء التجريبية

جامعة القاهرة كلية العلوم/جامعة القاهرة

د/هشام امام -3

/جامعة القاهرةالمعهد القومي لعلوم الليزر

الولخص

"دراسة الخواص الفيزيائية للكوبالت- تيتانيوم فيرايت والوطعن

بعناصر ارضية نادرة وهحضر بتقنية السيراهيك التقليذية"

1- أ.د محمد علي احمد 2- د/خالد عبد الصبور

APROVAL SHEET FOR SUMISSION

Professor, Physics Department, Physics Department, Faculty of

3-Dr Hisham Imam

National Institute of Laser Enhanced Sciences,

NILES, Cairo University

Thesis Title:

Study of the physical properties of Co-Ti

substituted rare earth ferrite prepared by standard

ceramic technique

Name of candidate: Abd Al-Salam Kurdey Al-Muhamady

This thesis has been approved for submission by the

supervisors:

Signature:

Prof. Dr. Omar osman

1- Prof. Dr. D.Sc. M. A. Ahmed 2-Dr. , Khaled Elsayed.

Faculty of Science, Cairo University. Science, Cairo University

Signature: Signature:

Chairman of Physics Department

signature:

CHAPTER ONE INTRODUCTION

1

Chapter One

A : Literature Survey

This Chapter discusses the theory and background of this work and, thus,

elaborates on the work that has been done so far in studying the physical

properties of ferrite materials. The Chapter is mainly concerned with the

magnetic and electrical properties of such materials.

J. Bursik

(1) studied pure Co, and Ti-substituted hexagonal barium ferrite

12 19

minutes in an oxygen atmosphere, polycrystalline films with a thickness of 1–

x x 12-2x 19

were measured in the range from 500 to 2500 nm at room temperature. The

absorption coefficient did not display much structure, but specific Faraday

rotation spectra of Co, Ti-ferrite films showed local maxima at 720, 1475 and

1750 nm. At those wavelengths, the magneto-optical figure of merit attains its

maximum values. For comparison of the crystallization and magnetic properties,

Ba(CoTi)xFe12-2xO19 (x=0.9) powder has also been prepared by the sol-gel

method.

Vasambekar et al

(2) studied polycrystalline compounds of the series

CdxCo1-xFe2-yCryO4 .x . 0, 0.25, 0.50, 0.75 and 1.00; y . 0, 0.15 and 0.30). were

prepared by a standard ceramic technique. The crystallographic data were

obtained using X-ray diffraction. All the compounds were found to have f.c.c.

(BaFe O , BaM) films prepared by the dip-coating method from

1.8 µm on SiO2 substrates were obtained. Spectral dependencies of the Faraday

rotation and the optical transmission of BaCo Ti Fe O (0.0 ≤ x ≤0.8) films

oalkoxides. After repeated dipping, drying and calcining at 500 C for about 15


2

symmetry. The ionic radii on A and B sites .rA andrB, respectively. and the

bond lengths on A and B sites (A±O and B±O, respectively) were calculated.

The values of rB and B±O were found to be greater than rA and A±O, except for

the Cd and Cr3+

substituted Cd ferrites. The d.c. electrical resistivity of pelletized

samples was calculated by measurements of voltage and current using a two-

probe method at various temperatures. The values of Curie temperatures .Tc.

observed in d.c. resistivity measurements, for all the composition under

investigation, were found to be in good agreement with those observed in

energies .DE. were found to be higher in the para-region than in the ferri-region.

The resistivity of the samples is found to be dependent on the saturation

magnetic moments .nb . of the samples. The resistivity of Co ferrite is found to

be higher than that of Cd ferrite at 475 K.

M. Fayek et al (3)

studied the conductivity of manganese cobalt ferrite in

the low frequency range. The samples are of chemical formula CoMnxFe2-xO4,

0≤x≤1. The frequency range is 102 to 10

5 Hz and temperature range 300 to

950K. The obtained results reveal the existence of a sum of two conductivity

parameters dc , H where the first is the DC conductivity which is mainly due

to excitation of electrons in localized states to the conduction bands. The authors

found that the dependence of conductivity on frequency decreases with

increasing temperature and at high temperature it becomes frequency

independent.

L. Rad et al.(4)

studied the effect of chromium impurity on the DC

resistivity of Lithium antimony ferrite. The lattice parameter was found to

decrease with increasing Cr ion substitution. The room temperature DC

resistivity was found to increase with x, this has been attributed to electron

hopping and cation substitution. The variation of resistivity with temperature

o

susceptibility measurements and by the Loria&Sinha technique. The activation


3

showed a change in slope for all the samples. There are two different regions of

different activation energies. The decrease of lattice parameter with increasing

Cr3+

ion due to the fact that Cr3+

has ionic radius of 0.64 oA that replaces 0.67

oA. The increase of DC resistivity by increasing Cr3+

ion is due to Verway

conduction mechanism that involves exchange of electrons between ions of the

same element present in different valance state, and distributed randomly over

crystallographically equivalent lattice site.

S.A. Mazen(5)

studied the electrical conductivity and thermoelectric

power for the mixed Cu-Ti ferrite Cu 1-xTixFe 2O4 with x=0 to 0.5 with

temperature range from 300 to 773 K . It was found that all compositions behave

as n-type semiconductors in the measured range of temperatures. The

conduction mechanism was discussed on the basis of a small-polaron hopping

model. The activation energy from the conductivity data was found to be higher

than that calculated from the thermoelectric power . The discrepancy between

them is evidence for the existence of thermally activated hopping in the ferrite

system.

M. El-Sadawy et al (6)

studied the system Co0.6Zn0.4MnxFe2−xO4,prepared

by the ceramic method. The dielectric constant, electrical conductivity and

magnetic susceptibility were studied as a function of the jump length of

electrons at the B sites of the above compositions. The increase of the jump

length of electrons increase the electrical conductivity, dielectric constant and

magnetic susceptibility which confirms that the jumping of electrons is

predominant in the electrical behavior of ferrites.

S. A. Mazen(7)

studied the structure and formation of the two systems of

mixed ferrites Cu1+xGexFe2−2xO4 and Cu1+xTixFe2−2xO4 (where0≤ x ≤ 0.4) using

X-ray diffraction (XRD) and IR absorption analysis. The samples of x = 0

(CuFe2O4) and x = 0.1 of Cu–Ti system were formed in tetragonal structure. All


4

other samples of the two systems were formed in cubic symmetry with constant

lattice parameter. For Cu–Ge ferrite the lattice parameter (a) equals 0.837 nm

while it equals 0.840 nm for the system of Cu–Ti ferrite. The IR spectra show

two main absorption bands ν1* and ν2

*. The band ν1

* has a constant value

570 cm−1

for the two systems. The position of ν2* is around 400 cm

−1 and

slightly increasing with the increase of Ge or Ti content. It was found that the

threshold energy corresponding to the threshold frequency for the Cu–Ge ferrite

is about 0.103 eV, but for the Cu–Ti ferrite is bit lower, about 0.098 eV. The

thermoelectrical power shows that CuFe2O4 and Cu1.1 Ge0.1Fe1.8 O4 behaves as

an n-type semiconductor, but the other composition of the two systems of both

ferrites behave as p-type semiconductor at around room temperature.

B.P. Ladgaonakar et al.(8)

studied the structural and DC electrical

resistivity of Nd3+

substituted Zn-Mg ferriteof the formula ZnxMg1-xFe2-yNdyO4,

0 ≤ x ≤ 1 ; y = 0.0, 0.05, and 1. The DC electrical resistivity was obtained by

current measurement for fixed voltage supply in the temperature range from

room temperature to 750 oC using two-probe method. The author found that the

tetrahedral radius increases with increasing Zn2+

concentration and that of

octahedral decreases. This is attributed to the large ionic radius of Zn2+

ions

(0.75oA) for composition y =0.05, and 0.1 the Nd

3+ substitution. The author

found that the temperature dependence of the conductivity obeys Arrhhenius

relation, which is attributed to the hopping of electrons between multiple

valance iron ions. The resistivity was found to increase on Nd3+

substitution this

is because Nd3+

does not change valancy and so does not participate in

conduction mechanism.

M.A. Ahmed et al(9)

. investigated the real part of the dielectric constant

ɛ/ as well as the ac resistivity of the rare earth ferrite Li0.5+zYbxCozFe2.5-z-xO4,

0.0 ≤ x ≤ 0.2, z = 0.1 were measured at different temperatures (300-800K) as a

function of frequency (10 kHz-5 MHz). More than one hump was obtained due


5

to the presence of different polarization processes and conduction mechanisms.

The obtained data were discussed on the basis of the valence exchange between

(Fe3+

, Fe2+

), (Fe2+

, Yb3+

) and (Fe3+

, Co2+

). The values of the activation energy

indicate the semiconducting properties of the investigated samples. Theoretical

fitting was carried out for the samples with different Yb concentrations and the

reported data were found to be typical. The interaction mechanisms for the

samples under investigation have been studied in the temperature range (300-

800 K).

M.A. Ahmed et al(10)

. studied the X-ray diffraction, the real part (ɛ/), the

imaginary part (ɛ//) of dielectric constant, and the molar magnetic susceptibility

(χM) for Mg1+xTixFe2-xO4 ferrite (0.1≤ x≤ 0.9) were studied. The date of X-ray

diffraction showed that the unit cell parameter increases with Ti concentration

and ascribed to the predicted variation of the cation distribution, while Mg2+

ions are highly diffusible and very sensitive to heat. The effect of dilution by Ti

ions is discussed in terms of increasing superparamagnetic and single domain

(SP/SD) grains. The measurements of ɛ/ were performed at different

temperatures as a function of frequency, while the magnetic susceptibility was

studied at different magnetic field intensities. The variation of the dielectric

properties depends mainly on the valence exchange between the different metal

ions in the same site or in different sites. All parameters such as ɛ/, ɛ

//, χM

showed a decrease in value with increasing Ti and Mg concentration. The

dispersion in ɛ/ with frequency disappeared gradually with increasing Ti

concentration.

M. A. Ahmed et al

(11) studied the dependence dielectric behavior of Mn-

Zn ferrite on sintering temperature. The dielectric constant of Mn-Zn ferrite was

measured at different temperature and frequencies as a function of sintering

temperature ranging from 1200°C to 1400 oC at heating rate of 6

oC/min. The

resistivity and Seebeck coefficient were measured in the same range of


6

temperature as that of dielectric measurements. More than one type of

polarization is expected to vary the dielectric constant. Hoping mechanism was

the predominant one in conduction processes. The authors found that the relative

dielectric constant increases with increase of sintering temperature. It is found

that as the frequency increases the relative dielectric constant decreases due to

decrease in the polarizability at all sintering temperature. The minimum Curie

temperature is found at 480 oC for the sintering temperature 1300

oC. Form the

values of Seebeck coefficient the ferrite system is p-type for all samples. The

author concluded that the increase in relative dielectric constant with applied

frequency is due to the cooperation of different types of polarization, namely

orinational and rotational polarization as well as the electron hopping between

Fe2+

and Fe3+

. The existence of shoulder at 580 K indicates the migrational and

Maxwell Wagner polarization.

K.K. Patankar et al.(12)

studied the composites XBa0.8Pb0.2TiO3–

(1−X)CuFe2O4, in which X varies as 0.5 ≤ x≤ 1 prepared by ceramic method.

The presence of the two phases has been confirmed by XRD. Variation of

dielectric constant (έ) with temperature at various frequencies has been studied.

Two peaks are observed in dielectric constant versus temperature plots, which

are assigned to ferroelectric phase transition and the other to copper ferrite phase

transition (tetragonal–cubic). It is also noted that ferrite phase shows relaxation

behaviour. All the samples show linear magnetoelectric effect in the presence of

static magnetic field. The maximum value of magnetoelectric conversion factor

(dE/dH) was found to be 230 (μV cm−1

Oe−1

) in the composite with composition

X=0.7.

M. A. Ahmed et al.(13)

studied the effect of Ti on the magnetic and

dielectric properties of the Mg-ferrite. The author found that the variation of the

dielectric properties depends mainly on the valence exchange between the

different metal ions in the same site, or in different sites. All parameters such as


7

real and imaginary parts of the dielectric constant, showed a decrease in value

with increasing Ti and Mg concentration. The dispersion with frequency

disappeared gradually with increasing Ti concentration. The authors found from

the XRD data that for x = 0.7 to 0.9 the samples are not monophasic pure spinel

structure. The authors found that there is no magnetic moment ordering for the

sample with x = 0.7. They observed an increase in the unit cell parameter with

increasing Ti concentration. The Curie temperature is found to shift to lower

values gradually with increase of Ti concentration in the sample with x = 0.7

which is compatible with Monte Carlo simulation of Scholl and Binder that

shows a typical paramagnetic behavior, which is in a good agreement with the

X- Ray data.

M. Amanullah et al.(14)

studied the effect of Co substitution on the

magnetic and electrical properties of iron-deficient nickel-copper mixed ferrites

containing a small quantity of manganese oxide. The presence of Co enhances

the specific magnetization although the saturation magnetization falls a little due

to decrement of density. The initial permeability changes linearly with the

average grain size of the materials and shows fairly good thermal stability for

higher Co concentration. An appreciable increment in DC resistivity along with

decrement in dielectric loss factor at 100MHz can also be obtained for higher Co

concentration.

C.B. Kolekar et al.(15)

investigated polycrystalline compositions of soft

ferrite system, CdxCu1-xFe2-yGdyO4 (0 ≤ x ≤ 1; y=0.00, 0.10 and 0.30) were

prepared by standard ceramic method. X-ray diffraction study show formation

of single phase cubic spinel ferrite for the compositions X≥0.20 and tetragonal

nature for compositions X =0.0; for all values of Gd3+

(y=0.00, 0.10 and 0.30)

concentration. Saturation magnetization and magnetic moments were found to

be increased with cadmium concentration up to X =0.40; for all values of Gd3+

content, obeying Neel’s two sublattice model and decreases thereafter, showing


8

existence of non-collinear spin interaction. The Gd3+

substitution results into

reaction in the magnetic moments. This is due to occupancy of Gd3+

ion on

octahedral (B) site, resulting into dilution in the magnetization of B sublattices.

The Curie temperatures for all compositions are found to be decreasing with

substitution of Cd2+

concentration. This is attributed to the occupancy of

cadmium on tetrahedral (A) site, causing dilution in the inter site magnetic

interaction. The temperature dependence of AC susceptibility is also studied and

its behavior is explained on the basis of domain structure.

A Pandit et al. (16)

studied the samples of the series Co1+ySnyFe2–2y–

xCrxO4 ferrites with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and y = 0.05, were prepared by

the usual double sintering ceramic technique. The single-phase spinel structure

of the samples was confirmed by using X-ray diffractometry technique. The

lattice parameter ‘a’ with an accuracy of±0.002 Å were determined using Bragg

peaks of XRD pattern. The lattice parameter ‘a’ decreases with concentration, x,

which is due to the difference in the ionic radii of Cr3+

and Fe3+

ions. The X-ray

intensity calculations were carried out in order to determine the possible cation

distribution amongst tetrahedral (A) and octahedral [B] sites. The X-ray

intensity calculations show Cr3+

ions occupying B site. The saturation

magnetization, ss, and magneton number, nB (the saturation magnetization per

formula unit), measured at 300 K determined from high field hysteresis loop

technique decrease with increase in concentration, x, suggesting a decrease in

ferrimagnetic behaviour. Thermal variation of low field a.c. susceptibility

measurements from room temperature to about 800 K exhibits almost normal

ferrimagnetic behaviour and the Curie temperature, TC determined from a.c.

susceptibility data decreases with increase in x.

F.A. Radwan et al.(17)

studied the Mg1+‏xTixFe2-2xO4 samples prepared by

standard ceramic technique. The preference of Mg2+ ions to the octahedral site ‏

decreases the ratio of the normal spinel in the investigated ferrite where the


9

Mg +‏2

increases on the expense of the Fe+‏3

ions on the same site. The increase in

the conductivity was found to be due to thermally activated mobility of charge

carriers. The mobility data enhances the use of Verway model of conductivity

which depends on the electron exchange between iron ions of different valences

located on the same crystallographic sites. The existence of Ti+‏4

ions on the

octahedral site screens the polarization and decreases the conductivity of the

samples. Peculiar behavior was obtained for Ti content of 0.7 and 0.8 due to the

presence of secondary phases.


studied the rare earth doping effect on the

structural and electrical properties of Mg-Ti ferrite of the general formula

Mg1+xTixRyFe2-2x-yO4; x = 0.5, y = 0, 0.025 and R = (Nd, Gd and La). The

investigated samples were crystallized in the spinel phase. The measurements of

the electrical properties were carried out at different temperatures (295–750 K)

as a function of the applied frequency (50–1000 kHz). The experimental results

show that the rare earth ions initiate new sites called dodecahedral (C-sites) and

at the same time increase the valence exchange between the different metal ions

existing in the different sites. This behavior takes place at certain concentrations

of the rare earth ions. The low rare earth concentration as well as the high

sintering times (100 Hours) leads to an inflection in the electrical properties.

Verway conduction mechanism and hopping are used to interpret the

conductivity of the samples. The author concluded that introducing a small

amount of R2O3 instead of Fe2O3 leads to an important modification in the

electrical and structural properties of the sample. The activation energy of the

low temperature range are lower than those in the high temperature range. This

is due to the presence of more than one conduction mechanism. Seebeck

coefficient indicates that the charge carriers of the investigated samples are the

electrons and small polaron.


10

M.B. Kothale et al.(19)

studied the magnetoelectric (ME) composites of

Cu0.6Co0.4Fe2O4 +Ba0.8Pb0.2TiO3 prepared using a conventional ceramic double

sintering process. The presence of phases was confirmed by X-ray diffraction

(XRD). The variation of dielectric constant (έ) in the frequency range 100 Hz–

1 MHz with temperature was studied. The conduction phenomenon is explained

on the basis of small polaron hopping model. The confirmation of this

phenomenon is made with the help of AC conductivity measurements. The static

value of magnetoelectric conversion factor was studied as a function of intensity

of the magnetic field. The maximum value of ME coefficient was observed for

15% ferrite+85% ferroelectric phase.


studied the transport and magnetic properties of

Co-Zn-La ferrite. The dielectric constant and dielectric loss factor were

measured at different frequencies (100 kHz to 5 MHz) and different

temperatures (300-850 K). More than one type of polarization participates in the

dielectric process, Maxwell Wagner polarization is the one participating in the

high temperature region. The electrical conductivity measurement showed that

there is more than one conduction mechanism participating in conductivity. The

hopping mechanism either by holes or electrons or both is the predominant one.

The increase in conductivity is due to the thermally activated mobility and not to

thermal creation of additional mobile charge carriers. The replacement of Fe3+

by La3+

on octahedral sites and the presence of Co2+

as well as Zn2+

ions on the

tetrahedral sites, play a significant role in the electrical and magnetic properties

of the investigated samples. The values of the activation energy obtained

indicate the semi-conducting behavior of the investigated ferrite.

A.M. Abo El Ata et al.(21)

studied AC conductivity and dielectric

properties have been studied for a series of polycrystalline spinel ferrite with

composition CoAlxFe2−xO4, as a function of frequency and temperature. The

results of AC conductivity were discussed in terms of the quantum mechanical


11

tunneling and small polaron tunneling models. The dispersion of the dielectric

constant was discussed in the light of Koops model and hopping conduction

mechanism. The dielectric loss tangent (tanδ) curves exhibits dielectric

relaxation peaks which are attributed to the coincidence of the hopping

frequency of the charge carriers with that of the external fields. The AC

conductivity, dielectric constant, and dielectric loss tangent were found to

increase with increasing the temperature due to the increase of the hopping

frequency, while they decrease with increasing Al ion content due to the

reduction of iron ions available for the conduction process at the octahedral

sites.

H.M. Zaki et al.(22)

investigated two mixed copper ferrite systems,

Cu1+xGexFe2−2xO4 (system 1) and Cu1+xTixFe2−2xO4 (system 2) with 0 ≤ x≤ 0.4.

The two systems were prepared using the standard ceramic method. X-ray

analysis shows that both systems were formed in a single spinel phase except the

sample with x = 0.4 for the two system. Some of the magnetic properties were

measured, such as the initial permeability, magnetization and relative

permeability. It was found that the Curie temperature (TC) decreases from 714 to

542K for the first system while it decreases from 714 to 570K for the second

system. The cation distribution of the two systems was proposed. The sample

with x = 0 (CuFe2O4) shows the lowest magnetization value for both systems.

The behavior of relative permeability shows two regions for the first system and

three for the second system.

A.D. Al-Rawas et al (23)

investigated spinnel copper ferrites Cu1+xMxFe2-

2xO4 (M=Ge, Ti) with 0≤ x ≤ 0.4 using Mossbauer spectroscopy and magnetic

measurements. Mossbauer measurements performed at 77 and 300K show

broadened magnetic sextets superimposed on a paramagnetic doublet. The

magnetic components have been assigned to Fe3+

in two non-equivalent

crystallographic tetrahedral and octahedral sites. The Mossbauer data show that


12

Ge4+

has strong preference to occupy the tetrahedral site in contrast to Ti4+

which occupy the octahedral site. Saturation magnetization (MS) measurements

were performed using a vibrating sample magnetometer in the temperature

range of 77–750 K, while magnetic susceptibility (m) measurements were

performed using a Faraday microbalance susceptometer in the range of 500–

1000 K. Both MS and m variations with temperature indicate that the Curie

temperature TC decreases almost linearly with increasing Ti and Ge

concentrations. The magnetic moments calculated from the MS data and the

effective paramagnetic moments calculated from wm data are discussed on the

basis of Neel’s two sublattice molecular field model and the cations distribution

obtained from the Mossbauer analysis.

L. John Berchmans et al.(24)

studied the structural and electrical

properties of magnesium-substituted nickel ferrite having the general formula of

Ni1-xMgxFe2O4 (x=0, 0.3, 0.6, 0.9) as a function of magnesium ion

concentration. The materials have been prepared by citrate gel process using

metal nitrate salts as a cation precursors and citric acid as gelating agent. The

powder X-ray diffraction pattern confirms fcc structure for the synthesized

compound. The variation of lattice parameter and the tetrahedral radius

increases with increase in Mg2+

ion concentration. The AC electrical parameters

such as dielectric constant (ɛ\) and loss tangent (tan ŋ) for all the systems have

been studied as a function of frequency in the range 50 Hz to 10 kHz at room

temperature. A maximum DC electrical conductivity of 3.3 cm-1

was obtained

at a temperature of 1000 0C and a AC electrical conductivity of 10.94x10

-6 at 10

kHz was observed in the composition x = 0.6 i.e. for Ni0.4Mg0.6Fe2O4 compound

which may be due to the maximum Fe2+

concentration in the octahedral sites.

The dielectric constant follows the Maxwell’s–Wagner interfacial polarization

and the relaxation peaks were observed in the dielectric loss properties. The


13

FTIR spectra show the characteristic peaks of ferrite sample. The morphological

features were studied using scanning electron microscope.

M.M. Rashad et al(25)

investigated Nano-sized nickel ferrite powders

have been synthesized from fly ash via a chemical synthesis route, co-

precipitation method. X-ray diffraction analyses showed that pure crystalline

nickel ferrite, NiFe2O4, phase can be obtained by thermal treatment of the

precursors at temperature >800 ◦C for 120 min in the studied pH range, from 7

(neutral) to 12 (highly alkaline). In the temperature range of 500 ◦C≤T≤800 ◦C,

impure low crystalline NiFe2O4 phase is formed. The main impurities are

FeO(OH) and Fe2O3-H2O phases. Higher magnetization (32 emu g−1

) is obtained

for a precursor precipitated at pH 10 and thermally treated at 1200 ◦C for 120

min. Prepared nickel ferrite samples showed a good response toward CO

oxidation. It is concluded that the lower crystal size (8.5 nm) enhanced CO

adsorption and consequently its oxidation.

Arulmurugan et al (26)

Co–Zn substituted nanoferrites having stoichiometric

composition Co1-xZnxFe2O4 with x ranging from 0.1 to 0.5 were prepared by

chemical coprecipitation method. The precipitated particles were used for the

preparation of ferrofluid. Ferrofluids having Co0.5Zn0.5Fe2O4 particles could be

used for the energy conversion application utilizing the magnetically induced

convection for thermal dissipation. The final estimated cation contents, agreed

with the initial degree of substitution. The powder samples were characterized

by XRD, TEM, VSM and Mossbauer studies. The precipitated particles showed

single-phase fcc spinel structure for all compositions of zinc. The magnetic

parameters such as Ms, Hc, Mr, Tc and particle size were found to decrease with

the increase in zinc substitution. In the case of particles with higher zinc

concentration, both ferrimagnetic nanoparticles and particles exhibiting

superparamagnetic behavior were present. The fine particles were suitably

dispersed in heptane using oleic acid as the surfactant. Volatile nature of the


14

carrier chosen helped in altering the number concentration of the magnetic

particles in a ferrofluid.

Abo El Ata et al (27)

studied the AC electrical conductivity and initial

magnetic permeability were investigated for some Rare earth- substituted spinel

ferrites. These ferrites are of composition Li0.5-0.5xCoxFe2.4-0.5xR0.1O4 (where x=

0:0; 0.5, and 1; R = Y, Yb, Eu, Ho and Gd). They were prepared by standard

ceramic techniques. With respect to AC electrical conductivity, measurements

show dispersion with frequency at low temperatures. This dispersion obeys the

universal power law. The frequency exponent of the power law decreases with

both Co ion content and temperature. This indicates that the classical barrier

hopping mechanism is the predominant one in these samples. On the other hand,

the behavior of the initial magnetic permeability with temperature exhibits

multidomain structure only for the samples with x ¼ 0:0; and single domain

structure otherwise.

Ch. Venkateshwarlu (28)

investigated thermoelectric power studies of

cobalt substituted copper ferrites of various compositions were investigated

from room temperature to well beyond the Curie temperature by the differential

method. The Seebeck coefficient is negative for all the compositions showing

that these ferrites behave as n-type semiconductors. Plot of Seebeck coefficient

versus temperature show a maximum at Curie temperature. On the bases of

these results an explanation for the conduction mechanism in Cu–Co mixed

ferrites is suggested.

C. Caizer et al(29)

. investigated system consisted of Co ferrite

nanoparticles embedded in amorphous SiO2 particles, with ɛ = 1%, magnetic

volume fraction. The M–H curve (M is the magnetization and H is the external

magnetic field) of the particle system, recorded at room temperature using a

Documents

Study of the physical properties of Co-Ti substituted rare ... · prepared by standard ceramic technique of Co-Ti substituted rare earth ferrite ... The ionic radii on A and B sites