| 1

Ferrites belong to a special class of magnetic material consisting

of metal oxide and ferric oxide as their main compositions. The novel

magnetic, electric and dielectric properties possessed by them have

made ferrites more attractive to the current field of science and

technology. These important properties of ferrite finds application in

micro-electric devices, magnetic switches, sensors, microwave devices,

electromagnetic circuits, transformer core, antenna rods and in the field

of medicines [1-2]. These properties are largely dependent on chemical

composition, method of synthesis, synthesis conditions, grain size and

surface morphology [3-5].

Ferrites are still of interest as promising materials for many

applications. For these reasons engineers and scientists are keenly

interested in determining their characterization. Since ferrites behave as

low gap semiconductors and as insulators at low temperature, they have

been used in number of technological applications. These applications

include microwave devices, magnetic and magneto-optic recording, data

storage etc. [6,7].

Extensive research has focused on investigating the basic

structural, electrical, dielectric and magnetic properties of ferrites. The

properties of ferrite can be altered by substituting different cations at

available sites. The study of cation distribution in ferrite is of important

aspect in order to understand the magnetic as well as structural and

other properties. Many researchers have indicated that ferrites with

spinel structure are promising electric material [8]. The spinel ferrites

1.1 INTRODUCTION

| 2

have remarkable magnetic and electrical properties. Ferrites with spinel

structure are significant material in development of several technological

applications where materials with high density and low porosity are

necessary like other ceramic materials ferrites are also commonly

obtained in solid phase reaction from different oxides. In the recent

decade ferrites are prepared in nano-size or by several wet chemical

methods. The properties of ferrite material in bulk and nano-size form

are different from each other due to size effect. The wet chemical

methods include hydrothermal synthesis [9] co-precipitation method [10]

sol-gel method [11-13] plasma synthesis method [14] and micro-wave

synthesis method [15]. These wet chemical methods effectively affect the

crystal size and sintering temperature. It has been reported that the

physical properties like structural, electrical, dielectric, magnetic etc. of

the ferrite material are strongly influenced by radiation effects [16-18].

This work is directed towards the effect of gamma irradiation on

the physical properties of ferrite materials. The interaction of gamma

rays with spinel ferrite and secondary electrons produced by the photo-

Compton effects during this processes is discussed briefly in order to

study their effect these properties which may bring the ferrites

technologically more applicable.

Ferrites are ferrimagnetic materials having iron oxide as their

main component along with the metal oxides. On the basis of crystal

structure ferrites are mainly divided in to three groups namely spinel

ferrites, garnets and hexa-ferrites. On account of their crystal structure

they can accommodate a variety of cations at their interstitial sites

1.2 CLASSIFICATION OF FERRITE

| 3

bringing wide variation in the properties. The applications of spinel

ferrites, garnet and hexa-ferrite are different due to their crystal

structure. All these types of ferrites are equally important from the point

of view of their application and therefore they are widely studied by

many researchers. [19-20]

Table 1.1

Classification of Ferrite materials

Sr.

No Parameter Hexagonal Garnet Spinel

01 Structure Cubic Cubic Cubic

02 Molecular Formula M(Fe12O19) M3(Fe5O12) M(Fe2O4)

03 Space Group P63/mmc,

D6h Ia-3d 3Fd m

04 Interstitial Sites 12k,2a,4f2,

4f1, 2b a, c and d (A) & [B]

05 Examples CaFe12O19 Y3Fe5O12 CoFe2O4

06 Lattice Constant (Å) 5.83 12.37 8.38

07 Curie Temp. (K) 673 553 668

08 Saturation Magn. emu/gm 66 26 63

09 Electrical Resistivity, Ω-

cm 1×106 1×1014 1×108

1.2.1 Spinel ferrites:

Spinel ferrites are characterized by the formula MFe2O4 where M

stands for divalent metal ions like Cu, Ni, Mg, Mn, Co, Zn, Cd etc. M can

be replaced by other divalent metal ions. Fe3+ can be replaced by other

trivalent ions like Al, Cr, Ga, In etc. The crystal structure is cubic with

spinel type (MgAl2O4) and possesses two interstitial sites namely

| 4

tetrahedral (A) site and octahedral [B] site. The unit cell is made up of

eight units (cube) and may thus be written as M8Fe16O32. The structure

was first determined by Bragg and Nishikawa [21].

Fig.1.1 Spinel structure.

1.2.2 Classification of spinel ferrite

Spinel ferrites are classified into three types on the basis of the

distribution of cations in the two principal sites, tetrahedral site (A) and

octahedral site [B] [22], into three types.

Normal spinel ferrite

Inverse spinel ferrite

Random spinel ferrite

a) Normal spinel:

A ferrite is called normal spinel when the divalent metal ions

occupy the tetrahedral (A) sites while 2Fe3+ ions are at octahedral [B]

site. The best examples of normal spinel ferrites are zinc (ZnFe2O4) and

cadmium ferrites (CdFe2O4), in which the divalent metallic ions Zn2+ or

Cd2+ are at the (A) site, while Fe3+ ions are at [B] site. The cation

distribution can be represented as in general

(M)A [Fe2]B O4 ….1.1

| 5

b) Inverse spinel:

In inverse spinel ferrite, one trivalent ferric ion Fe3+ is at the

tetrahedral (A) site while the remaining trivalent ferric ions Fe3+ and the

divalent metallic ions M2+ are at the [B] site. Actually most of the simple

ferrites, e.g. Nickel ferrite, Cobalt ferrite are of the inverse spinel

structure [23]. The cation distribution in inverse spinel ferrite can be

written as

(Fe)A [MFe]B O4 ….1.2

c) Random spinel:

The divalent metal ions M2+ and trivalent Fe3+ ions are distributed

at both tetrahedral A site and octahedral [B] site then the ferrite is

termed as random spinel ferrite. The best known example of random

spinel ferrite is copper ferrite. The distribution of ions between two types

of sites is determined by a delicate balance of contributions, such as the

magnitude of ionic radii, their electronic configuration and the

electrostatic energy of the lattice [24-25]. In general, the cation

distribution in random spinel can be written as

(M1-xFex)A [MxFe2-x]B O4 ….1.3

1.2.3 Crystal structure of spinel ferrite

The spinel crystal structure is determined primarily by the oxygen

ions lattice. The radii of oxygen ions are several times larger than the

radii of metallic ions in the compound. Consequentially, the crystal

structure can be thought of as being made up of the closest possible

packing of layers of oxygen ions, with the metallic ions fit in at the

interstices.

| 6

Wyckoff [26] gives the spinel space group as :

cation 16c

,

,

,

;

cation 8f

,

,

;

with the translations, for a face-centered lattice, Packing of the ions

within the lattice is perfect when the oxygen parameter u =

1.2.4 Cubic garnets:

Cubic garnets are represented by the formula REFe5O12 where RE

is yttrium or rare earth ions like Dy, Gd, La, etc. The structure of garnet

is also cubic and possesses three interstitial sites namely dodecahedral

(c), octahedral (a) and tetrahedral (d) sites. The crystal structure is of a

cubic form with 160 atoms per unit cell and containing 8 molecules of

REFe5O12. The ions are arranged on a b.c.c. lattice with c and d- ions

lying on cube faces [27].

Figure1.2: Garnet structure.

| 7

The unit cell consists of eight of these sub units with 24 c- ions, 16 a-

ions and 24 d-ion. Each a ions is surrounded by six oxygen ions to form

a octahedral sites, each c-ion by eight oxygen ions forming a

dodecahedral and each d-ion by four oxygen ion to form a tetrahedral.

The rare earth garnets have the general formula 12d3

a2

c3 OFeFeM or

(3M3O3) c (2Fe3O3) a (3Fe2O3) d where M is a rare earth metal ion or an

yttrium ion (such as nonmagnetic yttrium or a magnetic rare earth) and

the superscripts c, a, d refer to dodecahedron, octahedron and

tetrahedron respectively.

1.2.5 Hexagonal ferrites:

Hexagonal ferrite was first identified by Went, Rathenau, Gorter &

Van Ostershout and Jonker, Wijn & Braun. Hexagonal ferrites are

denoted by the formula MeFe12O19 where Me = Ba, Sr, or Pb. The crystal

structure is hexagonal with the unit cell made up of two unit formulae.

Figure1.3: Hexagonal structure.

| 8

The lattice has three different sites occupied metal ions,

tetrahedral, octahedral and trigonal bi pyramid (surrounded by 6 oxygen

ions). The structure is related to the spinel structure in which the

oxygen lattice, being f.c.c., consist of a series of hexagonal layers of

oxygen lying perpendicular to the (111) direction and with layer arranged

ABC, ABC. The hexagonal ferrites are of M, W, Y, Z, X and U type [28].

The crystal and magnetic structure of the different types of hexagonal

ferrites are remarkably complex. Because the direction of magnetization

cannot be changed easily to another axis, hexagonal ferrites are referred

to as “hard” ferrites.

Among the three types of ferrites spinel ferrites finds a special

class from the point of view of their wide applications in many field and

academic point of view.

Ferrite materials have a wide range of applications. They are

magnetic ceramics usually composed of oxides of iron and metals.

Ferrites having semiconductor nature are the most important materials

because of their interesting electrical and magnetic properties. On the

basis of their application ferrites can be classified as soft ferrite and hard

ferrite.

Soft ferrites:

Soft ferrites are used for transformer cores, inductors, SMPS,

inductors, convertors, EMI filters, picture tube yokes etc. They are

extensively used in television, telecommunication, space research,

military devices and include variety of industrial applications [29-34].

They are mixed ferrite having a combination of two metals like Mn, Zn,

1.3 APPLICATIONS OF FERRITES

| 9

Mg, Cu and Ni. They are useful at high frequencies due to their low

losses, high resistivity, low values of remnant, flux density and low

values of coercive force. They have high permeability.

Hard ferrites:

Hard ferrites are used for permanent magnets. Barium ferrites are

the most important type of ceramic permanent magnets. They make

efficient transformer core with low eddy current loss at high microwave

frequency. They have high value of coercive force than Alnico alloys. They

have high resistance to demagnetization. Barium hard ferrite are used as

focusing magnets for TV tubes, small dc motors and compact torque

devices. The other hard ferrites are PbO 6Fe2O3 and SrO 6Fe2O3. Hard

ferrites are also used for magnetic latch and magnetic levitation purpose.

High frequency applications:

Ferrites are interesting high frequency material used as rotator,

phase shifter, circulator, radar, aircraft, satellite guidelines, space

communication systems etc. They are good magnetic shielding material.

so, radar absorbing paint containing ferrite materials have been

developed to render an aircraft or submarine invisible [35-36].

Data storage:

Ferrites are useful as computer memory devices. Magnetic

recording media, these ferrites possess rectangular hysteresis loop.

Microwave applications:

Ferrites and garnets are used as components of electronic filters,

microwave devices, magnetic switches and memory elements for

computers. For memory and switching devices ferrites are used in the

| 10

form of thin films. Ferrites are extensively used in fabrication of radio

frequency coil, rod antenna etc [37-39].

Magnetic Sensors:

Sensors made from ferrites having sharp and definite Curie

temperature are used for temperature control. Position and rotational angle

sensors (proximity switches) have also been designed using ferrites [41].

Humidity Sensitivity:

Ferrite having large surface area, high surface charge density and

with open pore formed on bulk surface is a strong reason behind their

use for humidity sensitivity [42-43].

Biomedical application

Hyperthermia cancer therapy, drug delivery, Radiotherapy, AC

magnetic field assisted cancer therapy are among some of the medical

applications of ferrite nano materials. The magnetic nanoparticles can be

injected in the patient’s body and translocate to the tumor cells. Then

energy for magnetic moment is provided by external magnetic field

applied. This causes a dissipation of energy and generates heat in the

tumors. The cancerous cells have high temperature sensitivity and so,

will be destroyed. Super paramagnetic nanoparticles do not have

remenance and thus the harm of thrombosis is avoided.

Magnitude of magnetization, coercively, magnetocrystallie, shape

anisotropy of ferrite nano material used plays an important role in this

therapy [44-46].

Metallurgical application

Ferrites are used in many metallurgy applications and material testing.

| 11

Table 1.2

Various applications of ferrite materials

Soft Ferrites

•Inductors

•Smps

•Transformer Cores

•Convertors

•Emi Filters

•Picture Tube Yokes

•Televission

•Communication

•Space Research

Hard Ferrites

•Parmanent Magnets

•Transformer Cores

•Tv Tubes

•Small Dc Motors

•Compact Torque Devices

•Magnetic Latch

•Magnetic Lavitation

High Frequency Application

•Rotators

•Phase Shifters

•Circulators

•Radar

•Aircraft

•Satellite Guidelines

•Space Communication

Systems

•Magnetic Shielding

Paints

Data Storage Devices

•Substrate For Buble

Memories

•Computer Memory Chips

•Magnetic Recording

Media

•Memory Cores

Microwave Applications

•Noise Absorbing

Cores

•Insulators

•Electronic Filter

•Magnetic Switches

•Radio Frequency Coil

•Antenna Rods

Magnetic Sensors

•Magnetic Sensor

•Humidity Sensitivity

•Material Testing

•Metullurgy Application

Other Applications

•Power Transformer

•Reactor Core

•Fly Block Transformer

Core

•Deflection Yoke Core

•Picture Tube Core

Biomedical Applications

•Hyperthermia Cancer

Therapy

•Drug Delivary

•Radio Therapy

•Cell Lebelling

| 12

Spinel ferrites are one of the most important classes of magnetic

materials exhibiting number of interesting applications which are useful

to mankind. In the spinel structure the magnetic ions are distributed

between two different sub-lattices, tetrahedral (A) and octahedral [B]

sites. The magnetic as well as electrical properties of ferrite vary with

occupancy of captions at tetrahedral (A) site and octahedral [B] sites,

nature of substituent cations besides the method of preparation and

preparation condition.

In the literature numbers of reports are available on the

structural electrical dielectric and magnetic properties of cobalt ferrite

substituted with divalent, trivalent and tetravalent ions [47-49].

It is reported in the literature that the properties of cobalt ferrite and

substituted cobalt ferrite are influenced by subjecting it to various kinds

of radiation viz. swift heavy ion, laser beam and the gamma radiations

[50-51]. The properties are changed due to defects produced in the

crystal structure.

N. Okasha et al. has enhanced the magnetization of Mg-Mn nano-

ferrite by gamma irradiation with Co-60 gamma source (A radioactive

isotope of cobalt with mass number 60 and exceptionally intense gamma

ray activity, used in radiotherapy metallurgy and material testing) [52].

M. A. Mousa and M. A. Ahmed have reported electrical conduction in

gamma irradiated and unirradiated Zinc Iron ferrite.

The gamma irradiation process causes a decrease in the electrical

conduction due to decrease in the Fe2+, Fe3+ ratios on octahedral site.

They have discussed the effect of gamma irradiation on the electrical

1.4 LITERATURE REVIEW

| 13

conductivity, charge carrier and conduction mechanism in Co-Zn spinel

ferrites [53]. E. Ateia shows the gamma irradiation dependence of

electrical conductivity and dielectric constant of ferrite materials. Co Zn

Ce ferrite tablets were exposed to Co60 γ-rays at different doses (100

krad, 500 krad and 5 Mrad) [54]. Jitendra Pal Singh et al. have reported

magnetic study of nanostructured Zinc ferrite. In this work they

observed that the particle size of the system remains almost same after

irradiation. The magnetization of the sample decreases after irradiation

at 310 K. Super paramagnetic domains are observed for both irradiated

and unirradiated Zinc ferrite, the blocking temperature decreases from

276-63 K after irradiation [55].

Some Co-Zn doped spinel ferrites irradiated with Co60 gamma

radiation of dose 106 rad/h were studied for crystal structure, lattice

parameter ad diffusion coefficient by Dalal Mohammed Hemeda [56]. M.

Mane et al. shown that the structural cation distribution and magnetic

properties of lithium ferrite were modified after energetic 60Co gamma

radiation exposure with different doses (1, 2 and 3 Mrad) with dose rate

of 140 rad/min [57].

O. M. Hameda and M. El-Saadawy synthesis Co-Zn spinel ferrite

by ceramic technique and studied the effect of dose rate 1 Mrad/hr of

energetic gamma radiation on the structural and other properties. The

diffusion coefficient of oxygen vacancies was measured from D.C.

conductivity studies and found that diffusion coefficient increase after

gamma irradiation for all zinc concentration. The lattice constant of the

system increases after irradiation [58]. N. Z. Darwish et al. thrown light

on structural and dielectric properties and try to analyze the mechanism

| 14

of 60Co gamma radiation interaction (Total dose used 106 rad.) with of

Co-Zn ferrite lattice [59]. M. A. Ahmed and Samiha T. Bishay reported

improvement in conductivity of Li-Co-Yb ferrite with gamma dose of 1

and 3 Mrad [60]. A. Tawfik et al. reported effect of laser irradiation on

the structural and electromechanical properties of cobalt zinc ferrite.

According to them the electrical resistivity decreases after irradiation the

X-ray diffraction pattern of irradiated samples by laser show a distorted

cubic structure [61].

In the literature, the structural electrical and magnetic properties

of spinel ferrite irradiated by swift heavy ion are also reported M. C.

Chhantbar et al. reported the structural and magnetic properties of Ti4+

Li-Al and Li-Cr ferrtes irradiated by 50 Mev Lic-Me+ ions [62]. Ravi

Kumar et.al has worked on effect of swift heavy ion irradiation on the

various properties of different spinel ferrite systems. Their study reviled

that the properties of spinel ferrites are greatly influenced by swift heavy

ions irradiations [63].

Thus, it is revealed from the literature survey that the structural,

electrical and magnetic properties of spinel ferrites are influenced by

various kinds of irradiation. More change is observed in electrical and

magnetic properties. Further the modification in the properties of spinel

ferrite depends upon dose rate of gamma radiation.In the family of spinel

ferrite, cobalt ferrite is of unique spinel ferrite with high electrical

resistivity, high saturation magnetization, high Currie temperature, low

eddy current and dielectric losses, large magneton isotropy, chemically

stable and magnetically hard. The substitution of zinc in spinel ferrites

can give rise to many interesting properties. It is now established fact

| 15

that the properties of spinel ferrite are greatly influenced when the

particle size is reduced from micrometer to nanometer range. Most of the

studies reported in the literature on cobalt zinc ferrite are related to bulk

material. Very few reports are available in the literature on the effect of

gamma irradiation on the properties of Nano crystalline cobalt zinc

ferrite.

The aim of the present work is to synthesis zinc substituted

cobalt ferrite with generic formula Co1-xZnxFe2O4 (with x = 0.0, 0.2, 0.4,

0.6, 0.8 and 1.0) by sol-gel autocombustion method with a view to obtain

nano-size particles. Cobalt ferrite, (CoFe2O4) is a well-known hard

magnetic material, which has been studied in detail due to its high

coercivity (5400 Oe) and moderate saturation magnetization (about 80

e.m.u. gm-1) as well as a remarkable chemical stability and a mechanical

hardness [37]. Zinc ferrite (Zn) belongs to the category of normal

spinels.

The structural and magnetic properties of zinc ferrites have been

the subject of study by various researchers over the last two decades

[38]. Co-Zn ferrite are quite important in the field of microwave industry,

their usage is influenced by their physical and chemical properties

which is in turn influenced by several factors such as method and

conditions of preparations as well as the amount and type of additives

[35]. To our knowledge, very few reports are available on gamma

irradiation studies of zinc substituted cobalt ferrite synthesized by sol-

gel auto-combustion technique. It was decided to investigate thoroughly

the structural, microscopic, electrical, magnetic and dielectric properties

1.5 AIM OF PRESENT WORK

| 16

of cobalt zinc polycrystalline nano ferrites before and after gamma

irradiation, by means of X-ray diffraction, Infrared spectroscopy,

Scanning Electron microscopy, D. C. electrical resistivity, pulse field

hysteresis loop technique etc. It is planned to investigate these physical

properties of Co-Zn spinel ferrite before and after gamma irradiation.

For the present study Co60 used as a source of energetic gamma

radiation. Different gamma doses were studied for irradiation process.

Total dose of 5 Mrad selected for gamma exposure. In the present study

the changes in different physical properties of ferrite materials were

aimed to compare with the selected dose of γ- rad. It was aimed to make

high performance ferrite materials with improved dielectric properties,

electrical resistivity, low eddy current and porosity. Co-Zn ferrites nano

particle were proposed to prepare by sol-gel autocombustion method as

more efficient and result oriented method among all wet chemical

methods. The scope of the research work is around the technical

importance of magnetically hard Co-Zn ferrite material.

The present investigation is differing from the previous works so

as to understand the role of two different γ-radiation doses over the

physical properties of Zn substituted Co ferrite material. The good

experimental efforts were taken behind the aimed approach which leads

to the desirable output. It may be interesting to comment on structural,

morphological, magnetic and electrical properties of gamma irradiated

bulk and nano-crystalline Co1-xZnxFe2O4 ferrite system. This will open a

new era for using gamma irradiation in optimizing the physical

properties of the investigated samples to be more applicable.

| 17

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