Synthesis of Synthesis of magnetic materials magnetic materials

with ferrite as with ferrite as potential applicantpotential applicant

Dr. K. G. RewatkarDr. K. G. Rewatkar Department of physics,Department of physics,

Dr. Ambedkar College, Dr. Ambedkar College,

NagpurNagpur

Basic Magnetic Quantities

Magnetic Induction or

Magnetic Flux Density B

BvF q

Units: N C-1 m-1 s = Tesla (T) = Wb m-2

2006 : UNESCO Nikola Tesla Year

150th birth Anniversary of Nikola Tesla

Ampere’s law in free space

id 0. lB

i

B

0= permeability of free space

= 4 10-7 T m A-1

= 4 10-7 H m-1

Magnetic dipole moment m

i

Area=A

m=iA

Units: A m2

V

mM

Magnetization M of a solid

A solid may have internal magnetic dipole moments due to electrons

Magnetic dipole moment per unit volume of a solid is called magnetization

Units: A m2/m3 = A m-1

Ampere’s law in a solid

id 0. lB

i

B0

lMlB did .. 00

id

l

MB.

0

0

MHB 00

id lH.

H: magnetic field intensity Units: A m-1

In free space

HB 0

Inside a solid

MHB 00

HB

1

3

2

= permeability of solid, H m-1

relative permeability of solid, dimensionless 0

r

HM : magnetic susceptibility of the solid

Type of magnetic solid

dimensionless

diamagnetic -10-5

superconductor -1

paramagnetic +10-3

ferromagnetic

(universal)

+103-105

4

Origin of permanent magnetic moments in solids:

1. orbital magnetic moment of electrons

2. spin magnetic moment of electrons

3. spin magnetic moment of nucleus

We will consider only spin magnetic moment of electrons

Bohr magneton B

The magnetic moment due to spin of a single electron is called the Bohr magneton B

B= 9.273 x 10-24 A m2

Net moment of two electrons of opposite spins = 0

Unpaired electrons give rise to Paramagnetism in alkali metals

Na 3s1

Net magnetic moment

1 B

Fe 3d64s2 4 B

atom crystal

2.2 B

Co 3d74s2 3 B 1.7 B

Ni 3d84s2 2 B 0.6 B

Example :

The saturation magnetization of bcc Fe is 1750 kA m-1. Determine the magnetic moment per Fe atom in the crystal.

a = 2.87 Å V = a3 = 2.873x10-30

Magnetic moment per atom

=1750x1000x2.873x10-30

=2.068x10-23 A m2

=2.2 B

Ferromagnetic, ferrimagnetic and antiferromagnetic materials

Due to quantum mechanical interaction the magnetic moment of neighbouring atoms are aligned parallel or antiparallel to each other.

Ferro-magnetic

Anti-ferromagnetic

Ferri-magnetic

ferromagnetic Fe, Co, Ni, Gd

Element

orbitald

atom

d

d

3

Ti Cr Mn Fe Co Ni

1.12 1.18 1.47 1.63 1.82 1.98

Eexchange interaction= Eunmagnetized-Emagnetized

1.5-2.0

Heusler Alloys: Cu2MnSn, Cu2MnAl

Ferromagnetic alloys made of non-ferromagnetic elements

Thermal energy can randomize the spin

Ferromagnetic ParamagneticTcurie

heat

Fe 1043 K Co 1400 K

Ni 631 K Gd 298 K

Cu2MnAl 710 K

Ferrimagnetic materials

24

32

2 OFeMFerrites

M2+: Fe2+, Zn2+, Ni2+,

Mg2+, Co2+, Ba2+, Mn2+

Crystal structure: Inverse spinel

24

32

2 OFeMFerrites

O2+ FCC packing

Net moment due to M2+ ions only.

4 O2+

8 THV

4 OHV

Antiferromagnetic coupling

Fe3+

Fe3+ M2+

THV = Tetrahedral

OHV = Octahedral

If Fe is ferromagnetic with atomic magnetic moments perfectly aligned due to positive exchange interaction then why do we have Fe which is not a magnet?

Answer by Pierre Ernest Weiss (1907)

Existence of domains known as Weiss domains

Domain walls are regions of high energy (0.002 Jm-2) due to moment misalignment.

Randomly aligned domains

1. decrease the manetostatic energy in the field outside the magnet

2. increase the domain wall energy inside the magnet

A magnet will attain a domain structure which minimizes the overall energy

MHB 00

B never saturates

M saturates

The value of B at the saturation of M is called the saturation induction (~ 1 T)

Two ways for aligning of magnetic domains:

1.Growth of favorably oriented domains (initially)

2.Rotation of domains (finally)

Initial permeability

Saturation induction

The hysteresis Loop

Br residual induction

Hc coercive field

Area = hysteresis loss

Soft magnetic materials

High initial permeability

Low hysteresis loss

Low eddy current losses

For application requiring high frequency reversal of direction of magnetization

Eg. Tape head

Easily moving domain walls

Low impurity, low non magnetic inclusions

low dislocation densitylow second phase precipitate

Soft magnetic materials

For low hysteresis loss ( frequency)

For low eddy current loss ( frequency2)

Material: high resistivity

Design: Lamination

Choose: Pure, single phase, well-annealed material of high resistivity

Hard magnetic materialsFor permanent magnets

Motors, headphones

High Br, high Hc

Br Hc = energy product

Martensitic high carbon steels (Br Hc=3.58 kJm3)

Alnico alloys: directionally solidified and annealed in a magnetic field (Br Hc=5.85 kJm3)

Mechanically hard c Magnetically hard

Large M phase as elongated particle in low M matrix

Elongated Single Domain (ESD) magnets

Long particles, thickness < domain wall thickness

Each particle a single domain

No domain growth possible only rotation

Ferrite: BaFe12O19 (Br Hc=48-144 kJm3)

Co-Rare Earths (Sm, Pr) (Br Hc=200 kJm3)

Nd2 Fe14 B (Br Hc=400 kJm3)

The term “ferrite’ means different to different scientists.

To metallurgists, ferrite means pure iron. To geologists, ferrites are a group of minerals based on iron oxide.

To an electrical engineer, ferrites are a group of materials based on iron oxide, but one that have particular useful properties: magnetic and dielectric.

Magnetite or Lodestone is a naturally occurring iron oxide that is considered a ferrite by both geologists and engineers. Over 2,000 years ago, the Greeks recognized the strange properties of Lodestone and almost 1000 years ago the Chinese used it to invent the magnetic compass. Dielectric properties mean that even though electromagnetic waves can pass through ferrites, they do not readily conduct electricity. This gives them an advantage over iron, nickel and other transition metals that have magnetic properties (“ferromagnetic”) in many applications because these metals also conduct electricity.

Magnetite, i.e., Fe+2Fe+3O-4 (FeO,Fe2O3) is a naturally occurring ferrite. The first artificial ferrite was actually made in 1909 by Hilpert.

Scientific research on ferrite begun in the mid - nineteenth century. Two Japanese scientists Kato Yogoro and Takei Takeshi (1932) took the initiative in conducting serious research oriented to industrial applications. Their series of research results on Cu ferrite and Co ferrite in the year beginning 1932 become the nucleus and motive force which, as is well known led to the world’s first application of ferrite on a commercial basis.

ORIGIN OF MAGNETISM

Basically every materials is magnetic in nature, as it possess charged particles which are in continuous motion. Magnetism is present mainly due to the motion of electrons.

mc

eh

4

B = 9.27 x 10-21 erg/oersted

The magnetic interaction, which arises because of the relative orientations of the orbital and spin moments of various electrons are as follows:

• The coupling of orbital motion of electrons and spin momenta leads to Coulomb

interaction.• Spin – orbit interactions, which magnetically

couple the orbital motion of each electron to its own spin.

• Interactions produced because of electric field of neighbouring ions of the crystalline lattice.

CLASSIFICATION OF MAGNETIC MATERIALS

• Non – Cooperative phenomenaWhere there is no collective magnetic interaction of atomic magnetic moments with each other and are not magnetically ordered.

ex: (i) Diamagnetic materials (ii) Paramagnetic materials

• Cooperative phenomenaWhere the magnetic dipoles interact with each other introduces three types of behaviour, ex: (i) Ferromagnetism (ii) Antiferromagnetism (iii) Ferrimagnetism.

(a)Paramagnetic state(b)Ferromagnetism(c) Neel type

antiferromagnetism (d) Neel type

ferrimagnetism(e) Yafet – Kittel type ferrimagnetism(f) Helical spiral structures(e) Canted spin weak ferromagnets(h) Canted spin compensated antiferromagnets

(a) (b)

(e)

(c)

(d)

(a) Diamagnetism (b) Paramagnetism(c) Ferromagnetism(d) Antiferromagnetism (e) Ferrimagnetism

(a) (b)

(c) (a)Diamagnetism(b)Paramagnetism (c)Antiferromagnetis

m

Hysteresis loop

GENERAL PROPERTIES OF FERRITES

• Ferrites are generally black or grey in appearance. Most ferrites are opaque. This can be attributed to the approximately equal energies of the 3d and 4s states. This is also because the absorption in case of ferrites crystal structure occurs only in visible

range thus making them black by Waldron (1961). .

• Ferrites have high dielectric constant. Its values are generally of the order of thousands at lower frequencies, falling to about ten to twenty at microwave frequencies. This is due to the close-packed structure( hcp ) of oxygen ions .

GENERAL PROPERTIES OF FERRITES

• Ferrites are very hard and brittle and have high melting point. Again this is due to the fact

that oxygen ions have a close-packed spatial formation, thus making the ionic bonds very strong.

• The ferrites melting points are difficult to measure because they lose oxygen at high temperatures.

• Ferrites are non-conductors of electricity but behave as semiconductors under the

influence of an applied electric field.

Ferrites are best known for their

magnetic properties. • Magnetic Anisotropy: - Most of the ferrites have an ability to get completely magnetized along a preferred axis on the application of magnetic field.

• Hysteresis and Permeability: - Ferrites have either thin hysteresis loop or square loops. The ferrites with this loop come under the class of soft ferrites and finds applications in devices like

transformers and inductors. The other with square loop are classified as hard ferrites which find applications in memory devices

CLASSIFICATION OF FERRITES

Ferrites are usually classified as soft ferrites , moderate and hard ferrites. The distinguishing characteristic of the first group is high permeability. Its flux – multiplying power made it suitable for their job in machines and devices.

The terms “SOFT” has nothing to do with their physical properties but refers to their magnetic characteristics. Soft ferrite dose not retain significant magnetization whereas hard ferrite magnetization is considered permanent. Soft ferrite is the general term to a class of ceramic and electromagnetic materials.

Magnetically hard materials, on the other hand are made into permanent magnets having high coercivity as it once magnetized may be able to resist the demagnetizing action of stray fields including its own.

Spinels (soft)M+2Fe2

+3O4

Cubic with 8 formula unitTwo sites tetrahedral (A) & octahedral (B) site.

Normal M-occupy A siteFe occuoy B site

Inverse½ of Fe occupy B site& ½ of Fe occupy A siteM occupy B site

RandomM & Fe occupy A & B site

Garandnet (moderate)Y3

+3Fe5+3O12

BCC in cubic with 8 formula unit Having three sites Tetrahedral Octahedral Fe+3 ions occupy tetrahedral & octahedral sites in 2:3 ratio, while Y+3 ions occupy dodecahedral sites

Hexaferrites (hard)M+2Fe12

+3O19

Hexageonal with 2 formula unit

Magnetic oxides Ferrites

46

Spinel structure A B2 O4

oxygen

B atoms in octa

A atoms in tetra

hedral positions

only front half of the cube is shown

each B atom has 6 oxygen n.n. each having just 1 A atom n.n.

B – O – A paths: 6 starting from B

each A atom has 4 oxygen n.n. each having 3 B atoms n.n. A – O – B paths:

12 starting from A

O2-4Co2+Fe3+Fe3+

tetra-

octa-hedral

positions

f.c.c. “frame”

with magnetic moments

5μB 3μB 5μB

O2-4Fe3+ Fe3+Co2+

tetra-

octa-hedral

positions

f.c.c. “frame”

with magnetic moments

3μB 5μB 5μB

inverse normal

Co2+1-i

Fe3+i

mixed with i = degree of inversion

Co2+i

Fe3+2-i

M = MB-MA =[3i+5(2-i)]-(5i+3-3i) =

=[10-2i] – (3+2i) = {7 – 4i} [μB]

Co ferrite – distribution of cations over A and B sites

Garnet FerritesThese are the ferrites that can accommodate large trivalent rare earth ions with large magnetic moments. Garnet ferrites have the structure of the silicate mineral garnet. Magnetic garnets crystallize in the dodecahedral or 12-sided structure related to the mineral garnet. The general formula is 3Me2O3.5Fe2O3 or Me3Fe5O12. It is to be noted that in this case all the metal ions are trivalent in contrast to the other two classes. In the important magnetic garnets, Me is usually Yttrium (Y) or one of the rare earth ions.

The general formula of the garnets can be represented schematically by {C3}[A2](D3)O12 where the cations are subdivided into three main sites with different coordinates. The cation C has dodecahedral, A octahedral and D tetrahedral coordination.

Naturally occurring magnetite is a weak ‘hard’ ferrite. Hard ferrites possess magnetism, which is essentially permanent. Man made hard ferrites with superior properties were developed but producing an analogous ‘soft’ magnetic material in the laboratory proved elusive.

In the case of hard ferrites, a strong magnetization remains after a magnetizing field has been removed and residual magnetization is stable even if certain strength of demagnetizing field is applied.

The best known compounds in this class are,

BaFe12O19, SrFe12O19, CaFe12O19 ,

PbFe12O19.

Symbol Crystallographic building up per unit cell

Number of molecules per unit cell

Chemical Formula Composition ( mol % )

MeO BaO Fe2O3

STB

MeO.Fe2O3

MeO.2Fe2O3

Bao.Fe2O3

MeFe2O4

BaFe4O7

BaFe2O4

50--

-33.33

50

5066.67

50

MWYZXU

RSR*S*RSSR*S*S*

3 ( ST )RSTSR*S*T*S*3( RSR*S*S* )RSR*S*T*S*

2M2MeW3MeY2MeZ3MeXMeU

BaO.6Fe2O3

2MeO.BaO.8Fe2O3

2MeO.2BaO.6Fe2O3

2MeO.3BaO.12Fe2O3

2MeO.2BaO.14Fe2O3

2MeO.4BaO.18Fe2O3

BaFe12O19

Me2BaFe16O27

Me2Ba2Fe12O22

Me2Ba2Fe24O41

Me2Ba2Fe28O48

Me2BaO4Fe36O60

-18.18

2011.7611.118.33

14.299.0920

17.6511.1116.67

85.7172.71

6070.5977.7875.00

*180 degree rotational symmetry around the hexagonal c-axis

Chemical composition of hexagonal compounds in BaO-MeO-Fe2O3 systems

M and Other related hexagonal ferrites

Chemical

Composition

Symbol* Structural Units

(Blocks)*

No. of Oxygen

Layers

Lattice

Parameter (c)

(Å)

BaFe12O19M RSR’S’ 2 x 5 = 10 23.19

Ba2Me2Fe12O22Y (TS)3

3 x 6 = 18 43.6

BaMe2Fe16O27W RS2R’S2

’ 2 x 7 = 14 32.8

Ba3Me2Fe24O41Z RSTSR’S’T’S’ 2 x 11 = 22 52.3

Ba2Me2Fe28O46X (RS2R’S2

’)33 x 12 = 36 84.1

Ba4Me2Fe36O60U (RSR’S’TS’)3

3 x 16 = 48 113

Various types of Hexagonal Ferrites

* The blocks with prime signs are related to the unprimed blocks by a 180o rotation about the c-axis.

Fe2O3

100

80

60

40

20

20 0

0

Y

Z W

BaFe2O4

M

20

40

60

80

100

0

BaO 100 80 60 40MeO

SX

M = BaFe12O19

W = BaMe2Fe16O27

Z = Ba3Me2Fe24O41

Y = Ba2Me2Fe12O22

S = Ba2Me2Fe28O46

The composition diagram of hexagonal ferrites

The symbol Me represent a divalent ion or a combination of divalent ions.

Perspective illustration of unit cell

of PbFe12O19

The sequence of layer in BaFe12O19

Coordination number Number of Wyckof’s Direction of magnetic Remarks

Positions notation moment per mole

6 12 k ↑ ↑ ↑ ↑ ↑ ↑ I (a)

(Octahedral site) 4 f2 ↓ ↓ III (d)

2 a ↑ V (b)

4 4 f1 ↓ ↓ II (c )

(Tetrahedral site)

5 2 b ↑ IV (e)

(Trigonal bipyramidal site)

Coordination number and direction of magnetic moment of Fe3+ ions in the unit cell of the magnetoplumbite type crystal.

Three types of locations in M structure

Exchange interaction scheme in the unit cell of M structure

(110) plane of the hexagonal structure of BaFe12O19. The strong lines indicate the most important exchange interactions between the five iron sublattices.

Formula a (Å) c (Å) Ref.

BaAl12O19 5.577 22.67 Adelskold (1938)

5.66 22.285 Bertaut et al. (1959)

SrAl12O19 5.557 21.945 Adelskold (1938)

CaAl12O19 5.566 22.010 Wisnyi (1967)

Ca(AlFe)12O19 5.792±0.004 22.56±0.04 MacChesney et al.(1971)

BaGa12O19 5.818 23.00 Bertaut et al. (1959)

5.850±0.004 23.77±0.02 Verstegen (1973)

SrGa12O19 5.796±0.004 23.77±0.02 Verstegen (1973)

LaMgGa11O19 5.799±0.003 22.71±0.01 Verstegen (1973)

BaCr8Fe4O19 5.844 22.82 Bertaut et al. (1959)

SrCr6Fe6O19 5.844 22.77 Bertaut et al. (1959)

CaFe11Ir0.5Co0.5O19 5.6952 22.8135 B. Sugg et al (1995)

CaFe10IrCoO19 5.8239 22.9256 B. Sugg et al (1995)

CaFe12O19 5.877 22.910 B.T. Borkar (1987)

CaLaFe11O19 5.880 23.082 N. Ichinose et al (1963)

CaFe10.8Ir0.6Co0.6O19 5.6392 22.8318 N.Y. Lange et al (2001)

Known compounds of substituted M-type compounds with Al, Ga, Cr, La etc.

Applications of materials

Permanent magnet Magnetic Recording Computer Microwave Radio and Television Telecommunication Miscellaneous uses

Motors Erase heads

Loud Speakers Magnetos

Rubber Magnet

Audio Tapes Magnetic diskette

Computer Tapes

Video Tapes Magnetic Cards

Pulse Transformer Cores

Memory

Cores

Substrates for

Bubble Memories

Reactor Cores

Power Transformers

Ferrite Microwave

Absorber

Rubber Ferrites

Noise Absorber Core

Isolators Circulator

Antenna Cores Type Tittles

Delay Line Cores

Fly back Transformer Cores

Rotary

Transformer Cores

Deflection

Yoke Cores

Low Accommodation

Cores

Low Temperature Coefficient Cores

Low Loss Cores High Stability Cores

Magnetic Recording Heads

IFT Cores

Impedar Cores

Ferrite Powder For Copying machine

Electrolytic Electrodes

Electromagnetic Cores

Magnetostrictive

Vibrators

Aplication of Magnetic Aplication of Magnetic CeramicsCeramics

Entertainment electronic (Radio, TV)ComputerMicrowave applications (Radar,

communication, heating)Recording TapePermanent motor

Aplication of Magnetic Ceramic Aplication of Magnetic Ceramic ferrites.ferrites.

Spinel (cubic ferrites): Soft magnets

Garnet (rare earth ferrites): Microwave devices

Magnetoplumbite (hexagonal ferrites): Hard magnets

Aplication ofAplication of Soft Soft MagneticsMagneticsIn the soft magnetic materials, only a

small field is necessary to cause demagnetization and very small energy losses occur per cycle of hysteresis loop.

This is important for applications such as transformers used in touch tone telephones or inductors or magnetic memory cores.

During used a soft ferrites has its magnetic domains rapidly and easily realigned by the changing magnetic field.

Aplication of Aplication of Hard Hard MagneticsMagnetics

A hard (or permanent) ceramic magnet achieves its magnetization during manufacture.

The magnetic domains are “frozen in” by poling in an applied magnetic field as the material is cooled through its Tc.

The materials are magnetically very hard and will retain in service the residual flux density, that remains after the strong magnetizing field has been removed.

Hard ferrites are used in loudspeakers, motors.

Aplication of FerritesAplication of FerritesThe cubic spinels, also called ferrospinels,

are used as soft magnetic materials because of their very low coercive force of 4x10-5 weber/m2 and high saturation magnetization 0.3-0.4 weber/m2.(1 weber = 1 volt-second = 108 Maxwells)

Flux density (induction): 1 Tesla = 104 Gauss = 1 weber/m2. (1 Gauss = 1 Maxwell/cm2).

Hexagonal ferrites are hard magnetic materials with coercive force of 0.2 – 0.4 weber/m2 and large resistance to demagnetization, 2 – 3 J/m3.

Aplication of GarnetsAplication of Garnets

Garnets are especially suited for high frequency microwave applications due to the ability to tailor properties such as magnetization, line width, g-factor, Tc, and temperature stability.

The most common garnet ferrites are based upon 3Y2O3 : 5Fe2O3 or Y3Fe5O12 or YIG.

Tape RecordingTape Recording Before passing over the record

head, a tape passes over the erase head which applies a high amplitude, high frequency magnetic field to the tape to erase any previously recorded signal and to thoroughly randomize the magnetization of the magnetic emulsion.

The gap in the erase head is wider than those in the record head; the tape stays in the field of the head longer to thoroughly erase any previously recorded signal.

Tape RecordingTape Recording High fidelity tape recording requires a high

frequency biasing signal to be applied to the tape head along with the signal to "stir" the magnetization of the tape .

This is because magnetic tapes are very sensitive to their previous magnetic history, a property called hysteresis.

A magnetic "image" of a sound signal can be stored on tape in the form of magnetized iron oxide or chromium dioxide granules in a magnetic emulsion.

The tiny granules are fixed on a polyester film base, but the direction and extent of their magnetization can be changed to record an input signal from a tape head.

ElectromagnetElectromagnet Electromagnets are usually in the form

of iron core solenoids. The ferromagnetic property of the iron

core causes the internal magnetic domains of the iron to line up with the smaller driving magnetic field driving produced by the current in the solenoid.

The solenoid field relationship is

and k is the relative permeability of the iron, shows the magnifying effect of the iron core.

TransformerTransformer A transformer makes use of Faraday’s law

and the ferromagnetic properties of an iron core to efficiently raise or lower AC voltages.

It of course cannot increase power so that if the voltage is raised, the current is proportionally lowered and vice versa.

Transformer

Applications of GMRApplications of GMR The largest technological application of GMR is

in the data storage industry. IBM were first to market with hard disks based

on GMR technology although today all disk drives make use of this technology.

On-chip GMR sensors are available commercially from Non-Volatile Electronics.

It is expected that the GMR effect will allow disk drive manufacturers to continue increasing density at least until disk capacity reaches 10 Gb per square inch.

At this density, 120 billion bits could be stored on a typical 3.5-inch disk drive, or the equivalent of about a thousand 30-volume encyclopedias.

Applications of GMRApplications of GMRGMR also may spur the replacement of RAM

in computers with magnetic RAM (MRAM). Using GMR, it may be possible to make thin-

film MRAM that would be just as fast, dense, and inexpensive.

It would have the additional advantages of being nonvolatile and radiation-resistant.

Data would not be lost if the power failed unexpectedly, and the device would continue to function in the presence of ionizing radiation, making it useful for space and defense applications.

Other applications are as diverse as solid-state compasses, automotive sensors, non-volatile magnetic memory and the detection of landmines.

Applications of GMRApplications of GMR

Reading and writing with a magnetoresistive probe.

C B Craus, T Onoue, K Ramstock,W G M A Geerts, M H Siekman, L Abelmann and J C Lodder, J. Phys. D: Appl. Phys. 38 (2005) 363–370

The preparation techniques reported for ferrites are-

Solid state method Co-precipitation Aerosol pyrolysis Hydrothermal synthesis Glass crystallization Microemulsion Dry milling method sol gel combustion route

Many plus of sol gel combustion route-

*energy efficient*short reaction rate*ultra fine powder of nano particles* facile operation* low anneal or calcine temperature*better particle size distribution*excellent chemical homogeneity *more probability of formation of single

domain structure

A series of samples were prepared of chemical formula Ca/Sr/BaFe12-xMxO19

A yellow–green-brown transparent aqueous solution of metal nitrates or chlorates, nitric acid and fuel as citric acid, urea and ethylene glycol was prepared.

It is important to note the mole ratio of citric acid to metals ions in solution.

The solution was heated under constant stirring at a temperature of about 100–150 oC in a Pyrex beaker, produced brown gel.

Experimental details ….Experimental details ….

PREPARATION OF SAMPLE BY SOL GEL ROUTE ….

PREPARATION OF SAMPLE BY SOL GEL ROUTE ….

PREPARATION OF SAMPLE BY SOL GEL ROUTE ….

The resulting brown/black were ground in an agate mortar, put into alumina crucibles, and then calcined at 150 oC for 1 h.

The powders and 10% polyvinyl alcohol solution (5–6 drops) had been mixed before they were pressed into pellets of 10 mm in diameter and about 5 mm in thickness.

The pellets of each composition which were then sintered at 800 oC for 4 h in air.

• Crystallographic structures were examined by powder X- ray diffraction (XRD). Morphology and grain size can be

determined with SEM and TEM.

• Hysteresis measurements/ Magnetic studies can be carried out on magnetic hysteresis recorder .

• Room temperature Mossbauer spectra were recorded using a constant acceleration spectrometer. (γ-ray source was 50mCi

57Co in Rh matrix)

• Morphology and grain size were taken with Scanning electron microscope. SEM and TEM studies reveals the nano-scale

crystalline structure of the compounds under study.

Experimental details ….Experimental details ….

XRD pattern of CaFeXRD pattern of CaFe12-x12-xCrCrxxOO1919

Variation of lattice (a and

c) parameters with Cr content CaFe12-

xCrxO19 with x = 0.0 - 0.8.

Formula a (Å) c (Å) Ref.

BaAl12O19 5.577 22.67 Adelskold (1938)

5.66 22.285 Bertaut et al. (1959)

SrAl12O19 5.557 21.945 Adelskold (1938)

CaAl12O19 5.566 22.010 Wisnyi (1967)

Ca(AlFe)12O19 5.792±0.004 22.56±0.04 MacChesney et al.(1971)

BaGa12O19 5.818 23.00 Bertaut et al. (1959)

5.850±0.004 23.77±0.02 Verstegen (1973)

SrGa12O19 5.796±0.004 23.77±0.02 Verstegen (1973)

LaMgGa11O19 5.799±0.003 22.71±0.01 Verstegen (1973)

BaCr8Fe4O19 5.844 22.82 Bertaut et al. (1959)

SrCr6Fe6O19 5.844 22.77 Bertaut et al. (1959)

CaFe11Ir0.5Co0.5O19 5.6952 22.8135 B. Sugg et al (1995)

CaFe10IrCoO19 5.8239 22.9256 B. Sugg et al (1995)

CaFe12O19 5.877 22.910 B.T. Borkar (1987)

CaLaFe11O19 5.880 23.082 N. Ichinose et al (1963)

CaFe10.8Ir0.6Co0.6O19 5.6392 22.8318 N.Y. Lange et al (2001)

Lattice parameter of some substituted M-type compounds with Al, Ga, Cr, La etc.

Effect of annealing temperature on the particle size ….

(a) (b)

(c) (d)

SEM of CaFe12-xCrxO19 for (a) = 0, (b) = 0.2, (c) = 0.4, (d) = 0.6

100 nm

Influence of heat treatment on the magnetic properties(Hc, Ms) of Sr(ZnTi)0.5Fe11.2O19

Magnetic properties of Sr(ZnIr)xFe12-xO19 vs. ‘a’ substitution content x

Effect of the pH on the phase formation, crystalline size and magnetic properties of strontium hexaferrite powders for Fe+3/Sr+2 ratio 10 and annealed at 1ooo0C for 2h.

Effect of Fe+3/Sr+2 mole ratio on M-H hysteresis loop of synthesized SrFe12O19 powders obtained annealed at 10000C for time 2h through co-precipitation route at pH 10 .

Coercivity of CaFe12-xCrxO19 pellets with x= 0 – 0.8

Saturation magnetizations of the CaFe12-xCrxO19 pellets with x= 0 – 0.8

Room temperature hysteresis of CaFe12-

xCrxO19

Fitted room temperature MÖssbauer spectrum of CaFe11.6Cr0.4O19

Hyperfine fields at each crystallographic site of CaFe12-xCrxO19 ceramics with x= 0 – 0.8

Relative areas on each crystallographic site of Relative areas on each crystallographic site of CaFe12-xCrxO19 ceramics ceramics with x= 0 – 0.8

Preheating the gel between 400Preheating the gel between 400ooC and 500C and 500ooC for C for several several hours hours is a key step. It can prevent the is a key step. It can prevent the formation of intermediate formation of intermediate αα-Fe-Fe22OO33 and obtain strontium and obtain strontium ferrite single phase with ferrite single phase with narrow size distribution at a low narrow size distribution at a low heating temperature. heating temperature. Saturation magnetization and coercive field strength Saturation magnetization and coercive field strength are are determined depending on the heat treatment of the determined depending on the heat treatment of the gel and gel and the ratio of iron and strontium in the starting the ratio of iron and strontium in the starting solution. solution. The crystal growth can be easily controlled by varying The crystal growth can be easily controlled by varying the the heat treatment in order to prepare nanocrystalline heat treatment in order to prepare nanocrystalline

hexaferrite particles with single domain behavior and hexaferrite particles with single domain behavior and a a narrow size distribution of about 7–100 nm. narrow size distribution of about 7–100 nm. The substituted ferrite can also possess hexagonal The substituted ferrite can also possess hexagonal

structure. It possesses excellent microwave structure. It possesses excellent microwave absorption absorption property with the maximum absorption property with the maximum absorption efficiency of 34.76 dB. efficiency of 34.76 dB. Aluminum substitution makes the ferromagnetic Aluminum substitution makes the ferromagnetic resonant resonant frequency of barium ferrite to increase to frequency of barium ferrite to increase to 14.56 GHz, while the 14.56 GHz, while the chromium substitution decreases chromium substitution decreases it. it.

ConclusionsConclusions

The multi-peak phenomenon arises during the The multi-peak phenomenon arises during the ferromagnetic ferromagnetic resonance, which is mostly resulting resonance, which is mostly resulting from from the spin wave the spin wave instability.instability. The lattice constants a = 5:8925 The lattice constants a = 5:8925 Å, Å, c = 23:11223 c = 23:11223 ÅÅ are are slightly influenced by chemical composition and the slightly influenced by chemical composition and the

annealed temperatures, but independent of R value. annealed temperatures, but independent of R value. TEM observation of as-burnt powders of TEM observation of as-burnt powders of Ba(MnTi)FeBa(MnTi)Fe1010OO1919 indicates that the powder particles indicates that the powder particles have an average diameter have an average diameter of 50 nm. of 50 nm. Total substitution of Fe(III) by Co(II) and Ti(IV) Total substitution of Fe(III) by Co(II) and Ti(IV) leads to a leads to a highly diluted magnetic material, highly diluted magnetic material, BaCoBaCo66TiTi66OO1919, having a very , having a very weak magnetic moment. As the weak magnetic moment. As the ratio of the Co(II)–Ti(IV) ratio of the Co(II)–Ti(IV) substitution increases, the substitution increases, the saturation magnetisation saturation magnetisation decreases from substitution of decreases from substitution of x = 1 to 6, in the system of x = 1 to 6, in the system of BaCoBaCoxxTiTixxFeFe12−2x12−2xOO1919. .

ConclusionsConclusions

The phase of Co(II)–Ti(IV)-substituted barium ferrite is The phase of Co(II)–Ti(IV)-substituted barium ferrite is found to be crystallised on the (1 1 1) planes of spinel- found to be crystallised on the (1 1 1) planes of spinel- structured iron oxide, where the micrograph shows the structured iron oxide, where the micrograph shows the distinctive angle of 70◦ between the two phases.distinctive angle of 70◦ between the two phases.

A strontium surplus is important to synthesize single A strontium surplus is important to synthesize single phase SrFephase SrFe1212OO1919 by chemical co-precipitation method. by chemical co-precipitation method. Pure ultrafine SrFePure ultrafine SrFe1212OO1919 powders (98–159 nm) were powders (98–159 nm) were obtained from precursors with Feobtained from precursors with Fe3+3+/Sr/Sr2+2+ mole ratio of mole ratio of 9.23 after annealing temperature from 900–1100 9.23 after annealing temperature from 900–1100 00C for C for 2 h in static air atmosphere. 2 h in static air atmosphere.

Increasing the pH for the precipitated precursors from Increasing the pH for the precipitated precursors from 10 to 11.5 at Fe10 to 11.5 at Fe3+3+/Sr/Sr2+2+ mole ratio of 10 increased the mole ratio of 10 increased the formation of single-phase SrFeformation of single-phase SrFe1212OO1919. .

The synthesis conditions were strongly influenced on The synthesis conditions were strongly influenced on the microstructure of the produced Sr–M ferrite the microstructure of the produced Sr–M ferrite powders. powders.

The formed ultrafine pure SrFeThe formed ultrafine pure SrFe1212OO1919 powders had good powders had good magnetic saturations (64.72–84.15 emu/g) and wide magnetic saturations (64.72–84.15 emu/g) and wide intrinsic coercivities (2937–5607 Oe).intrinsic coercivities (2937–5607 Oe).

ConclusionsConclusions

ConclusionsConclusions The saturation magnetizations are closely related to the distribution and concentration of Cr3+ ions on the five crystallographic sites. Magnetic and Mossbauer results show that Cr3+ ions preferentially occupy the octahedral 2a, 4fVI, and 12k sites. With Cr entering the Fe crystallographic sites, the saturation magnetization dramatically falls but the coercivity increases. The decrease in magnetization is therefore attributed to Cr3+ ions occupying on the spin up Fe

sites (2a and 12k sites) and magnetic dilution or non-collinear structure. It is evident that the Fe3+–O–Fe3+ super-exchange interaction may be weakened by Cr3+(3d3) substituting into some Fe(3d5) sites.

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