magnestism

1. EXPLORING MAGNETIC
PROPERTIES OF FERRITES:
Trivial to Advanced Applications
GARIMA Kotnala

2. Nanoscience & Magnetism
 At the nanometer dimensions, a large fraction of the atoms are at
or near the surface resulting in a large surface to volume
ratio(SVR) .
 Increase in the SVR leads to increasing dominance of the
behaviour of atoms on the surface of the particle over that of
those in the interior of the particle. This affects the properties of
the particles in isolation and its interaction with other
particles. This is where quantum size effects starts playing its
role .
 Magnetism essentially results from two electronic motion
associated with the atom; the orbital motion of the electron and
the spin motion of the electron.
 On application of Magnetic field , a net alignment of these
magnetic dipoles occurs and the medium becomes magnetically
polarized.

3. MAGNETIC MATERIAL
In a magnetic material, magnetic phenomena originate due to magnetic
moment of unpaired electronic spins of atoms or ions.
Theoretical and Experimental Metal Ion Magnetic Moments
Metal Ion Theoretical
moment
Experimental
moment
Mn2+ 5 4.6
Fe2+ 4 4.1
Co2+ 3 3.7
Ni 2 2.3
Cu2+ 1 1.3
Mg 0 1.1

4. Types Of Magnetic Materials
Para
Ferro
Anti
Ferri (FERRITES)
Enforced Ferro
Those not having any
permanent magnetic
moment –
diamagnetic
materials, and those
having permanent
magnetic moment,
para, ferro, antiferro
and
ferrimagnetic(Ferrite
s) materials.

5. Magnetic Spins & Dipoles
 The Magnetic spins in solid-state materials have
enabled significant advances in current
informational and biological technologies including
information storage, magnetic sensors, bio
separation, and drug delivery
 The origin of the Magnetic potential is known as
Magnetic dipoles.
 On application of Magnetic field , a net alignment
of these magnetic dipoles occurs and the medium
becomes magnetically polarized.

6. Magnetic Interactions
 Different types of magnetic interactions which allow the magnetic
moments in solids to communicate with each other to produce a long
range order are:
 1. Magnetic dipolar interaction : Each magnetic moment of the
substance is subjected to a magnetic dipolar interaction with the other
moments. The magnetic dipolar interactions are found to be too weak to
account for the ordering of most magnetic materials with higher ordering
temperatures.
 2. Exchange interactions is the main phenomenon governing the long
range magnetic order in ferro, antiferro and ferromagnetic materials. It is
of quantum mechanical origin and electrostatic in nature. It is very strong,
but acts between neighbouring spin moments only and falls off very
rapidly with distance
 3. Direct exchange interactions: Interaction between neighbouring
magnetic dipoles proceeds directly without the help of an intennediatory.
Often direct exchange is not found to be an important mechanism in
controlling the magnetic properties because there is insufficient direct
overlap between the neighbouring 16 magnetic orbitals. Hence direct
interactions are not found to be effective in rare earth metals and
transition metals.

7. Magnetic Interactions(Contd.)
4. Indirect Exchange or Super Exchange interactions: In
ionic solids Indirect exchange or superexchange interactions
between non neighbouring magnetic ions is mediated by a
nonmagnetic ion which is placed in between the magnetic ions .
Superexchange interactions involves the oxygen orbitals as
well as metal atom (in ferrites).

8. Ferrites(M2+Fe2
3+O4
2-) )
 The term ferrite is commonly used to describe a class
of magnetic oxide compounds that contain iron oxide
as a principal component.
 Magnetite (Fe3 O4 ), also called loadstone, is a
genuine ferrite and was the first magnetic material
known to the ancient people.
 Ferrimagnetic Materials are also called Ferrites.
 Ferrites are the modified structures of iron with no
carbon and are composed of two or more sets of different
transition metals( d-block elements ; group 3 to 12).

9. Role Of Ferrites In Nanoscience
Nanoscience concerns with synthesizing, modifying and characterizing materials
having at least one spatial dimension in the size range of 1-100 nm.
Attention towards the ferrites nanomaterials is due to their great scientific and
technological importance because of the following reasons:
 Ferrites are iron containing complex oxides with technically interesting magnetic
and electrical properties.
 Development of new ferrites, enhancement of existing ferrites characteristics and
improvement of the ferrites manufacturing process began in 1950’s
 e spintronic devices, giant magnetoresistance based (GMR) sensors, magnetic
random access memories and other novel gadgets based on nanomagnetism
 There are mainly two types of ferrites called soft and hard ferrites.
 Soft ferrites are the magnetic materials that do not retain their magnetism after
being magnetized. These types of materials include cobalt, nickel, zinc,
manganese and magnesium ferrites with spinel structure. They are extensively
used in the cores of transformers where they must respond to a rapidly oscillating
field.
 Hard ferrites are permanent magnets because they can retain their magnetism
after being magnetized. For hard ferrites the loop is broad having coercivity greater
than 10 kAm-1.

10. Why Ferrites over Other
Materials?
USES AND APPLICATIONS
 Recently, ferrite materials have received extensive
applications in magnetic devices, humidity
sensors, gas sensors, catalysts,
photocatalytic hydrogen production,
pigments, and anticorrosive agents.
Applications as Sensors
 Recently, some composite oxides such as spinel
ferrite (M2+M2 3+O4 ) have attracted research
interest due to their versatile practical applications
Spinel magnetic oxides (ferrites) are very
sensitive to humidity/gases . A great advantage of
ferrites is their porosity, which is necessary for a
humidity sensor.

11. CRYSTAL STRUCTURE OF
FERRITES

12. Structure Of Ferrites
 The general chemical formula of a ferrite
molecule is M2+Fe2
3+O4
2-, where M2+
represents a divalent metal ion such as Zn2+,
Fe2+, Mg2+, Mn2+, Cd2+ etc.,
 Ferrites crystallize in the form of a cubic
structure. Each corner of a ferrite unit cell
consists of a ferrite molecule .

13. Cry
The small filled circles represent metal ions, the large open
or shaded circles represent oxygen ions: (a) tetrahedral or A
sites; (b) octahedral or B sites; and (c) one-fourth of the unit
cell of a cubic ferrite. A tetrahedron and an octahedron are
marked.
CRYSTAL STRUCTURE OF FERRITES

14. 14
i) Regular spinel structure
In this type, each divalent metal ion occupies 1 tetrahedral site and each
trivalent metal ion occupies 1 octahedral site. Totally in an unit cell, there will
be 8 tetrahedral (8 A) sites and 16 octahedral (16B) sites.
Hence, the sites A and B combined to form a regular spinel ferrite
structures as shown in Fig.
The schematic representation of zinc ferrite molecule as shown in Fig.
Fig. Regular spinel structure

15. • In a ferrite unit cell there are 8 molecules. Therefore in a
ferrite unit cell, there are 8 divalent metal ions, 16 ferric
ions and 32 Oxygen ions.
• If only the oxygen ions in ferrite crystal are
considered, it is found that they constitute a close packed
face centered cubic structure.
• In these arrangement it is found that for every four
O2 ions there are 2 octahedral sites (surrounded by 6 O2
ions) and one tetrahedral site (surrounded by4 O2 ions).
 The metal ions are distributed over these tetrahedral sites
(A sites) and octahedral sites (B sites).
 Normally there are two types of structures in ferrites.
 Regular spinel and
 Inverse spinel

16. 16
Inverse spinel structure
In this type half of the B sites (8sites) are occupied by divalent
metal ions and the remaining half of the B sites (8 sites) and
all the A sites are occupied by the trivalent metal ions, as
shown in Fig.
The schematic representation of a ferrous ferrite molecule is shown in Fig.

17. 17
The anti parallel alignment of a ferrous ferrite molecule in inverse
spinel structure is explained by the calculation of its magnetic moment. In a
ferrous ferrite molecule, there are one ferrous ion and 2 ferric ions.
When the Fe atom is ionized to form the Fe2+ ions, there are 4
unpaired 3d electrons left after the loss of two 4s electrons.
When the Fe atom is ionized to form the Fe3+ ions, there are 5
unpaired 3d electrons left after the loss of two 4s electrons and one 3d
electron. It is shown in the following electronic configuration
Ion
No. of
electrons
3d electronic
configuration
Ionic magnetic
moment
Fe 2+ 24 4µB
Fe 3+ 23 5µB


   
    
Table 3d electronic configuration of Fe2+ and Fe3+

18. Behaviour Of
Ferrites(Ferrimagnetic)
Below the Magnetization
Compensation point ,
Ferrimagnetic material is
Magnetic.
At the Compensation Point,
the magnetic Components
cancel each other.

19. Properties Of Ferrites
(M2+Fe2
3+O4
2-) )
• The susceptibility () is very large and positive. It is represented by,
 = C / (T), when T > TN
When T<TN, they behave as ferrimagnetic materials.
• Mechanically, they have pure iron character. They have low tensile
strength and are brittle and soft.
In these, all valence electrons are tied up by ironic bonding and
they are bad conductors with high resistivity of 1011  m.
• Ferrites are manufactured by powder metallurgical process by
mixing, compacting and then sintering at high temperatures
followed by age hardening in magnetic fields.
• They are soft magnetic materials and so they have low eddy
current losses and hysteresis losses.

20. EXCHANGE INTERACTION
The cooperative interaction of magnetic moments results into ferro-, ferri-
and antiferromagnetism below a critical temperature.
The energy associated with this interaction as a function of magnetic
moments of two neighboring atoms i, and j as
Depending on whether the coefficient nij is positive or negative, the magnetic
moments mi and mj tend to align parallel or antiparallel with each other,
respectively and exchange energy density
and
The ½ factor is due to summation over i & j, the interaction of each pair is
counted twice.

21. The average value of energy at temp. T is
where
Hm is the molecular or exchange field.
DOMAIN WALL
The region of the materials in which the cooperative effect extends are
known as magnetic domain. The boundaries between neighboring domains
are called domain walls. Each domain behave as a tiny magnet composed
of smaller magnets (atomic spins). Adjacent domains have their respective
spins oriented 180o or, less frequently, 90o to each other through domain
wall. Under AC magnetic field, the domain wall move in response to the
variations in the field strength resulting in alternating growth and contraction
of the domains with the changes in direction of the exciting field. The
movement of the domain walls through a magnetic material gives rise to
losses, which are usually dissipated as heat.

22. Schematic Illustration of Domain Structure at Various Stages of the
Magnetization Process

23. Variations in Hysteresis Curves
There is considerable variation in the hysteresis of different magnetic materials
In magnetic particle testing the level of residual magnetism is important. Residual
magnetic fields are affected by the permeability, which can be related to the carbon
content and alloying of the material. A component with high carbon content will have
low permeability and will retain more magnetic flux than a material with low carbon
content.

24. The hysteresis curves of two different materials are shown in the graph.
Relative to the other material, the materials with the wide hysteresis loop has :
•Lower Permeability.
•Higher Retentivity.
•Higher Coercivity.
•Higher Reluctance.
•Higher Residual Magnetism.

25. The material with the narrower loop has :
•Higher Permeability.
•Lower Retentivity.
•Lower Coercivity.
•Lower Reluctance.
•Lower Residual Magnetism.

26. Synthesis Of Ferrites
Synthesis techniques play an important role in controlling the size and
surface area of materials. The synthesis of nanoparticles of magnetic
materials (ferrites) has been reported using different chemical methods; that
is, sol-gel, sonochemical, solvothermal, precipitation, mi- croemulsion.
Sol-Gel Method
 In this method, the formation of a gel provides a high degree of
homogeneity and reduces the need for atomic diffusion during the solid-
state calcinations.[18] A solution of the appropriate precursors is formed
first, followed by conversion into a homogeneous oxide (gel) after
hydrolysis and condensation. Drying and sub- sequent calcination of the
gel yields an oxide product.
Precipitation Method
 In the precipitation method the precipitation of substances normally
soluble under the employed conditions. An inclusion occurs when the
impurity occupies a lattice site in the crystal structure of the carrier,
resulting in a crystallo- graphic defect, which can occur when the ionic
radius and charge of the impurity are similar to those of the carrier. An
occlusion occurs when an adsorbed impurity is physically trapped inside
the crystal as it grows.
Ball Milling
 A ball mill is a key piece of equipment for grinding. It is widely used for
cement, silicate products, new type building materials, fireproof materials,
chemical fertilizers, black and non- ferrous metals, glass, ceramics, etc.
Ball milling increases the surface area of a solid ma- terial and allows
preparation of the desired grain size.
Solid-State Reaction Method
 Solid-state synthesis methods are the most widely used. This method
involves mixing of raw materials and can take place with both wet and dry
processes.

27.  POWER LOSS IN IRON CORE OF TRANSFORMER/MOTOR CORE
LOSSES, EPSTEIN FRAME
 A PRECISION WEIGHT THAT FAILS THE MAGNETISIUM TEST
SHOULD NOT BE FURTHER CALIBRATED(SI STANDARDS)
REQUIREMENT MGNETIC FIELD STRENGTH AND SUSCEPTIBILITY.
 All auto vacuum valves and MPFI engine (multi point fuel injection)
automobiles uses magnetic solenoid valve.
 Magnetic field indicator for residual magnetism measurement used in air
craft industry
 All electronic watches use ferrite magnet.
 Modern car uses more than 50 magnets in its machinery
 Magnetically levitated trains(MEGLEV) with high speed & comforts without
wheels.
 Magneto-optical (MO) materials for magnetic memory applications
 World production for magnetic material is 6,28,000,00 tonnes a year.
 India produces only 0.5% of world.
IMPORTANCE OF MAGNETIC MEASUREMENT
(LEAVING APART FROM ROUTINE MEASUREMENT)

28. Example Of Versatile Ferrite-Magnesium
Magnesium
 Magnesium - Lightest among commonly used metals (􏰀 1.7
g/cm3). Melting point is 650 􏰀C and it has HCP structure.
 Is very reactive and readily combustible in air. Can be used
as igniter or firestarter.
 Pure Mg has adequate atmospheric resistance and moderate
strength.
 Properties of Mg can be improved substantially by alloying. 􏰀
Most widely used alloying elements are Al, Zn, Mn and Zr.

29. Magnesium Alloys
 Mg alloys: Impact and dent resistant, have good damping
capacity - effective for high-speed applications.
 Due to its light weight, superior machinability and ease of
casting, Mg and its alloys are used in many applications:–
Auto parts, sporting goods, power tools, aerospace
equipment, fixtures, electronic gadgets, and material
handling equipment.
 Automotive applications include gearboxes, valve
covers, alloy wheels, clutch housings, and brake
pedal brackets.

30. MAGNESIUM FERRITE AS
HUMIDITY SENSOR
Recent trend in sensor is towards ferrites as ceramic sensors a high
potential candidate due to its unique structure grain, grain boundaries,
pores and semiconducting property. This porous surface allows water
vapors to pass easily through the pores and condensation of water
vapors in capillary-like pores through grain neck. This increases the
sensivity of the humidity sensors and increases wide scope of using
ferrite material.

31. CONDUCTION MECHANISM
In humidity sensing initially chemical adsorption and dissociation
of water molecules takes place. Further adsorption leads to the
formation of H3O+ ions. Conduction occurs when H3O+ releases a
proton to neighboring water molecule, which accepts it while
releasing another proton and so forth. This is known as
Grotthuss chain reaction.
GROTTHUSS MECHANISM (Protonic Conduction)

32. Conduction on the Surface of the Material

33. In this direction we have
focused on MgFe2O4 ferrite
compound with rare earth
doping. Since magnesium
ferrite has high porosity
and electrical resistance of
the order of mega ohms.
This is desirable for
humidity sensing. The
series of samples were
prepared by doping of
cerium oxide in 2 wt%, 4
wt% & 6 wt% in pure
magnesium ferrite.
SEM pictures of pure MgFe2O4 and 4 wt% CeO2
added MgFe2O4.

34. Increase in humidity sensing of
MgFe2O4 due to CeO2 addition
For the improvement of sensitivity at lower humidity and shortening of time response
2wt%, 4wt% and 6wt% CeO2 was added in MgFe2O4. Samples were prepared by
solid state reaction method. By adding CeO2 bulk porosity of the MgFe2O4 was
increased from 2.5% to 26%.

35.  By the addition of cerium oxide the sensivity at low RH
increased and showed a better linearity than the pure
magnesium ferrite sample.
 The 4 wt% cerium oxide addition in pure magnesium
ferrite serving as nuclei for particle growth and favoring
the ripening of the particles. So that particles grow in
size and decrease in number. As a result porosity
decreases hence electrical resistance also decreases
from 51MΩ to 44MΩ.
 It exhibits a better sensitivity at low humidity values due
catalytic active cerium ions provides high surface charge
to water vapors. At higher RH values the conductivity is
dominated by more water vapor condensation into the
large canals and electrolytic conduction begins which
dominates over protonic conduction.

36. MgSO4, LiNO3, Fe(NO3)3.9H2O, NaOH and NaCl
(1-x:x:2:8:10) mixed & ground
for 50-60 min (exothermic action)
Wet Paste
Prefired at 750oC in air 3h
Powder
washed several times
heat overnight at 120oC
Dried Powder
pelletized & sintered at 850oC 2h
Rectangular Pellets (Mg1-xLixFe2O4)
Synthesis Process
NaOH convert metal
nitrates & sulfates into
hydroxides.
NaCl restricted the
growth of grains to keep
the size as small as
possible.

37. SEM micrographs of (i) pure MgFe2O4, (ii) Mg0.8Li0.2Fe2O4,
(iii) Mg0.6Li0.4Fe2O4, and (iv) Mg0.4Li0.6Fe2O4.
Humidity
response
curve
Substitution of lithium in
magnesium ferrite
enhances the smaller grain
size distribution providing
higher surface area.

38. ADVANTAGES OF FERRITES
 1. High resistivity
2. Widefrequencyrange(10kHzto50MHz) 3. Low cost
4. Large selection material
5. Shape versatility
6. Economical assembly
7. Temperature and time stability
8. High Q/small package
 Ferrites have a paramount advantage over other
types of magnetic materials: high electrical resistivity
and resultant low eddy current losses over a wide
frequency range.
 Ferrites are routinely designed into magnetic circuits
for both low- level and power applications.

39. 39
 Ferrites are used in digital computers and data processing circuits.
Ferrites are used to produce low frequency ultra sonic waves by
magnetostriction principle.
 Ferrites are widely used in non-reciprocal microwave devices. Examples
for non-reciprocal microwave devices are Gyrator, Isolator and Circulator.
 Ferrites are also used in power limiting and harmonic gyration devices.
Ferrites can also be used in the design of ferromagnetic amplifiers of
microwave signals.
 Ferrite core can be used as a bitable element.
The rectangular shape ferrite cores can be used as a magnetic shift
register.
Hard ferrites are used to make permanent magnets.
 The permanent magnets (hard ferrites) are used in instruments like
galvanometers, ammeter, voltmeter, flex meters, speedometers, wattmeter,
compasses and recorders.
APPLICATION OF FERRITES

40. Microwave Applications: Ferrite
At microwave frequency from 109 Hz region, the only bulk magnetic
materials available are ferrites. Microwave frequencies demand high-
resistivity ferrites. Mn-Zn ferrites are not used for that purpose. Ni
ferrite, Mg-Mn ferrites, and, more recently, the garnet Y3Fe5O12 have
been used for microwave applications. As in recording heads, hot
pressed and single-crystal ferrites have been produced. To keep the
resistivity high in microwave ferrites, excess Fe is avoided to eliminate
Fe2+.
Magnetic Power Loss
Concepts and
Realization of its
Measurements