1) The document discusses various magnetic properties including magnetic induction, magnetic field intensity, magnetic permeability, magnetization, and the origins of magnetism. 2) It describes different types of magnetic materials including diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, and ferrimagnetic materials. 3) The domain theory of ferromagnetism is explained, including the concepts of domains, domain walls, anisotropy energy, and hysteresis in ferromagnetic materials.

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2. 1) Magnetic Induction or Magnetic Flux density (B): The
magnetic induction or magnetic flux density is the number of lines of
magnetic force passing through unit area perpendicularly. Where Φ is the
magnetic flux and A is the area of cross section. Units: Weber/m2 or Tesla.
2) Magnetic Field Intensity or Intensity of Magnetic
Field (H): Magnetic Field Intensity at any point in the magnetic field is
the force experienced by an unit north pole placed at that point. Units:
A/m.
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3. 3) Magnetic Permeability (µ): It describes the nature of the material
i.e. it is a material property. It is the ease with which the material allows
magnetic lines of force to pass through it or the degree to which magnetic
field can penetrate a given medium. Mathematically it is equal to the ratio
of magnetic induction B inside a material to the applied magnetic field
intensity H. Units: H/m.
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4. 4) Magnetization: Process of converting a non magnetic material into
magnetic sample.
5) Intensity of Magnetization (M): It is a material property. It is
defined as magnetic moment per unit volume in a material. Units: A/m.
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6. Confidential 6
Sources of Magnetic Fields

7. • Created by current through a coil:
• Relation for the applied magnetic field, H:
L
I
N
H 
applied magnetic field
units = (ampere-turns/m)
current
Magnetic Field Strength
magnetic field H
current I
N = total number of turns
L = length of the coil
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8. • Magnetic induction results in the material
Response to a Magnetic Field
current I
B = Magnetic Induction (tesla)
inside the material
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Origin of Magnetic Moment
Magnetism arises from the Magnetic Moment or
Magnetic dipole of Magnetic Materials.
When the electrons revolves around the nucleus Orbital
magnetic moment arises, similarly when the electron
spins, spin Magnetic moment arises.
The permanent Magnetic Moments can arise due to the
1.The orbital magnetic moment of the electrons
2.The spin magnetic moment of the electrons, and
3.The spin magnetic moment of the nucleus

11. Nuclear spin
Orbital motion of electrons
Origin of Magnetism Spin of electrons
A moving electric charge, macroscopically or “microscopically” is
responsible for Magnetism
Very Weak effect
Unpaired electrons required
for net Magnetic Moment
Magnetic Moment resultant from the spin of a single unpaired electron
→ Bohr Magneton = 9.273 x 1024 A/m2
Weak effect.
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Origin of Magnetic Moment

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Origin of magnetic dipoles
 The spin of the electron produces a magnetic field with a
direction dependent on the quantum number ml.

13. The spin of the electron produces a magnetic field with
a direction dependent on the quantum number ms.
Origin of magnetic dipoles
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Electrons orbiting around the nucleus create a magnetic
field around the atom.

15. Permanent
Dipoles
Alignment of
dipoles
Direction of
dipoles
Magnitudes of
dipoles
Dia magnetic
materials
Para, Ferro, Anti ferro,
Ferri magnetic materials
Para
Uniform
Ferro, Anti ferro, Ferri
Ferro Anti ferro, Ferri
Anti ferro
Ferri
Classification of magnetic Materials
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Diamagnetic Materials

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Properties
• It is a weak form of magnetism
• Diamagnetism is because of orbital magnetic moment.
• No permanent dipoles are present so net magnetic moment is zero.
• Persists only when external field is applied.
• The number of orientations of electronic orbits is such that the vector
sum of the magnetic moments is zero.
• Dipoles are induced by change in orbital motion of electrons due to
applied magnetic field.

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No Applied
Magnetic Field (H = 0)
Applied
Magnetic Field (H)
none
opposing

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• External field will cause a rotation action on the individual
electronic orbits.
• The external magnetic field produces induced magnetic
moment which is due to orbital magnetic moment.
• Induced magnetic moment is always in opposite direction of
the applied magnetic field.
• So magnetic induction in the specimen decreases.
• Magnetic susceptibility is small and negative.
• Repels magnetic lines of force.

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• Diamagnetic susceptibility is independent of temperature and
applied magnetic field strength.
• Susceptibility is of the order of -10-5.
• Relative permeability is less than one.
• It is present in all materials, but since it is so weak it can be
observed only when other types of magnetism are totally
absent.
• Examples: Bi, Zn, gold, H2O, alkali earth elements (Be, Mg,
Ca, Sr), superconducting elements in superconducting
state.

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Paramagnetic Materials

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Properties
• Possess permanent dipoles.
• If the orbital's are not completely filled or spins not balanced,
an overall small magnetic moment may exist.
• i.e. paramagnetism is because of orbital and spin magnetic
moments of the electron.
• In the absence of external magnetic field
• all dipoles are randomly oriented
• so net magnetic moment is zero.
• Spin alignment is random.
• The magnetic dipoles do not interact

24. No Applied
Magnetic Field (H = 0)
Applied
Magnetic Field (H)
random
aligned
Paramagnetic Materials
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• In presence of magnetic field the
• material gets feebly magnetized i.e. the material allows
few magnetic lines of force to pass through it.
• Relative permeability µr >1 (barely, ≈ 1.00001 to 1.01).
• The orientation of magnetic dipoles depends on temperature
and applied field.
• Susceptibility is independent of applied mag. field & depends
on temperature
• C is Curie constant

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• With increase in temperature susceptibility decreases.
• Susceptibility is small and positive.
• These materials are used in lasers.
• Paramagnetic property of oxygen is used in NMR technique
for medical diagnose.
• The susceptibility range from 10-5 to 10-2.
• Examples: alkali metals (Li, Na, K, Rb), transition metals, Al,
Pt, Mn, Cr etc.

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Ferromagnetic Materials

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Properties
• Permanent dipoles are present so possess net magnetic
moment
• Origin for magnetism in Ferro mag. Materials is due to Spin
magnetic moment of electrons.
• Material shows magnetic properties even in the absence of
external magnetic field.
• Possess spontaneous magnetization.
• Spontaneous magnetization is because of interaction between
dipoles called EXCHANGE COUPLING.

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aligned
aligned
No Applied
Magnetic Field (H = 0)
Applied
Magnetic Field (H)

33. • Magnetic susceptibility is as high as 106.
• So H << M. thus Bs = µoMs
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Magnetic
induction
B
(tesla)
Strength of applied magnetic field (H)
(ampere-turns/m)
Ferromagnetic

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• When placed in external mag. field it strongly attracts magnetic
lines of force.
• All spins are aligned parallel & in same direction.
• Susceptibility is large and positive, it is given by Curie Weiss
Law
• C is Curie constant & θ is Curie temperature.
• When temp is greater than curie temp then the material gets
converted in to paramagnetic.
• Material gets divided into small regions called domains.
• They possess the property of HYSTERESIS.
• Examples: Fe, Co, Ni.

35. Ferro magnetic Materials
Even when H = 0, the dipoles
tend to strongly align over
small patches.
When H is applied, the domains
align to produce a large net
magnetization.
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36. Thermal energy can randomize the spin
Ferromagnetic Paramagnetic
Tcurie
Heat
Tc for different materials:
Fe=1043 K, Ni=631 K,
Co=1400 K, Gd= 298 K
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37. Curie Temperature
 The temperature above (Tc) which ferromagnetic material become
paramagnetic.
 Below the Curie temperature, the ferromagnetic is ordered and
above it, disordered.
 The saturation magnetization goes to zero at the Curie
temperature.
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Antiferro magnetic
Material

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Properties
• The spin alignment is in antiparallel manner.
• So net magnetic moment is zero.
• Susceptibility depends on temperature.
• Susceptibility is small and positive.
• Initially susceptibility increases with increase in temperature
and beyond Neel temperature the susceptibility decreases with
temperature.
• At Neel temperature susceptibility is maximum.
• Examples: FeO, MnO, Cr2O3 and salts of transition elements.

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Ferri-magnetic Materials

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Classification of Ferri-magnetic
Materials
Ferrimagnetic
Materials
Cubic Ferrites
MFe2O4
Hexagonal
Ferrites
AB12O19
Garnets
M3Fe5O12

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Properties
• Special type of ferro and antiferromagnetic material.
• Generally oxides in nature.
• Ionic in nature
• Ceramic in nature so high resistivity (insulators)
• The spin alignment is antiparallel but different magnitude.
• So they possess net magnetic moment.
• Also called ferrites.
• General form MFe2O4 where M is a divalent metal ion.
• Susceptibility is very large and positive.
• Examples: ferrous ferrite, nickle ferrite

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Ion
Mn2+ 3d5
E.C Spin Orientation Net Spin S Magnetic Moment
5/2 5µB
Fe2+ 3d6 2 4µB
Co2+ 3d7 3/2 3µB
Ni2+ 3d8 1 2µB
Cu2+ 3d9 1/2 1µB

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Unpaired electrons give rise to ferromagnetism in alkali
metals
Net magnetic moment
Na 3s1
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
Ms = m. N
N = ρ NA/A

47. Ferrimagnetism
• All Fe2+ have a spin magnetic
moment.
• Half of Fe3+ have a spin moment in
one direction, the other half in the
other (decreasing the overall moment
to just that contributed by the Fe2+
ions).
Simpler picture showing a net
magnetic moment.
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48. Ferrimagnetism-Structure
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Domain Theory of Ferromagnetic
Materials

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Domain Theory of Ferromagnetism
The domain in ferromagnetic solid is understandable from
the thermo dynamical principle (i.e,) in equilibrium the
total energy of the system is minimum.
Total Energy of the domains comprises the sum of
(i) Exchange Energy (or) Magnetic Field Energy
(ii) Anisotropic Energy => Easy and Hard direction
(iii)Domain Wall Energy => Thick wall and Thin Wall
(iv) Magneto-strictive Energy

52. Exchange Energy or Magnetic Field
Energy
• The interaction energy that makes the adjacent
dipoles to align themselves is known as Exchange
Energy.
• It establishes a single domain in the ferromagnetic
material.
• It is the energy required in assembling the atomic
magnets into a single domain and this work done is
stored as potential energy.
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54. Anisotropy Energy
• Two types of directions of magnetization
• Easy Direction
• Hard Direction
• Along easy direction weak field.
• Along hard direction strong field.
• For producing same amount of magnetisation.
• The excess of energy required to magnetize the
specimen along hard direction over that required to
magnetize the specimen along easy direction is called
crystalline anistropy energy.
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55. Confidential 55

56. Domain Wall Energy or Bloch Wall
Energy
• Bloch is a transition layer which separates the adjacent
domains, magnetized in different directions.
• Based on the spin alignments Thick Wall & Thin Wall
• Thick Wall: When the spins at the boundary are
misaligned and if the direction of the spins changes
gradually. The misalignment of spins is associated with
exchange energy.
• Thin Wall: When the spins at the boundaries changes
abruptly, then the anistropic energy becomes very less.
• Ansitropy energy is directly proportional to the thickness
of the wall.
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57. • Bloch walls - The boundaries between magnetic domains.
Domain Structure and the Hysteresis Loop
• The entire change in spin direction between domains does not
occur in one sudden jump across a single atomic plane rather takes
place in a gradual way extending over many atomic planes.
Bloch Wall
• The magnetic moments in adjoining atoms change direction continuously
across the boundary between domains.
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58. Magnetostrictive Energy
• When the domains are magnatised in different directions,
they will either expand or shrink this leads to deformation
of the material, when magnetised. This phenomenon is
known as magnetostriction.
• Energy produced in this effect is called Magnetostriction
Energy.
• The deformation is different along different crystal
directions & the change in dimension depends on nature
of the material.
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Ferromagnetism
• Materials that retain a
magnetization in zero
field
• Quantum mechanical
exchange interactions
favour parallel
alignment of moments
• Examples: iron, cobalt

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• According to Becker, there are two independent
processes which take place and lead to magnetization
when magnetic field is applied.
1. Domain wall moment or Domain growth
2. Domain rotation

63. Domain wall moment or Domain wall
growth
• Volume of favorably oriented domains will increase.
• Occurs at low magnetic field.
• It is a reversible process.
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Rotation of Domains
• Rotation of less favorably oriented domains takes
place.
• Occurs at large magnetic field.
• It is a irreversible process.

64. Domain Structure and the Hysteresis Loop
1. Domain growth:
1. Each domain is magnetized in a different direction
2. Applying a field changes domain structure. Domains with
magnetization in direction of field grow.
3. Other domains shrink
2. Domain rotation:
Finally by applying very strong fields can saturate magnetization
by creating single domain Confidential 64

65. Confidential 65
Magnetic domains
• Applying very strong
fields can saturate
magnetization by
creating single domain

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Hysteresis Curve
• Means lagging or retarding of an effect behind the
cause of the effect.
• Here effect is B & cause of the effect is H.
• Also called B H curve.
• Hysteresis in magnetic materials means lagging of
magnetic induction (B) or magnetization (M) behind
the magnetizing field (H).

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68. Confidential 68
• “Domains” with
aligned magnetic
moment grow at
expense of poorly
aligned ones!
Domain Structure and the Hysteresis Loop

69. • Notice the permeability values depend upon the magnitude of H.
 When a magnetic field is first applied
to a magnetic material, magnetization
initially increases slowly, then more
rapidly as the domains begin to grow.
 Later, magnetization slows, as
domains must eventually rotate to reach
saturation.
Domain Structure and the Hysteresis Loop
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70. • Hysteresis loop - The loop traced out by magnetization in a
ferromagnetic or ferrimagnetic material as the magnetic field is
cycled. OR
• Removing the field does not necessarily return domain structure to
original state. Hence results in magnetic hysteresis.
Hysteresis Loop
Applied Magnetic
Field (H)
1. initial (unmagnetized state)
B
2. apply H, cause
alignment
4
Negative H needed to demagnitize!
. Coercivity, HC
3. remove H, alignment stays!
=> permanent magnet!
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71. Ferromagnetism: Magnetic hysteresis
Ms – Saturation
magnetization
Hc – Coercive force
(the field needed to
bring the magnetization
back to zero)
Mrs– Saturation remanent
magnetization
M
H
Mrs
Hc
Ms
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remanent magnetization = M0
coercivity = Hc

73. Domain growth reversible
boundary displacements.
Domain growth irreversible
boundary displacements.
Magnetization by
domain rotation
Hysteresis Loop
• Means lagging or retarding of an
effect behind the cause of the effect.
• Here effect is B & cause of the effect
is H.
• Also called B H curve.
• Hysteresis in magnetic materials
means lagging of magnetic induction
(B) or magnetization (M) behind the
magnetizing field (H).
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Hysteresis, Remanence, & Coercivity of
Ferromagnetic Materials

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“hard” ferromagnetic material
has a large M0 and large Hc.
“soft” ferromagnetic material
has both a small M0 and Hc.

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78. Hard versus Soft Magnets
 High initial permeability.
 Low coercivity.
 Reaches to saturation magnetization with a
relatively low applied magnetic field.
 It can be easily magnetized and demagnetized.
 Low Hysteresis loss.
 Applications involve, generators, motors,
dynamos, Cores of transformers and switching
circuits.
Characteristics of soft magnetic materials:
Soft Magnets:
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79. Importance of Soft Magnetic Materials:
 Saturation magnetization can be changed by altering composition
of the materials.
Ex:- substitution of Ni2+ in place of Fe2+ changes saturation
magnetization of ferrous-Ferrite.
 Susceptibility and coercivity which also influence the shape of the
Hysteresis curve are sensitive to the structural variables rather than
composition.
 Low value of coercivity corresponds to the easy movement of
domain walls as magnetic field changes magnitude and/ or direction.
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80. Hard versus Soft Magnets
Characteristics of Hard magnetic materials:
 Low initial permeability.
 High coercivity and High remanence.
 High saturation flux density.
 Reaches to saturation magnetization with a
high applied magnetic field.
 It can not be easily magnetized and
demagnetized.
 High Hysteresis loss.
 Used as permanent magnets.
Hard Magnets:
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81. Two important characteristics related to applications of these materials are (i)
Coercivity and (ii) energy product expressed as (BH)max with units in kJ/m3.
 This corresponds to the area of largest B-H rectangle that can be
constructed within the second quadrant of the Hysteresis curve.
 Larger the value of energy product harder is the material in terms of its
magnetic characteristics.
Schematic magnetization curve that displays hysteresis. Within
the second quadrant are drawn two B–H energy product
rectangles; the area of that rectangle labeled (BH)max is the
largest possible, which is greater than the area defined by Bd–
Hd
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Importance of Hard magnetic material

82. Who to get larger area of (BH)max i.e., who to
produce Hard magnets?
 Energy product represents the amount of energy required to demagnetize a
permanent magnet.
 Hysteresis behaviour depends upon the movement of domain walls.
 The movement of domain walls depends on the final microstructure.
Ex: the size, shape and orientation of crystal domains and impurities.
 Microstructure will depend upon how the material is processed.
 In a hard magnetic material, impurities are purposely introduced, to make
it hard. Due to these impurities domain walls cannot move easily.
 Finally the coercivity can increase and susceptibility can be decrease.
 So large external field is required to demagnetization i.e., difficult to move
the domain walls.
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83. Hard Magnetic Material Soft Magnetic Material
Have large hysteresis loss. Have low hysteresis loss.
Domain wall moment is difficult
Domain wall moment is relatively
easier.
Coercivity & Retentivity are large. Coercivity & Retentivity are small.
Cannot be easily magnetized &
demagnetized
Can be easily magnetized &
demagnetized.
Magneto static energy is large. Magneto static energy is small.
Have small values of permeability
and susceptibility
Have large values of susceptibility
and permeability.
Used to make permanent magnets. Used to make electromagnets.
Iron-nickel-aluminum alloys,
copper-nickle-iron alloys, copper–
nickel– cobalt alloys
Iron- silicon alloys, ferrous- nickel
alloys, ferrites, garnets.
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84. Confidential 84
Applications
of
Magnetic Materials

85. Confidential 85
1) Ferrite Applications
2) Magnetic Storage
Reading Process
Writing Process
Storage of data( Tapes, Floppy and Magnetic
Disc Drives)
3) Transformer
4) Motors
Magnetic materials applications

86. Magnetic materials applications
 Since ferrites have a domains & hysteresis loop they are used as
memory elements for rapid storage and retrieval of digital
information by switching the direction of magnetization in very
small toroidal cores.
 Garnets (Y3Fe5O12) are useful in microwave applications.
 Magnetic recording uses ferrite material in powder form.
 Ferrites can be used as magnets.
FERRITE APPLICATIONS
Ferrites Being Ferro-magnetic but high resistivity
eddy currents less effective
Used as transformer cores
Used as induction cores, antennas for medium and long wave broad
casting, electronic tuning, auto frequency control, FM, switching etc.
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87. Transformer Core
 Should be ceramic in nature.
 Should have very high permeability.
 The material should have very high susceptibility.
 The material should have low coresive field and low remeanent field.
 Magnetostriction should be small.
http://www.marktec.co.jp/e/product/ndt/ect/et.html
Properties:
--Best example is Iron-Silicon
alloy (97% Fe & 3% Si)
--Fe-Si (alloy) anisotropic poly
crystalline materials can develop
via plastic deformation, for
example by rolling.
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88. M V V K Srinivas Prasad; K L University
-- For body centred cubic alloys including Fe-Si alloy, the rolling texture
is (1 1 0) [0 0 1].
1/6/2024 Confidential 88

89. Magnetic Storage Devices
• Head can...
--apply magnetic field H & align
domains (i.e., magnetize the medium).
--detect a change in the magnetization
of the medium.
• Information is stored by magnetizing material due to high retentivity.
Recording Head: Soft Magnetic
Materials
Ex: Fe-Ni, Fe-Al-Si alloy, Mn-Zn
ferrite, Ni-Zn ferrite
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90. Recording Principle (Digital)
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91. How Magnetic Storage Works
 A magnetic disk's medium contains
iron particles, which can be
polarized—given a magnetic
charge—in one of two directions.
 Each particle's direction represents a
1 (on) or 0 (off), representing each bit
of data that the CPU can recognize.
 A disk drive uses read/write heads
containing electromagnets to create
magnetic charges on the medium.
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92. Confidential 92

93. Confidential 93
Magnetic Storage Devices

94. Magnetic Storage Devices
• There are two types of magnetic storage media.
• Those are particulate and thin film.
• Particulate media consist of very small needle like or acicular particles.
• Ex: γ-Fe2O3 ferrite, Co- γ- Fe2O3 ferrite and CrO2 .
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95. Thin film: It provides higher storage capacities at lower costs.
Ex: Co-Pt-Cr alloy, Co-Cr-Ta alloy (thickness 10 to 50 nm).Domains
are ~ 10-30nm! (hard drive)
• The thin film is a poly crystalline material.
• Each grain within the thin film is a single magnetic domain.
• The grain shape and size must be uniform.
Magnetic Storage Devices
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96. Magnetic Storage Devices
Thin film:
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97. Confidential 97

98. Confidential 98
Magnetic Tapes

99. Confidential 99
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

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103.  Hard magnetic materials are used.
 Motor converts electrical energy into mechanical energy.
 No heat is generated during operation.
 Motors using permanent magnets are much smaller than their
electromagnets motors.
MOTORS
http://www.animations.physics.unsw.edu.au/jw/electricmotors.html
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