2. Magnets
 A magnet (from Greek μαγνήτις λίθος magnḗtis líthos, "
Magnesian stone") is a material or object that produces a
magnetic field. It attracts ferrous objects like pieces of
iron, steel, nickel and cobalt. This magnetic field is
invisible but is responsible for the most notable property
of a magnet: a force that pulls on other ferromagnetic
materials, such as iron, and attracts or repels other
magnets.
 A magnet can be made to stick to objects which
contain magnetic material such as iron, even if they
are not magnets. But a magnet cannot be made to
stick to materials which are plastic, or cotton, or any
other material, such as silicate rock, which is not
magnetic.

3. TYPES OF MAGNET
 Permanent
magnets
 ELECTROMAGNETS

4. Permanent magnets
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 A permanent magnet is an object made from a material that
is magnetized and creates its own persistent magnetic field.
 Alloys of iron, nickel, cobalt, gadolinium and certain
ceramic materials can become "permanent" magnets,
such that they retain their magnetism for a long time.

5. Strongest Type of Permanent Magnet
A neodymium magnet (also known as NdFeB, NIB, or Neo magnet), the most
widely-used type of rare-earth magnet, is a permanent magnet made from an
alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline
structure. Developed in 1982 by General Motors and Sumitomo Special Metals,
neodymium magnets are the strongest type of permanent magnet made. They
have replaced other types of magnet in the many applications in modern
products that require strong permanent magnets, such as motors in cordless
tools, hard disk drives, and magnetic fasteners.
Nickel plated neodymium magnet Nickel-plated neodymium magnet cubes
on a bracket from a hard drive.

6. Permanent magnets

7. Permanent Ferrite Magnet
 Magnets that are commonly used in speakers

8. Application of magnets:
G a us s C a nnon
• There are 3 ball bearings stuck to a magnet in a track. A
fourth ball bearing is released on the opposite side of the
magnet, and is attracted to it. The ball at the other end
shoots off at a much higher velocity.
• A second version of the gauss cannon is below and uses one
spherical magnet which looks identical to the ball bearings. The
device can first be shown without the magnet, when it acts like
Newton's cradle and conserves energy. With the magnet, the end ball
shoots off the end of the ramp.

9. Application of magnets:
Barkhausen effect
In the Barkhausen effect, a large coil of fine wire is
connected through an amplifier to a speaker. When
an iron rod is placed within the coil and stroked with
a magnet, an audible roaring sound will be produced
from the sudden realignments of the magnetic
domains within the rod. A copper rod, on the other
hand, produces no effect.

10. • A good permanent magnet should produce a high magnetic
field with a low mass, and should be stable against the
influences which would demagnetize it. The desirable
properties of such magnets are typically stated in terms of the
remanence and coercivity of the magnet materials.

11. R e ma ne nc e
 Remanence or remanent ma gnetization is the
magnetization left behind in a ferromagnetic material (such
as iron) after an externalmagnetic field is removed. It is
also the measure of that magnetization. Colloquially, when
a magnet is "magnetized" it has remanence.The
remanence of magnetic materials provides the magnetic
memory in magnetic storage devices, and is used as a
source of information on the past Earth's magnetic field in
paleomagnetism.
 The equivalent term residual ma gnetization is generally
used in engineering applications. In transformers,
electric motors and generators a large residual
magnetization is desirable . In many other applications it is
an unwanted contamination, for example a magnetization
remaining in an electromagnet after the current in the coil
is turned off. Where it is unwanted, it can be removed by
degaussing.
 Sometimes the term retentivity is used for remanence
measured in units of magnetic flux density.

12. Types of remanence
Saturation remanence
 The default definition for remanence is the magnetization remaining in zero
field after a large magnetic field is applied (enough to achievesaturation).[1] A
magnetic hysteresis loop is measured using instruments such as a
vibrating sample magnetometer and the zero-field intercept is a measure of
the remanence. In physics this measure is converted to an average
magnetization (the total magnetic momentdivided by the volume of the sample)
and denoted in equations as Mr. If it must be distinguished from other kinds of
remanence it is called the saturation remanence or saturation
isothermal remanence (SIRM) and denoted by Mrs.
 In engineering applications the residual magnetization is often measured using
a B-H Analyzer, which measures the response to an AC magnetic field (as in
Fig. 1). This is represented by a flux density BR. This value of remanence is one
of the most important parameters characterizing permanent magnets; it
measures the strongest magnetic field they can produce. Neodymium magnets
, for example, have a remanence approximately equal to 1.3 teslas.

13. Is o t h e r m a l r e m a n e n c e
 Often a single measure of remanence does not provide adequate
information on a magnet. For example, magnetic tapes contain a large
number of small magnetic particles, and these particles are not identical.
Magnetic minerals in rocks may have a wide range of magnetic
properties. One way to look inside these materials is to add or subtract
small increments of remanence. One way of doing this is first
demagnetizing the magnet in an AC field, and then applying a field H and
removing it. This remanence, denoted by Mr(H), depends on the field. It is
called the initial remanence or the isothermal remanent
magnetization (IRM) .
 Another kind of IRM can be obtained by first giving the magnet a
saturation remanence in one direction and then applying and removing a
magnetic field in the opposite direction. This is calleddemagnetization
remanence or dc demagnetization remanence and is denoted by
symbols like Md(H), where H is the magnitude of the field. Yet another
kind of remanence can be obtained by demagnetizing the saturation
remanence in an ac field. This is called ac demagnetization
remanence or alternating field demagnetization remanence and
is denoted by symbols like Maf(H).
 If the particles are noninteracting single-domain particles with uniaxial
anisotropy, there are simple linear relations between the remanences.

14. Anhysteretic remanence
 Another kind of laboratory remanence is 'anhysteretic
remanence or anhysteretic remanent magnetization (ARM). This
is induced by exposing a magnet to a large alternating
field plus a small dc bias field. The amplitude of the
alternating field is gradually reduced to zero to get
ananhysteretic magnetization, and then the bias field is
removed to get the remanence. The anhysteretic
magnetization curve is often close to an average of the
two branches of the hysteresis loop, and is assumed in
some models to represent the lowest-energy state for a
given field. ARM has also been studied because of its
similarity to the write process in some magnetic recording
technology and to the acquisition of
natural remanent magnetization in rocks.

15. Coercivity
 In materials science, the coercivity, also called the coercive field or coercive
force, of aferromagnetic material is the intensity of the applied magnetic field
required to reduce the magnetization of that material to zero after the
magnetization of the sample has been driven tosaturation. Thus coercivity
measures the resistance of a ferromagnetic material to becoming
demagnetized. Coercivity is usually measured in oersted or ampere/meter units
and is denoted HC. It can be measured using a B-H Analyzer or magnetometer.
 Ferromagnetic materials with high coercivity are called
magnetically hard materials, and are used to make permanent magnets.
Permanent magnets find application in electric motors, magnetic recording
media (e.g. hard drives, floppy disks, or magnetic tape) and magnetic separation
.
 Materials with low coercivity are said to be magnetically soft. They are used in
transformer andinductor cores, recording heads. microwave devices, and
magnetic shielding.

16. Experimental determination
 Typically the coercivity of a magnetic material is determined by measurement of
the hysteresis loop, also called the magnetization curve, as illustrated in the figure.
The apparatus used to acquire the data is typically a vibrating-sample or
alternating-gradient magnetometer. The applied field where the data line crosses
zero is the coercivity. If an antiferromagnet is present in the sample, the coercivities
measured in increasing and decreasing fields may be unequal as a result of the
exchange bias effect.
 The coercivity of a material depends on the time scale over which a magnetization
curve is measured. The magnetization of a material measured at an applied
reversed field which is nominally smaller than the coercivity may, over a long time
scale, slowly relax to zero. Relaxation occurs when reversal of magnetization by
domain wall motion is thermally activated and is dominated by magnetic viscosity.[2]
The increasing value of coercivity at high frequencies is a serious obstacle to the
increase ofdata rates in high-bandwidth magnetic recording, compounded by the
fact that increased storage density typically requires a higher coercivity in the
media.
 The coercivity of a material depends on the time scale over which a magnetization
curve is measured. The magnetization of a material measured at an applied
reversed field which is nominally smaller than the coercivity may, over a long time
scale, slowly relax to zero. Relaxation occurs when reversal of magnetization by
domain wall motion is thermally activated and is dominated by magnetic viscosity.[2]
The increasing value of coercivity at high frequencies is a serious obstacle to the
increase ofdata rates in high-bandwidth magnetic recording, compounded by the
fact that increased storage density typically requires a higher coercivity in the
media.

17. Material Coercivity [Oe]
[.1Mn:]6Fe:27Ni:Mo, Supermalloy 0.002
Fe:4Ni, Permalloy 0.01–1
.9995 iron–filings 0.05–470
11Fe:Si, silicon iron 0.4–0.9
Raw iron 2 (1896)
.99 Nickel 0.7–290
Zn ,
xFeNi1-xO3
15–200
ferrite for magnetron
2Fe:Co, Iron pole 240
>.99 cobalt 10–900
6
6Al:18Fe:8Co:Cu:6Ni–
3Ti:8Al:20Fe:20Co:2Cu:8Ni, 640–2000
alnico 5–9, fridge magnet and stronger
Cr:Co:Pt,
1700
disk drive recording media
2Nd:14Fe:B, neodymium-iron-boron 10,000–12,000
12Fe:13Pt, Fe48Pt52 12,300+[1]
?(Dy,Nb,Ga,Co):2Nd:14Fe:B 25,600–26,300
2Sm:17Fe:3N, samarium-iron-nitrogen <500–35,000 (10 K)

18. ELECTROMAGNET
S

19. An
electromagnet
 A soft iron rod has no
magnetic field
 When current flows in
the wire the soft iron
becomes magnetized so a
magnetic field is detected
by the plotting
compasses.
 The magnetic field
disappears when the
current is turned off.

20.  Electromagnetic radiation (often abbreviated E-M
radiation or EMR) is a form of energy that exhibits wave-like
behavior as it travels through space. EMR has both electric and
magnetic fieldcomponents, which oscillate in phase
perpendicular to each other and perpendicular to the direction
of energy propagation.

21. Uses of Electromagnets in the Medical Field
 Electromagnets are also widely used in the
medical field. They are mainly used in removing
embedded magnetic metal particles from inside
the eyes, usually deposited during an accident.
One of the most important uses of
electromagnet in hospital is in magnetic
resonance imaging (MRI), which is used for
getting a detailed image of the inside of the
body to diagnose a number of diseases.

22. magnetic resonance imaging (MRI)

23. Technological Uses of Electromagnets
 The main technological uses of electromagnets are in storing information and
moving things. They are used in many electrical devices like electrical balls,
loudspeakers, magnetic locks and various magnetic recording devices such as
computer disks, tape recorders, VCR, etc. Televisions also uses
electromagnets to power the cathode ray tube to regulate the direction of the
beam of electrons, used to illuminate the screen. Electromagnets are also
used in telephones, mobile phones and doorbells. Moving metals and picking
up cars in junkyards are some of the common everyday uses of
electromagnets. Spacecraft also use electromagnets in the propulsion system
to generate power.
Electromagnets are also used for dumping garbage in recycling plants. Some
studies are being carried out to discover the potential of using electromagnets
in developing electric cars. The possibility of using electromagnetism in
developing more environmental friendly or less polluting energy storage
systems, is also a subject of many studies.

24. Common Uses Of Magnets:
Magnetic Recording Data
Common T.V. and Computer Monitors
Credit, Debit and ATM cards

28. Magnetic Fields
 The region where the magnetic forces act is
called the “magnetic field”

29. • A compass table with a hundred or so tiny
compass needles displays the magnetic
field of a bar magnet, or two attracting or
repeling magnets, for overhead projection.

30. A piece of lodestone picks up small iron objects, or
can be suspended so as to point north.

31. EARTH’S
MAGNETISM
The Earth itself has a huge
magnetic field - as if it had a
huge bar magnet embedded
at its centre. The Earth’s
magnetic field lines emerge
from near the geographical
north pole and re-enter it at
the south pole. The nature of
the field around the Earth
varies in both strength and
direction. The Earth’s
magnetic field is strongest at
the magnetic poles and
weakest near the Equator.

32. Why does the Earth have a magnetic field?
The Earth has, at its centre, a
dense liquid core, of about
half the radius of the Earth,
with a solid inner core. This
core is though to be mostly
made of molten iron and
nickel perhaps mixed with
some lighter elements.
Circulating ions of iron and
nickel in highly conducting
liquid region of earth’s core
might be forming current
loops and producing earth’s
magnetism.

33. The Earth’s magnetic field

34. Magnetic
eleMents
 Magnetic Declination
 Magnetic Inclination or Magnetic Dip

35. Magnetic Declination
The small angle
between magnetic
axis and
geographic axis at
a place is defined
as the magnetic
declination.

36. Magnetic Inclination or
Magnetic Dip
The angle which
the direction of
total strength of
earth’s magnetic
field makes with
a horizontal line
in magnetic
meridian.

37. M a g n e t ic P r o p e r t ie s o f
A to ms
 Atoms themselves have magnetic properties
due to the spin of the atom’s electrons.
 Groups of atoms join so that their
magnetic fields are all going in the same
direction
 These areas of atoms are called “domains”

38. When an unmag netized s ubs tance is placed in a mag netic
field, the s ubs tance can become mag netized.
This happens when the s pinning electrons line up in the
s ame direction.

39.  The metals affected by
magnetism consist of tiny
regions called 'Domains'
(.wav)
which behave like tiny
magnets. Normally they are
arranged in the magnetic
material all pointing in
different directions in a
completely random fashion
and so their magnetic effects
cancel each other out. If an
object is magnetized it is
because the domains are all
made to point in the same
direction. This can be done by
stroking the magnetic
material with a magnet (or
magnets) as shown in the
diagram. When aligned the
domains reinforce one
another and create north and
south poles at either end.

40. Classification of magnetic
materials
 Materials respond differently to the force of
a magnetic field. There are three main
classifications of magnetic materials. A
magnet will strongly attract ferromagnetic
materials, weakly attract paramagnetic
materials and weakly repel diamagnetic
materials.

41. Classification of magnetic
materials
 Diamagnetic Substances
 Paramagnetic substances
 Ferromagnetic substances

42. Diamagnetic substances
• The diamagnetic substances are those in
which the individual atoms or ions do not
possess any net magnetic moment on
their own.
• When such substances are placed in an
external magnetizing field, they get feebly
magnetized in a direction opposite to a
magnetizing field.

43. • Certain materials are diamagnetic, which
means that when they are exposed to a strong
magnetic field, they induce a weak magnetic
field in the opposite direction. In other words,
they weakly repel a strong magnet.
• Diamagnetic materials have a weak, negative
susceptibility to magnetic fields. Diamagnetic
materials are slightly repelled by a magnetic
field and the material does not retain the
magnetic properties when the external field is
removed. In diamagnetic materials all the
electron are paired so there is no permanent
net magnetic moment per atom. Diamagnetic
properties arise from the realignment of the
electron paths under the influence of an
external magnetic field. Most elements in the
periodic table, including copper, silver, and
gold, are diamagnetic.

44. Strongest Diamagnetic materials
• Bismuth and carbon graphite are the
strongest diamagnetic materials. They
are about eight times stronger than
mercury and silver. Other weaker
diamagnetic materials include water,
diamonds, wood and living tissue. Note
that the last three items are carbon-
based.
• The electrons in a diamagnetic material
rearrange their orbits slightly creating
small persistent currents, which oppose
the external magnetic field.

45. Uses of Diamagnetic materials
• Although the forces created by diamagnetism are
extremely weak—millions of times smaller than the
forces between magnets and ferromagnetic materials
like iron, there are some interesting uses of those
materials.
Curving water
• A thin layer of water laying on the top surface of a
very power magnet will be slightly repelled by the
magnetic field. This can be verified by viewing the
reflection off the water surface and seeing a slight
dimple on the surface.
Used in levitation
• The most popular application of diamagnetic materials
is magnetic levitation, where an object will be made to
float in are above a strong magnet. Although most
experiments use inert objects, researchers as the
University of Nijmegen in the Netherlands
demonstrated levitating a small frog in a powerful
magnetic field.

46. Levitating pyrolytic graphite

47. Paramagnetic Substances
 Paramagnetic substances are those in
which each individual atom or molecule or
ion has a net non zero magnetic moment
of its own.
 When such substances are placed in an
external magnetic field, they get feebly
magnetized in the direction of the
magnetizing field.

48.  Paramagnetic materials are metals that are
weakly attracted to magnets. Aluminum and
copper are such metals. These materials can
become very weak magnets, but their
attractive force can only be measured with
sensitive instruments.
 Temperature can affect the magnetic
properties of a material. Paramagnetic
materials like aluminum, uranium and
platinum become more magnetic when they
are very cold.
 The force of a ferromagnetic magnet is
about a million times that of a magnet made
with a paramagnetic material. Since the
attractive force is so small, paramagnetic
materials are typically considered
nonmagnetic.

49.  Paramagnetic materials have a small,
positive susceptibility to magnetic
fields. These materials are slightly
attracted by a magnetic field and the
material does not retain the magnetic
properties when the external field is
removed. Paramagnetic properties are
due to the presence of some unpaired
electrons, and from the realignment of
the electron paths caused by the
external magnetic field. Paramagnetic
materials include magnesium,
molybdenum, lithium, and tantalum.

50. Ferromagnetic materials
Ferromagnetic
Domains in
Materials Ferromagnetic
material are those
in which each
individual atom or
molecule has a
non zero magnetic
moment

51. • Ferromagnetic materials have a large, positive
susceptibility to an external magnetic field. They
exhibit a strong attraction to magnetic fields and are
able to retain their magnetic properties after the
external field has been removed. Ferromagnetic
materials have some unpaired electrons so their atoms
have a net magnetic moment. They get their strong
magnetic properties due to the presence of magnetic
domains. In these domains, large numbers of atom's
moments (1012 to 1015) are aligned parallel so that the
magnetic force within the domain is strong. When a
ferromagnetic material is in the unmagnified state, the
domains are nearly randomly organized and the net
magnetic field for the part as a whole is zero. When a
magnetizing force is applied, the domains become
aligned to produce a strong magnetic field within the
part. Iron, nickel, and cobalt are examples of
ferromagnetic materials. Components with these
materials are commonly inspected using the magnetic
particle method.

52. Ferromagnets
• A ferromagnetic material is one that has
magnetic properties similar to those of iron.
In other words, you can make a magnet out
of it. Ferromagnetic materials are strongly
attracted by a magnetic force. The elements
iron (Fe), nickel (Ni), cobalt (Co) and
gadolinium (Gd) are such materials.
• Magnetic fields come from currents. This is
true even in ferromagnetic materials; their
magnetic properties come from the motion
of electrons in the atoms. Each electron has
a spin. This is a quantum mechanical
phenomenon that is difficult to make a
comparison to, but can be thought of as
similar to the rotation of the Earth about its
axis.

53. Iron and steel
• Iron is the most common element associated
with being attracted to to a magnet. Steel is
also a ferromagnetic material. It is an alloy or
combination of iron and several other metals,
giving it greater hardness than iron, as well as
other specialized properties. Because of its
hardness, steel retains magnetism longer than
iron.

54. TWO FORMS OF IRON :
• Soft Iron , If you were hit on the head with
a soft iron bar, it would still feel very hard;
soft is simply a term describing the
magnetic properties. In hard iron, the
domains will not shift back to their starting
points when the field is taken away. In soft
iron, the domains return to being randomly
aligned when the field is removed.
• Hard iron is used in permanent magnets. To
make a permanent magnet, a piece of hard
iron is placed in a magnetic field. The
domains align with the field, and retain a
good deal of that alignment when the field
is removed, resulting in a magnet.

55. blade with soft
iron
soft iron wire Soft Iron, Stainless Steel

56. CURIE TEMPERATURE
The Curie temperature (Tc) is the critical temperature
beyond which a previously ferromagnetic material becomes
paramagnetic. On the atomic level, below the Curie
temperature the magnetic moments, contributed mainly by
the electrons, are alligned in their respective domains and
even a weak external field results in a net magnetization. As
the temperature increases to Tc and above however,
fluctuations due to the increase in thermal energy destroy
that allignment. Tc for nickel is 631K, while that for iron is
1043K.

57. CURIE TEMPERATURE:
Curie temperature in ferromagnetic and
ferrimagnetic materials.
Substance Curie
temp °C
Iron (Fe) 770
Cobalt (Co) 1130
Nickel (Ni) 358
Iron Oxide 622
(Fe2O3)

58. Magnetizing ferromagnets
Ferromagnetic materials can be magnetized in the following
ways:
• Heating the object above its Curie temperature, allowing it to
cool in a magnetic field and hammering it as it cools. This is
the most effective method and is similar to the industrial
processes used to create permanent magnets.
• Placing the item in an external magnetic field will result in the
item retaining some of the magnetism on removal. Vibration
has been shown to increase the effect. Ferrous materials
aligned with the Earth's magnetic field that are subject to
vibration (e.g., frame of a conveyor) have been shown to
acquire significant residual magnetism.
• Stroking: An existing magnet is moved from one end of the
item to the other repeatedly in the same direction.

59. Demagnetizing ferromagnets
Magnetized ferromagnetic materials can be demagnetized (or degaussed) in the
following ways:
• Heating a magnet past its Curie temperature; the molecular motion destroys the
alignment of the magnetic domains. This always removes all magnetization.
• Placing the magnet in an alternating magnetic field with an intensity above the
material's coercivity and then either slowly drawing the magnet out or slowly
decreasing the magnetic field to zero. This is the principle used in commercial
demagnetizers to demagnetize tools and erase credit cards and hard disks and
degaussing coils used to demagnetize CRTs.
• Some demagnetization or reverse magnetization will occur if any part of the
magnet is subjected to a reverse field above the magnetic material's coercivity.
• Demagnetisation progressively occurs if the magnet is subjected to cyclic fields
sufficient to move the magnet away from the linear part on the second quadrant
of the B-H curve of the magnetic material (the demagnetisation curve).
• Hammering or jarring: the mechanical disturbance tends to randomize the
magnetic domains. Will leave some residual magnetization.

60. Hysteresis curve
Magnetic Saturation
 The relationship between magnetic field
strength (H) and magnetic flux density (B) will
follow a curve up to a point where further
increases in magnetic field strength will result
in no further change in flux density. This
condition is called magnetic saturation till
point (a).

61. R e te n
t it y
• the plotted relationship will follow a
different curve back towards zero field
strength at which point it will be offset
from the original curve by an amount
called the remanent flux density or
Retentity as shown in graph at point (b)
• The 'thickness' of the middle, describes
the amount of hysteresis, related to the
coercivity of the material as from (c) to (f)

65. Hysteresis curve of soft Iron and steel
 The retentivity of soft
iron > retentivity of
steel
 Soft iron is more
strongly magnetized
than steel
 Coercivity of soft iron <
Coercivity of steel
 Hence, soft iron loses its
magnetism more rapidly
than steel does.

66. THE END

67. ción !!!
ua ten
p or s
rac ias
G

68. CREATIVE MAKER:
MARK ANTHONY B. ENOY
BS EE – III

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