The present article gives the fundamental properties magnetism, different materials, properties of different magnetic materials like, dia,para and ferro magnetic materials. The notes also explain how magnetism appear in materials, type of magnets and brief applications of magnetic materials. The materials is best for undergraduate science and engineering students and any other people of interest in magnetism

1. Magnetism
Commonly, Magnetism is a characteristic property of some materials by which, the piece of that
material contains two poles of opposite polarity called north pole (N) and south pole (S), where
like poles (N-N or S-S) repel each other and unlike poles (N-S) attract each other. The system
which contains the two poles is called as Magnet.
A Magnet always exists in two poles or it is magnetic dipole. In nature few naturally available
solid materials are magnetic. For example Load stone also called as magnetite (Fe2O3).
Every magnet develops a field around it, when materials like Iron, Cobalt and Nickel etc.
brought nearer to magnet it attracts them with a force is called magnetic Force and Materials are
called Magnetic materials. This magnetic field strength is inversely proportional to square of
distance between magnet and material.
Origin of Magnetism in materials:
 It is known that a current through the conducting wire (motion of charge or electrons) also
produce magnetic field perpendicular to direction of motion of current.
 Each electron orbiting around the nucleus (called orbital angular momentum) also acts as
current loop, hence magnetic field generates perpendicular the plane of the loop and acts as
tiny magnetic dipole. The magnetic moment of such dipole is μl (Orbital).
 As electron also spins about its own axis (spin angular momentum), hence electron also
possesses spin magnetic moment is μs. The vector sum of μl and μs gives net magnetic
dipole moment. In addition to this, atom also possesses Nuclear magnetic dipole moment but
it is very small compared to net magnetic dipole moment of electron. Hence magnetic dipole
moment of atom is considered mainly due to μl and μs only.
Orbital motion produces magnetism with momentum
μl = IA = (ev / 2r) r2 = (evr / 2)
For least non zero value, μl = ehn/4m
For spin motion μs = ehn/4m
For first orbit, n =1,
μ
orbital
nucleu
s
Orbital magnetic moment
e-
μ spin
Spin magnetic moment
e
-
I = e/T and 1/T = v/s = v/2r, for the electron
moving in an orbit, T-period of electron rotation in
orbit, e-charge of electron.
mvr = L orbital angular momentum
thus, vr = L/m also L = nh /2, where
n – orbital quantum number
h – plank’s constant, thus vr = nh /2m

2. μs = eh/4m= 9.27 x 10–24J/T is called
Bohr Magneton
 According to pauli’s exclusion principle every energy level should be filled by the electrons
in pair. But the according to Hund’s rule of electronic configuration all the energy states in
a orbital quantum number should be filled with electrons either two or one.
 In case of filling electrons in energy states (s, p, d, f etc.) one can follow Pauli’s exclusion
principle and Hund’s rule. According to Pauli’s exclusion principle each orbit in energy
states can fill two electrons of opposite spins. Before that Hund’s rule is applied according to
that first all the orbits are filled with one electron each and after second electron can be filled
in every singly filled orbit. For example in p-state six electrons are filled, means three pairs,
so that first three single electron in three places and next electrons later. In this way some
state remains unpaired in some materials. Below are some examples,
2. Bromine has 4s23d104p5 has electron configuration.
Therefore, Br has 1 unpaired electron. It is para magnetic.
3. Boran has 2s21p1 as electron configuration.
Because it has one unpaired electron, it is paramagnetic.
4. Florine - has 2s22p6 has electron configuration.
Because it has no unpaired electron, it is diamagnetic.
5. Fe2+ has 3d6 has electron configuration.
Because it has 4 unpaired electrons, it is paramagnetic with large net magnetic moment (Ferro
magnetic).
 In the elements which contain only paired electrons, the direction of spinning two electrons is
opposite to each other, these electrons produce magnetic dipole moment in opposite direction
and hence the net magnetic dipole moment cancels. But magnetic moment arises only due to
orbital motion, which always opposes the external magnetic field.

3. There are materials, in which individual atoms show a small
quantity of net magnetic moment due to presence one or two
unpaired electrons. However, due to the randomly oriented dipoles
the net magnetization is still zero in the absence of external field,
however there is a partial alignment of the atomic magnetic
moments, under the application of external magnetic field and
hence these materials move towards stronger region of field are
called Paramagnetic materials.
 The atoms in materials such as iron, cobalt and nickel have large number of unpaired
electrons; they produce large net magnetic dipole moment. As a result, each atom of these
elements acts like a very small magnet.
 Along with the net spin magnetic moments, orbital angular momentum also possesses
additional magnetic moment.
 Each of these spinning and orbital magnetic fields interacts with one another and gives net
magnetic moments along with additional nuclear magnetic moments. The net magnetic
moment of all these atoms in material gives rise to magnetism in materials.
There are different kinds of magnetic materials.
1. Diamagnetic materials 4. Paramagnetic Materials
2. Ferromagnetic materials 5. Anti ferro magnetic materials
3. Ferrimagnetic Materials.
Diamagnetic Materials:
The materials in which net spin magnetic dipole moments cancel due to presence of paired
electrons, the net magnetic moment is only due to orbital motion (ml) and magnetic moment
always opposes the external magnetic field according to Lenz’s law.
Hence the materials are always tending to move towards the weaker region of external magnetic
field from stronger one are called as Diamagnetic Materials.
These materials result net negative magnetization and negative susceptibility.
Paramagnetic Materials:
Hence these materials produce a net positive magnetization and susceptibility is slightly positive.
Ferromagnetic materials

4. In some Material presence of large density of unpaired electrons in atomic level, the magnetic
moments align with each other spontaneously because of magnetic interactions between them in
a region called a domain. Within the domain, the magnetic field is intense due strong alignment
of magnetic dipole moment due to μl and μs, but in a bulk sample the material will usually be
unmagnetized because the presence number of domains oriented in various directions.
Properties of Ferro Magnetic Materials:
 These are strongly magnetized by the application of external magnetic field.
 Ferromagnetic materials also obey the all properties of paramagnetic material but in large
extent. Magnetization is about 106 times of the paramagnetic materials.
 Ex. Iron, Cobalt and Nickel
 Relative permeability of materials is very high.
 In case of Intensity of Magnetization (I) is not directly proportional to Magnetizing field (H),
in other words permeability varies considerably with H.
 Ferromagnetic materials have a large positive value for susceptibility.
 Susceptibility of Ferromagnetic materials varies inversely as the absolute temperature; this is
known as Curie law.
 The ferromagnetism disappears if its temperature increases above certain value and the
substance becomes paramagnetic called Curie temperature and point is called Curie point.
The Curie point is 1100 C for Cobalt and 400 C for nickel and for iron is about 1043 K.
 The temperature above Curie temperature the susceptibility varies inversely as excess
temperature above the Curie point called curie Weiss law.
 Permeability (μ) decreases suddenly at Curie point.
 When ferromagnetic substance subjected to magnetic field, change in the dimension takes
place along the direction of field this phenomenon is known as MAGNETOSTRICTION.
Hence under the application external magnetic field, the
materials which possess’ large amount of net magnetic dipole
moment in the direction of applied magnetic field are called as
Ferromagnetic Materials. They show intense magnetization and
susceptibility and the magnetization will not go to zero after
removal of external field.

5.  If variable magnetic field (H) applied to Ferromagnetic materials, the variation intensity of
magnetization is not regular, this special property called Hysteresis.
INTENSITY OF MAGNETISATION:
If a magnetic material placed in a external field it will get magnetized, i.e., magnetic dipoles
orient themselves in the direction of field or substance acquired magnetic moment. The
magnetic moment acquired by the substance is equal to vector sum of magnetic moments of
individual dipoles.
Therefore Magnetic moment acquired per unit volume of specimen is Intensity of
magnetization.
Therefore 𝐼 =
𝑀
𝑉
Where V = volume of the specimen and M = magnetic moment
Unit of Intensity of magnetization is A / m,
MAGNETIC INDUCTION: When a magnetic substance (namely ‘Iron’) placed in a magnetic
field, magnetic lines of force redistribute in the specimen, therefore the resultant magnetic field
inside the specimen (Iron bar) is called Magnetic Induction or Magnetic flux Density (B).
When iron bar kept in external magnetic field, the crowding of magnetic lines takes place inside
the iron bar, hence Magnetic Induction is high for Iron. But it is least for the materials like,
glass, plastic or wood etc.
PERMIABILITY (μ) : When soft Iron bar placed in the magnetic field, magnetic lines of force
are crowding inside the specimen, means, the Iron bar greatly permits the lines of force to pass
through it, or it has large permeability than air.
Therefore the permeability of the medium may be defined as the ability of the medium to pass
magnetic lines of force. It is represented by μ.
Permeability is high for ferromagnetic materials like Iron, low for the materials like, glass,
plastic or wood etc. Permeability of air or free space is μ0 = 4 x10-7 H/m.

6. The ratio of permeability of a given material to permeability of air is known as relative
permeability, which is represented by μr.
Relative permeability for Iron is 200, Nickel is 100, for alloys of Nickel like, Permalloy 8000,
mumetal, μr for water 0.999, Bismath – 0.99984 (Dia), air – 1.000000036, Al – 1.000021 both
Para.
If the Magnetic Induction (B), Intensity of magnetizing field (H), then,
𝜇 =
𝐵
𝐻
---------------- 1
The Magnetic Induction (B), Intensity of magnetizing field (H), and Intensity of magnetization
(I) are related by the formula
B = μ0 (H + M) --------------------------- 2
Dividing both side by H, then we have 






H
M
H
B
1
Therefore, μ = μ0 (1 + χ) ---------------------------------------------- 3
Where, χ is called as susceptibility of the material.
MAGNETIC SUSCEPTIBILITY ( χ ):
Susceptibility is a constant of a material is defined as the ratio of Intensity of magnetization to
the external magnetizing field.
Hence in case of Paramagnetic and diamagnetic materials The Intensity of magnetization (I) is
directly proportional to the applied field (H). Therefore I  H or I = χ H.
The susceptibility measures the up to what extinct a magnetic material is magnetized by the
application of unit magnetizing field. It is dimensionless quantity.
Substituting μ = μ0 μr in equation (3), then μr = (1 + χ)
For free space or air χ = 0, then μr = 1
HYSTERESIS OR CYCLE OF MAGNETISATION:
When an un magnetized magnetic material E.g., Iron, subjected to variable field, the variation is
as shown in figure. As intensity magnetizing field (H) increases slowly from zero (O), the

7. intensity of magnetization also increases (I) and reaches maximum at B, it is shown by curve
OAB. If field gradually decreased from maximum (Hm) ‘I’ will also decreases, when Hm reaches
zero, I will go to zero but it retain some magnetization as shown by point C in fig.
Therefore, if a magnetic substance is magnetized, the Intensity of magnetization always
lags behind the magnetizing field on applying the reverse field. This lagging of the
magnetization behind the magnetizing field is called Hysteresis.
The complete cycle of variation of IHm is called as Hysteresis loop or cycle.
During the process of cycle of magnetization expenditure of energy is taking place, which is not
recovered This loss is referred to as Hysteresis Loss and it appears in the form heat in the
specimen.
The area of the M – H loop is the measure of Hysteresis loss per cycle per unit volume of the
specimen.
Therefore Hysteresis loss = μ0 times the area of M– H loop
Retaintivityand coercivity:
It is clear from the magnetization cycle ( M – H loop) that when magnetic field decreased from
maximum to zero the magnetization (M) has some positive or negative value.
Therefore the amount intensity of magnetization remained in the magnetic substance even after
magnetic field goes to zero is called Residual magnetism or REMANANCE.
The capacity of magnetic material to retain the magnetism after magnetizing field goes to zero is
called RETAINTIVITY.
B
C
M A
- Hm D O G Hm
H
E F
Further on application reverse field shown by OD,
the magnetization goes to zero as shown in point D,
If the reverse field is increased further the material
magnetizes in reverse direction and reaches
maximum at point E. If the reverse magnetic field
is reduced then, magnetization also reduces and
follow the path EFG as shown figure. Further
positive increase of Hm results the curve reach B to
complete one cycle.

8. If magnetic field continued to applied in reverse direction the magnetization goes to zero.
Therefore the total reverse magnetic field required remove the magnetization from the specimen
is called COERCIVE FORCE.
The capacity of a substance to retain the magnetization even after any subsequent treatment is
called COERCIVITY.
COMPARATIVE STUDY OF MAGNETIC MATERIALS
Property
Diamagnetic
substances
Paramagnetic
substances
Ferromagnetic
substances
Cause of
magnetism
Orbital motion of electrons Spin motion of electrons Formation of domains
Explanation
of magnetism
On the basis of orbital
motion of electrons
On the basis of spin and
orbital motion of electrons
On the basis of domains
formed
Behaviour In
a non-uniform
magnetic field
These are repelled in an
external magnetic field i.e.
have a tendency to move
from high to low field
region.
These are feebly attracted in
an external magnetic field
i.e., have a tendency to move
from low to high field region
These are strongly
attracted in an external
magnetic field i.e. they
easily move from low to
high field region
State of
magnetization
These are weekly
magnetized in a direction
opposite to that of applied
magnetic field
These get weekly magnetized
in the direction of applied
magnetic field
These get strongly
magnetized in the
direction of applied
magnetic field
When the
material in the
form of liquid
is filled in the
U-tube and
placed
between pole
pieces.
Liquid level in that limb
gets depressed
Liquid level in that limb rises
up
Liquid level in that limb
rises up very much
On placing
the gaseous
materials
between pole
pieces
The gas expands at right
angles to the magnetic
field.
The gas expands in the
direction of magnetic field.
The gas rapidly
expands in the direction
of magnetic field
The value of
magnetic
induction B
B < B0 B > B0 B >> B0
where B0 is the magnetic induction in vacuum

9. Magnetic
susceptibility χ
Low and negative |χ| ≈ 1 Low but positive χ ≈ 1 Positive and high χ ≈ 102
Dependence
of χ on
temperature
Does not depend on
temperature (except Bi at
low temperature)
Inversely proportional to
temperature χ ∝ 1/T
or χ= C/T.This is called Curie
law, where C = Curie constant
χ ∝ 1/T-Tc or χ = C/T-
Tc.This is called Curie
Weiss law.
Tc = Curie temperature
Dependence
of χ on H
Does not depend
independent
Does not depend independent Does not depend
independent
Relative
permeability
(μr)
μr < 1 μr > 1 μr >> 1
μr = 102
Intensity of
magnetisation
(I)
I is in a direction
opposite to that of H and
its value is very low
I is in the direction of H but
value is low
I is in the direction of H
and value is very high.
I-H curves
Magnetic
moment (M)
The value of M is very
low (χ 0 and is in a
direction opposite to H.)
The value of M is very low
and is in the direction of H
The value of M is very
high and is in the
direction of H
Transition of
materials (at
Curie
temperature)
These do not change. On cooling, these get
converted to ferromagnetic
materials at Curie temperature
These get converted into
paramagnetic materials
above Curie temperature
The property
of magnetism
Diamagnetism is found in
those materials the atoms
of which have even
number electrons
Paramagnetism is found in
those materials the atoms of
which have majority of
electron spins in the same
direction
Ferro-magnetism is found
in those materials which
when placed in an
external magnetic field
are strongly magnetised
Examples Cu, Ag, Au, Zn, Bi, Sb,
NaCl, H2O air and
diamond etc.
Al, Mn, Pt, Na, CuCl2, O2and
crown glass
Fe, Co, Ni, Cd, Fe3O4 etc.

10. SOFT MAGNETIC MATERIALS:
The MAGNETIC MATERIALS are easily magnetized and de-magnetized on application of
magnetic field are called soft magnetic materials.
They are characterized by a thin hysteresis loop. It is imperative that soft magnetic materials
should have high initial permeability and a low coercivity. Due to smaller area of hysteresis loop
loss of energy is greatly reduced, hence material can be used in higher frequencies.
,
Applications:
1. These are used as cores of transformers, motors and generators. Electrical steel is used
for manufacturing cores.
2. Ni-Fe alloys and soft ferrites are used in transformers and inductors which are used in
communication equipment.
3. Soft ferrites and garnets are used in the Microwave system components.
4. In magnetic amplifier, storable core devices, computers these materials used as Square
loop materials.
HARD MAGNETIC MATERIALS:
THE MAGNETIC MATERIALS which offered high resistance to demagnetize are called soft
magnetic materials. They are characterized by a thick hysteresis loop. It is imperative that soft
magnetic materials should have high permeability, high coercivity and remanence. Due to
smaller area of hysteresis loop loss of energy is greatly reduced; hence material can be used in
higher frequencies.

11. 1. These are used in case of magnetic memory discs in computers.
2. These are used in the Magnetic resonance and Superconducting magnetic applications.
3. They are used in Amplifiers and other electronic devices.
DIFFERENCES BETWEEN HARD AND SOFT MAGNETIC MATERIALS
Hard Magnetic Materials Soft Magnetic Materials
1. Materials which retain their magnetism and are
difficult to demagnetize are called hard magnetic
materials.
These materials retain their magnetism even after
the removal of the applied magnetic field. Hence
these materials are used for making permanent
magnets. In permanent magnets the movement of
the domain wall is prevented. They are prepared
by heating the magnetic materials to the required
temperature and then quenching them. Impurities
increase the strength of hard magnetic materials.
1. Soft magnetic materials are easy to
magnetize and demagnetize.
These materials are used for making
temporary magnets. The domain wall
movement is easy. Hence they are easy to
magnetize. By annealing the cold worked
material, the dislocation density is reduced
and the domain wall movement is made
easier. Soft magnetic materials should not
possess any void and its structure should be
homogeneous so that the materials are not
affected by impurities.
2. They have large hysteresis loss due to large
hysteresis loop area.
2. They have low hysteresis loss due to
small hysteresis area.
3. Susceptibility and permeability are low. 3. and permeability are high.
4. and retentivity values are large. 4. Coercivity and retentivity values are less.
5. Magnetic energy stored is high. 5. Since they have low retentivity and
coercivity, they are not used for making
permanent magnets.
5. They possess high value of BH product. 6. Magnetic energy stored is less.
7. The eddy current loss is high. 7. The eddy current loss is less because of
high resistivity.
Ferrites: Ferrites are chemical compounds consisting of ceramic materials with iron(III) oxide
(Fe2O3) as their principal component. Many of them are magnetic materials and they are used to
make permanent magnets, ferrite cores for transformers, and in various other applications.
Many ferrites are spinels with the formula AB2O4, where A and B represent various metal
cations, usually including iron. Spinel ferrites usually adopt a crystal motif consisting of cubic

12. close-packed (fcc) oxides (O2−) with A cations occupying one eighth of the tetrahedral holes and
B cations occupying half of the octahedral holes—that is, the inverse spinel structure.
The magnetic material known as "ZnFe" has the formula ZnFe2O4, with Fe3+ occupying the
octahedral sites and half of the tetrahedral sites. The remaining tetrahedral sites in this spinel are
occupied by Zn2+.
Some ferrites have hexagonal crystal structure, e.g. barium ferrite BaO:6Fe2O3 or BaFe12O19.
Ferrites are usually non-conductive ferrimagnetic ceramic compounds derived from iron oxides
such as hematite (Fe2O3) or magnetite (Fe3O4) as well as oxides of other metals. Ferrites are, like
most other ceramics, hard and brittle. In terms of their magnetic properties, the different ferrites
are often classified as "soft" or "hard", which refers to their low or high magnetic coercivity.
Applications of Ferrites:
Ferrite cores are used in electronic inductors, transformers, and electromagnets where the high
electrical resistance of the ferrite leads to very low eddy current losses. They are commonly seen
as a lump in a computer cable, called a ferrite bead, which helps to prevent high frequency
electrical noise (radio frequency interference) from exiting or entering the equipment.
Early computer memories stored data in the residual magnetic fields of hard ferrite cores, which
were assembled into arrays of core memory. Ferrite powders are used in the coatings of magnetic
recording tapes. One such type of material is iron (III) oxide.
Ferrite particles are also used as a component of radar-absorbing materials or coatings used in
stealth aircraft and in the absorption tiles lining the rooms used for electromagnetic compatibility
measurements.
Most common radio magnets, including those used in loudspeakers, are ferrite magnets. Ferrite
magnets have largely displaced Alnico magnets in these applications.
It is a common magnetic material for electromagnetic instrument pickups, because of price and
relatively high output. However, such pickups lack certain sonic qualities found in other pickups,
such as those that use Alnico alloys or more sophisticated magnets.[citation needed]
Ferrite nanoparticles exhibit super paramagnetic properties.

13. APPLICATIONS OF MAGNETIC MATERIALS:
1) The Hysteresis: The Hysteresis curves are used to determine the loss of energy for ex. Soft
iron has relatively offers less Hysteresis loss compared to steel. Hence one can judge
suitability of materials for different applications.
2) Transformer cores: Transformer cores are made of high permeability for poor magnetic
material also because large amount flux can pass through core, and have low Hysteresis loss,
because in this process the material undergo series of cycles of magnetization and produce
the heat at each time. For Ex Mu metal (Ni and Fe with small amount of Cu and Cr), Perm
alloy (Fe and Ni)
3) Diaphragms of telephones are made of stalloy, which is an alloy of Fe and Si. Ferromagnetic
materials also used as cores of motors and dynamos
4) Permanent magnets are made of magnetic materials having high Retentivity and high
coercivity. Their Hysteresis loss need not be considered as permanent magnets are rarely
taken through cycles of magnetization. Hence Cobalt Steel and Tinconal are used.
5) Magnetostriction oscillators working on the principle of Magnetostriction, used to produce
the Ultrasonic waves here ferromagnetic materials.
6) The semi conducting ferromagnetic materials called ferrites have number of application in so
many electronic industries.
7) The electromagnets are made of materials which have a high susceptibility at low
magnetizing fields and have low coercivity and low residual magnetism.
8) Ferromagnetic materials are used in electrical circuits to shield components from stray
magnetic fields of currents. The components are placed within the cavity of a hallow
ferromagnetic cylinder. The magnetic lines of force are conducted through the shield
because of its high permeability. As a result the cavity is relatively free from the effects of
external magnetic fields.