Different Types:
Magnetic materials are mainly 3 kinds by thedirection of induced flux and the stability of these.
That's are,
1. Diamagnetic materials
E.g: Cadmium, Copper, Silver,
Bismuth, Tin, zinc, Gold, Niobium and its
compounds.
2. Paramagnetic materials
E.g: Aluminum, Calcium, Oxygen,
Platinum, Titanium and Chromium.
3. Ferromagnetic materials
E.g:
a. Ferromagnetic materials
E.g: Iron, Cobalt, Nickel
b. Anti-ferro magnetic materials
E.g: Ferrous oxide,
Manganese oxide, Zinc ferrite
c. Ferrimagnetic materials
E.g: Nickel ferrite, Manganese
ferrite, Ferrous ferrite
Diamagnetic Materials:
Definition:
These materials when placed in a
magnetic field, becomes weakly
magnetized in the direction opposite to
that of the applied field. There is no
permanent dipole moment in each atom.
The induced magnetic moment produced
in these materials during the application
of the external magnetic field decreases
the magnetic induction present in the
specimen.
Origin
A material contains a large number
of electrons and the orbits of these
electrons are randomly oriented in space.
The current that is produced due to
movement of electron in an orbit
produces magnetic field in a direction at
right angles to the plane of the orbit. This
magnetic field induces a magnetic
moment in the atom in a direction
opposite to it. These magnetic moments
are randomly oriented. Hence the
magnetic moments of all such electron
gets cancelled resulting in the net
magnetism equal to zero in the material.
When an external magnetic field is
applied to the material, rotation of
dipoles take place producing an induced
dipole moment: This induced dipole
moment opposes the applied field. The
magnetism which is created in a
direction opposite to that of the external
field is called diamagnetism.
Characteristics of diamagnetic materials:
1. Susceptibility ( m) of a diamagnetic
material is always negative. The relative
permeability μr < 1.
Example For Cadmium, ( m) = - 0.18 x10 -6
For Copper, ( m ) = - 0.086 x10 -6
For Silver, ( m ) = - 0.2 x10 -6
2. When magnetic field is applied, it
repels the magnetic lines of force. This
property is exhibited by
superconductors. Hence we call all
superconducting materials (at low
temperature) as perfect diamagnet. When
the temperature is increased beyond it
critical temperature, diamagnetism
suddenly disappears and it behaves like a
normal conducting material.
3. It does not depend on temperature and
the strength of applied magnetic field.
4. No magnetic moment is present in the
material.
Paramagnetic Materials
Definition:
Paramagnetic materials become
weakly ionized when placed in a
magnetic field in the same direction as
that of the applied field. It has
permanent dipole moment in each atom.
When external magnetic field is applied,
the induced magnetic moment is
produced which increase the magnetic
induction present in the specimen.
Origin
The orientation of the magnetic
moment along the direction of the
external field gives rise to
paramagnetism. The permanent magnetic
moment arises due to orbital motion of
electron around the nucleus and spin
motion of electron about its own axis.
The magnetic moment due to former
disappears due to the effect of electric
field of the neighbouring charges. But the
magnetic moment due to electron spin
are randomly oriented in the absence of
external field. When the external field is
applied, the magnetic moments tend to
align in the direction of the applied field
resulting in large magnetization. But due
to the thermal agitation of the atoms the
magnetic moments are partially aligned
in the direction of the external field
resulting in weak magnetization.
Characteristics
1. Susceptibility ( m) is positive and
small.
Example For aluminum, ( m ) =
0.065 x10 -6
For Calcium, ( m) = 1.10
x10 -6
The relative permeability μ r > 1.
2. When magnetic field is applied to
paramagnetic material, it is attracted
towards the centre of the material.
3. Susceptibility is inversely proportional
to absolute temperature of the material.
m α (1/T)
Curie’s law for high temperature m = (C/
T)
T = absolute temperature in Kelvin; C =
Curie constant
At low temperature m = C/(T-θ)
θ – paramagnetic curie temperature
θ is always very low. When the
temperature T < curie temperature, the
paramagnetics becomes diamagnetic.
4. Spin alignment: All spins are randomly
oriented.
Ferro Magnetic Materials
Definition:
Ferromagnetic materials are
strongly magnetized in the direction of
the applied magnetic field. It possesses
enormous permanent magnetic moment
in each atom. When external magnetic
field is applied, a large amount of
induced magnetic moment is produced
which increases the magnetic induction
present in the specimen.
Origin
The presence of permanent
magnetic moments in the atoms or
molecules in the specimen gives rise to
ferromagnetism as this magnetic moment
align themselves in the same direction as
that of the external field. The exchange
interaction between unpaired electrons
of adjacent atoms in the crystal lattice
gives rise to local molecular magnetic
field resulting in spontaneous
magnetization.
Characteristics
1. Magnetic susceptibility value is large
and positive. The temperature
dependence of susceptibility for
ferromagnetic materials is said to be
complex.
2. When magnetic field is applied to a
ferromagnetic material, the magnetic
lines of force are strongly attracted by
the specimen.
3. Ferromagnetic materials exhibit
hysteresis. Even if the magnetic field is
removed from the material, it retains the
magnetism due to spontaneous
magnetization. They have permanent
dipole moment.
4. The permeability of a ferromagnetic
material is not a constant, as magnetic
induction (B) does not vary linearly with
magnetic field strength (H).
5. When the temperature of the
ferromagnetic material is greater than its
Curie temperature, then ferromagnetic is
converted into a paramagnetic material.
Antiferromagnetism and Ferrimagnetism:
The only type of magnetic order
which has been considered thus far is
ferromagnetism, in which, in the fully
magnetized state, all the dipoles are
aligned in exactly the same direction.
There are, however, substances which
show different types of magnetic order.
In antiferromagnetic materials such as Cr
and MnO, the dipoles have equal
moments, but adjacent dipoles point in
opposite directions. Thus the moments
balance each other, resulting in a zero
net magnetization.
In ferromagnetic materials (also called
ferrites) such as MnFe 2 O4 , the
magnetic moments of adjacent ions are
antiparallel and of unequal strength. So
there is a finite net magnetization. By
suitable choice of rare-earth ions in the
ferrite lattices it is possible to design
ferromagnetic substances with specific
magnetizations for the use in electronic
components.
Posted by,
Shaiful islam majumder
ME 1/2, Dhaka university of engineering and Technology
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