UNIT IV
MAGNETIC AND DIELECTRIC MATERIALS
INTRODUCTION:
Magnetism was observed as early 800 BC in naturally occurring material called lead
stone which was used for navigation purposes. In the modern concept, all materials viz,
metals , semiconductors and insulator are said to exhibit magnetism, though of different
nature. Magnetism arises from the magnetic moment or magnetic dipole of the magnetic
materials. Any material that can be magnetized by application of external magnetic field is
called a magnetic material. When the electrons revolve around the positive nucleus, orbital
magnetic moment arises. Similarly when the electron spins, spin magnetic moment arises.
Magnetic materials are the materials which can be made to behave as magnets. When these
materials are kept in an external magnetic field, they create a permanent magnetic moment in
it.
FUNDAMENTAL TERMS OF MAGNETICS
The important terms involved in the magnetism are as follows.
MAGNETIZATION (M)
When a solid is placed in a magnetic field , it gets magnetized.The magnetic moment per unit
volume developed inside a solid is called Magnetization ,and is denoted by M. It is measured
in amperes per meter (am-1 ).
MAGNETIC INDUCTION OR MAGNETIC FLUX DENSITY(B):
Magnetic induction in any material is the number of lines of magnetic force passing
perpendicularly through unit area. It is also equal to the magnetic force experienced by an
unit north pole placed in that magnetic field.
Unit: weber/m2(or) Tesla
MAGNETIC SUSCEPTIBILITY:
It is a measure of a quality of the magnetic material and is defined as the ratio of the
magnetization (M) produced per unit applied magnetic field.
χ=M/H
Where H is the strength of the applied magnetic field,also referred to as the magnetic field
intensity. χ is a dimensionless quantity.
MAGNETIC FIELD INTENSITY (H):
Magnetic field intensity is the force experienced by unit north pole when placed at the
given point in a magnetic field.
Unit : A/m
MAGNETIC PERMIABILITY(µ)
Magnetic permiability(µ) of any material is the ratio of magnetic induction(B) in
the sample to the applied magnetic field intensity H.
µ=B/H
The ratio µ/ µ0 is called the relative permeability(µr) of the solid.
, µr = µ/ µ0
𝑀
=1+𝜇
𝐻
Where µ0 = permeability of free space (vacuum). It has a value of 4πx 10-7 H/m.
The intensity of magnetization (M) :
The intensity of Magnetization of a sample of a material is the magnetic moment per unit
volume.
I=M/V
2
Unit : weber/m
TYPES OF MAGNETIC MATERIALS
1. Dia-magnetic materials
2. Para-magnetic materials
3. Ferro magnetic materials
4 .Ferri magnetic materials
Dia-magnetic materials:
The diamagnetism is the phenomenon by which the induced magnetic moment is always
in the opposite direction of the applied magnetic field. The materials which exhibit
diamagnetism are called dia-magnetic material.
Properties of diamagnetic materials
When placed inside a magnetic field, magnetic lines of force are repelled.
• Susceptibility is negative and it is independent of temperature.
• There is no permanent dipole moment, so they are called weak magnets.
• When placed inside a magnetic field, magnetic lines of force are repeled.
• Magnetic susceptibility is independent of applied magnetic field strength.
• Relative permeability is slightly less than unity.
Examples: Gold, Germanium, Silicon.
PARA-MAGNETIC MATERIALS:
The paramagnetism is the phenomenon by which the orientations of magnetic
moments are largely dependent on temperature and applied field. The materials which exhibit
paramagnetism are called paramagnetic material.
, Properties of para-magnetic materials:
• They possess permanent magnetic dipoles.
• These dipoles are non-interacting
• The dipoles are randomly oriented and hence in the absence of external applied magnetic
field, the net magnetization in any given direction is zero.
• When placed inside a magnetic field, it attracts the magnetic lines of force.
• Paramagnetic susceptibility is positive and depends greatly on temperature.
Magnetic susceptibility is positive and it is given by
𝐶
𝜒=
𝑇−𝜃
Where
C-curie constant
T-absolute temperature
θ -Curie temperature
• Permeability is greater than one.
Examples: Alkali metals (Na,K), transition metals, Chromium and Yttrium.
Bohr Magneton :
When the atom is placed in a magnetic field, the orbital magnetic moment of the
electrons is quantized. A quantum of magnetic moment of an atomic system is known as Bohr
magneton.
𝑒ℎ
𝜇𝑠 =
4𝜋
Curie Law :
Langevin showed that classical paramagnetic susceptibility (χ) due to the alignment of
magnetic moments along field direction is given by
𝑁𝜇2 𝐶
𝜒 = ℎ0 =
3𝐾𝑇 𝑇
where C = Curie constant and the relation is known as Curie Law.
FERRO MAGNETIC MATERIALS:
Ferromagnetism is a phenomenon by which spontaneous magnetization occurs when T≤θ and
so even in the absence of applied field, the magnetic moments are enormous. Here θ is the
MAGNETIC AND DIELECTRIC MATERIALS
INTRODUCTION:
Magnetism was observed as early 800 BC in naturally occurring material called lead
stone which was used for navigation purposes. In the modern concept, all materials viz,
metals , semiconductors and insulator are said to exhibit magnetism, though of different
nature. Magnetism arises from the magnetic moment or magnetic dipole of the magnetic
materials. Any material that can be magnetized by application of external magnetic field is
called a magnetic material. When the electrons revolve around the positive nucleus, orbital
magnetic moment arises. Similarly when the electron spins, spin magnetic moment arises.
Magnetic materials are the materials which can be made to behave as magnets. When these
materials are kept in an external magnetic field, they create a permanent magnetic moment in
it.
FUNDAMENTAL TERMS OF MAGNETICS
The important terms involved in the magnetism are as follows.
MAGNETIZATION (M)
When a solid is placed in a magnetic field , it gets magnetized.The magnetic moment per unit
volume developed inside a solid is called Magnetization ,and is denoted by M. It is measured
in amperes per meter (am-1 ).
MAGNETIC INDUCTION OR MAGNETIC FLUX DENSITY(B):
Magnetic induction in any material is the number of lines of magnetic force passing
perpendicularly through unit area. It is also equal to the magnetic force experienced by an
unit north pole placed in that magnetic field.
Unit: weber/m2(or) Tesla
MAGNETIC SUSCEPTIBILITY:
It is a measure of a quality of the magnetic material and is defined as the ratio of the
magnetization (M) produced per unit applied magnetic field.
χ=M/H
Where H is the strength of the applied magnetic field,also referred to as the magnetic field
intensity. χ is a dimensionless quantity.
MAGNETIC FIELD INTENSITY (H):
Magnetic field intensity is the force experienced by unit north pole when placed at the
given point in a magnetic field.
Unit : A/m
MAGNETIC PERMIABILITY(µ)
Magnetic permiability(µ) of any material is the ratio of magnetic induction(B) in
the sample to the applied magnetic field intensity H.
µ=B/H
The ratio µ/ µ0 is called the relative permeability(µr) of the solid.
, µr = µ/ µ0
𝑀
=1+𝜇
𝐻
Where µ0 = permeability of free space (vacuum). It has a value of 4πx 10-7 H/m.
The intensity of magnetization (M) :
The intensity of Magnetization of a sample of a material is the magnetic moment per unit
volume.
I=M/V
2
Unit : weber/m
TYPES OF MAGNETIC MATERIALS
1. Dia-magnetic materials
2. Para-magnetic materials
3. Ferro magnetic materials
4 .Ferri magnetic materials
Dia-magnetic materials:
The diamagnetism is the phenomenon by which the induced magnetic moment is always
in the opposite direction of the applied magnetic field. The materials which exhibit
diamagnetism are called dia-magnetic material.
Properties of diamagnetic materials
When placed inside a magnetic field, magnetic lines of force are repelled.
• Susceptibility is negative and it is independent of temperature.
• There is no permanent dipole moment, so they are called weak magnets.
• When placed inside a magnetic field, magnetic lines of force are repeled.
• Magnetic susceptibility is independent of applied magnetic field strength.
• Relative permeability is slightly less than unity.
Examples: Gold, Germanium, Silicon.
PARA-MAGNETIC MATERIALS:
The paramagnetism is the phenomenon by which the orientations of magnetic
moments are largely dependent on temperature and applied field. The materials which exhibit
paramagnetism are called paramagnetic material.
, Properties of para-magnetic materials:
• They possess permanent magnetic dipoles.
• These dipoles are non-interacting
• The dipoles are randomly oriented and hence in the absence of external applied magnetic
field, the net magnetization in any given direction is zero.
• When placed inside a magnetic field, it attracts the magnetic lines of force.
• Paramagnetic susceptibility is positive and depends greatly on temperature.
Magnetic susceptibility is positive and it is given by
𝐶
𝜒=
𝑇−𝜃
Where
C-curie constant
T-absolute temperature
θ -Curie temperature
• Permeability is greater than one.
Examples: Alkali metals (Na,K), transition metals, Chromium and Yttrium.
Bohr Magneton :
When the atom is placed in a magnetic field, the orbital magnetic moment of the
electrons is quantized. A quantum of magnetic moment of an atomic system is known as Bohr
magneton.
𝑒ℎ
𝜇𝑠 =
4𝜋
Curie Law :
Langevin showed that classical paramagnetic susceptibility (χ) due to the alignment of
magnetic moments along field direction is given by
𝑁𝜇2 𝐶
𝜒 = ℎ0 =
3𝐾𝑇 𝑇
where C = Curie constant and the relation is known as Curie Law.
FERRO MAGNETIC MATERIALS:
Ferromagnetism is a phenomenon by which spontaneous magnetization occurs when T≤θ and
so even in the absence of applied field, the magnetic moments are enormous. Here θ is the
