BSc 6th sem Physics 1 magnetic properties of matter and dielectrics
By. Dr. K S Suresh
VI Semester B.Sc. Physics Unit – II : Magnetic Properties of Matter
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Review of basic formulae :
Magnetic intensity, magnetic induction, permeability, magnetic susceptibility, magnetization (M), Classification of Dia , Para, and ferro– magnetic materials. Classical Langevin Theory of dia , – and Paramagnetic Domains. Quantum Mechanical Treatment of Para magnetism. Curie’s law, Weiss’s Theory of Ferromagnetism and Ferromagnetic Domains. Discussion of B-H Curve. Hysteresis and Energy Loss, Hard and Soft magnetic materials
Introduction : Matter is made of atoms which contain charged particles called electrons
revolving round the nucleus. These moving electrons produce magnetic field. Also, a
current carrying conductor produces magnetic field. All materials are affected in some
way or the other by a magnetic field. However, not all materials react the same way.
A magnetic material is a material which can attract or repel other substances under
the influence of its magnetic field. The action of attracting or repelling a substance
depend on the alignment of atomic magnetic moments in the substance in the presence
of external magnetic field.
Magnetic Field: It is a region around a magnet where other magnetic
materials experience a force. Magnetic field can be described by
imaginary lines of force around a magnet which enables other
magnetic materials to get repelled or attracted towards it.
Properties of Magnetic field Lines
➢ The Magnetic field lines enter the south pole and comes out of the north pole
forming closed loops.
➢ The magnetic field lines are strong near the poles of the magnet.
➢ There is no chance of magnetic field lines intersecting each other.
➢ More the closeness of the magnetic field lines, more is the strength of magnetic
field.
1. Magnetic permeability
When a magnetic material is placed in a magnetizing field
H (dia. a), the material acquires magnetism due to
induction. The lines of force of the magnetizing field
concentrate inside the material .
Magnetic Flux Density (B) : When a substance is subjected to the magnetic field H,
then the number of magnetic field lines that pass through the substance per square
meter is known as Magnetic Flux Density or magnetic induction.
Classification of magnetic materials Depending on the way the magnetic moments of
the electrons in the atoms of a material react to an applied magnetic field, materials can
be classified as diamagnetic, paramagnetic and ferromagnetic materials.
Diamagnetic material : Those substances which are weakly magnetized in a direction
opposite to the applied magnetic field are called diamagnetic substances.
Examples: Gold, silver lead, copper, antimony, bismuth, silicon, mercury, water, air,
hydrogen, nitrogen etc..
Explanation : In general, the magnetic moments of atoms are oriented such that the
vector sum of the magnetic moments of atoms is zero. When such a diamagnetic
substance is placed in an external magnetic field, the substance as a whole acquires a
net magnetic moment in a direction opposite to the applied field. Atoms of diamagnetic
materials do not possess any unpaired electrons.
Characteristics :
1. They possess small and negative
susceptibility.
2. The Magnetic moment of the atoms align
in the opposite direction to applied
magnetic field.
3. They are slightly repelled by a magnetic
field.
4. When placed in a non-uniform magnetic field, they tend to move from the stronger
to the weaker part of the field.
5. They do not retain the magnetic properties when the external field is removed.
6. Susceptibility is independent of temperature of the material.
Paramagnetic materials : Those substances which are weakly magnetized in the same
direction as the applied magnetic field are called paramagnetic substances.
Examples : Aluminum, platinum, manganese, chromium, sodium, calcium, lithium,
tungsten, niobium, oxygen etc..
Etc....
