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
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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.
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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.
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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 moment 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.
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The orientation of the magnetic moment along the
direction of the external field gives rise to para-magnetism.
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
neighboring 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.
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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.
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E.g: Cadmium,
Copper, Silver, Bismuth, Tin, zinc, Gold, Niobium and its compounds.
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Eg: Aluminum, Calcium, Oxygen, Platinum, Titanium
and Chromium.
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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
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