CLASSIFICATION OF MAGNETIC MATERIALS.
Iron and steel are not the only substances , which are attached by a magnet or which can be magnetised . In fact, all the substances possess magnetic properties On the basis of their magnetic behaviour, Faraday divided the magnetic materials into three classes:
Those substances, which when placed in a magnetic field are feebly magnetised in a direction opposite to that of the magnetising field , are called diamagnetic substances
When a diamagnetic substances is placed inside an external magnetic field, the magnetic field inside the diamagnetic is found to be slightly less than the external magnetic field It is observed that when a diamagnetic sample is placed inside a non – uniform magnetic field it tends to move from stronger part to the weaker part of the magnetic field. It may be pointed out that the diamagnetic effects are too feeble to be detected, unless the applied magnetic field is strong. The behavior of a diamagnetic substance is independent of temperature. Further, a diamagnetic substance has the nature similar to that of a dielectric having non- polar atoms. A few examples of diamagnetic substances are copper, zinc , bismuth , silver , gold, lead, glass, marble, water , helium , argon , sodium chloride.
Those substances, which when placed in a magnetic field , are feebly magnetised in the direction of the magnetising field, are called paramagnetic substances .
When a paramagnetic substance is placed inside an external magnetic field, the magnetic field inside the paramagnetic is found to be a slightly greater than the external magnetic field. In contrast to the behavior of diamagnetic, a paramagnetic substance tends to move from weaker part of the magnetic field to stronger part, when placed in a non- uniform magnetic field. Further, in contrast to diamagnetic, the behavior of a paramagnetic is temperature dependent. Also, the paramagnetic effects are perceptible only with a strong magnetic field. The nature of a paramagnetic is similar to that of a dielectric having polar atoms . A few examples of paramagnetic substances are aluminum sodium, antimony , platinum, copper chloride, manganese, chromium , liquid oxygen ,etc .
Those substances, which when placed in a magnetic field are strongly magnetised in the direction of the magnetising field, are called ferromagnetic.
When a ferromagnetic substance is placed inside the ferromagnetic substance gets greatly enhanced . As a result , when a ferromagnetic is placed in a non -uniform magnetic field, it quickly moves from weaker part to stronger part of the magnetic field . In other words , the ferromagnetic effects are perceptible even in the presence of a weak magnetic field. Further, the ferromagnetic behavior of a substance becomes temperature dependent above certain temperature, which is characteristic of that substance. It is called Curie temperature . The nature of a ferromagnetic may be compared to that of a ferromagnetic type dielectric . A few examples of ferromagnetic materials are iron, nickel, cobalt, alnico, etc.
The nature of diamagnetic, paramagnetic and ferromagnetic substances can be successfully explained on the basis of electron- theory of magnetism, which makes use of the fact that an atom may possess magnetic moment due to obtain and spin motion of the electron in the atom.
CLASSIFICATION OF MAGNETIC MATERIALS.
DIAMAGNETISM THE BASIS OF ELECTRON THEORY.
As we know that in an atom , electrons resolve in circular orbis and as such they behave as tiny current loops and possess magnetic dipole moments. THE magnetic dipole moment of an electron revolving with velocity V in an orbit of radius r is given by
M = evr/ 2 ,
Where e is magnitude of charge on the electron . Now , angular momentum of electron is given by
L = m(e) v r,
Where m is mass of electron .
V = L/m
From the above equations,
M = eL/2m
In a diamagnetic material , there are no unpaired electrons . Further , the two electrons of a pair possess orbital motion in opposite directions .