Monday, June 3

Paramagnetism and Diamagnetism

Introduction to Paramagnetism and Diamagnetism:

1. Diamagnetic substances are those which have tendency to move from stronger to the weaker part of the extended magnetic field.  In other words, unlike the way a magnet attracts metals like iron, it would repel a diamagnetic substance.

2. Paramagnetic substances are those which get weakly magnetized when placed in an external magnetic field.  They have tendency to move from a region to weak magnetic field to strong magnetic field i.e. they get weakly attracted to a magnate.

Diamagnetism: paramagnetism and diamagnetism

Diamagnetism: The simplest explanation for diamagnetism is as follows:

(a)Electron in an atom orbiting around nucleus possess orbital angular momentum.  These orbiting electrons are equivalent to current carrying loop and thus possess orbital magnetic movement.

(b)Diamagnetic substances are those ones in which resultant magnetic movement in a atom is zero.  When magnetic field is applied those electrons having orbital magnetic movement in the same directions slow down and those in the oppo0site direction speed up.  This happens due to induced current in accordance with the lenz’s law.

(c)Some diamagnetic materials are bismuth, copper, lead, silicon, nitrogen, water and sodium chloride.

(d)Diamagnetism is present in all the substances.  However, the effect is so weak in most cases that it gets shifted by other effects like paramagnetism, ferromagnetism etc.

(e)The most exotic diamagnetic material are super conductors.  These are metals, cool to very low temperatures which exhibits both perfect conductivity and perfect diamagnetism.  A superconductor repels a magnet and is repelled by the magnet.

Paramagnetism: paramagnetism and diamagnetism


(a)The individual atoms of a paramagnetic material posses a permanent magnetic dipole movement of their own.  On account of the ceaseless random thermal motion of the atoms, no net magnetization is seen.

(b)In the presence of external field, which is strong enough, and at low temperature, the individual atomic dipole movement can be made to align and point in the same direction as the external field.

(c)Some paramagnetic materials are aluminium, sodium, calcium, oxygen and copper chloride. Experimentally, one finds that the magnetization of a paramagnetic material is inversely proportional to the absolute temperature T.

M = CB0/T

This is known as Curie’s law.

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