Diamagnetism
a)
The term Diamagnetism was coined by Michael Faraday in 1845 .
b) Those substances which when placed in a magnetic field, are weekly magnetised in a direction opposite to that of the magnetising field are called as Diamagnetic Substances .
c) When a Diamagnetic substance is placed in a non-uniform magnetic field , it's atoms acquire a small magnetic dipole moment in a direction opposite to that of the magnetic field .
d) As a result , the Diamagnetic substances moves from stronger part of the magnetic field to it's weaker part i.e. they are weakly repelled by the magnet .
e) The Diamagnetic substances do not retain their magnetic properties when the external magnetic field is removed.
f) Diamagnetism is usually observed in Solids composed of atoms with completely filled electronic shells .
g) The reason is that in a completely filled shell there are equal number of electrons with positive and negative spins, so that the total magnetic moment is zero .
h) This is the reason why the individual atoms in a Diamagnetic substance do not posses any net magnetic dipole moment.
i) The magnetic susceptibility of a Diamagnetic substance has a small negative value.
j) The relative permeability of a Diamagnetic substance is slightly less than 1.
k) The behaviour of a Diamagnetic substance is independent of temperature.
l) That is why Magnetic susceptibility of Diamagnetic substances do not change with temperature and hence the Diamagnetic substances do not obey Curie's Law .
m) The Diamagnetic substances when placed in a uniform magnetic field, they set their longest axis at right angles to the direction of the field and the shortest axis along the direction of the field.
n) Orbital motion of electrons is the root cause of magnetism in Diamagnetic substances.
o) All Substances are Diamagnetic to some extent .
Elements from the Periodic Table which exhibit Diamagnetism are :-
1)
Hydrogen
2)
Helium
3)
Beryllium
4)
Boron
5)
Carbon
6)
Nitrogen
7)
Neon
8)
Silicon
9)
Phosphorus
10)
Sulphur
11)
Chlorine
12)
Argon
13)
Copper
14)
Zinc
15)
Gallium
16)
Germanium
17)
Arsenic
18)
Selenium
19)
Bromine
20)
Krypton
21)
Silver
22)
Cadmium
23)
Indium
24)
Antimony
25)
Tellurium
26)
Xenon
27)
Gold
28)
Mercury
29)
Thallium
30)
Lead
31)
Bismuth
Of this all elements Bismuth and carbon graphite are the strongest Diamagnetic materials.
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