FERROMAGNETISM
a) The term Ferromagnetism was coined by Curie Pierre in 1895 .
b) Those substances which when placed in a magnetic field, are strongly magnetised in the direction of the applied field are called as Ferromagnetic substances.
c) A Ferromagnetic substance when placed in a non-uniform magnetic field, show a very strong tendency to move from the weaker to the stronger parts of the magnetic field.
d) Ferromagnetic materials are made up of atoms with permanent dipole moments.
e) Ferromagnetic substances retain their magnetism even when the external magnetic field is removed. This tendency of Ferromagnetic substances to remember their magnetic history is called as " Hysteresis " .
f) Due to their this property Ferromagnetic substances can be converted into Permanant Magnets.
g) Being Permanant magnets the Ferromagnetic substances can give rise to a magnetic field even in the absence of an external magnetic field.
h) Ferromagnetic substances have very high Magnetic Susceptibilities, ranging from 1000 to 1,00,000 .
i) The Relative Permeability of the Ferromagnetic substances is much more greater than 1 and hence for a Ferromagnetic substance the magnetic lines of force are strongly attracted.
j) When a Ferromagnetic substance is heated above a certain temperature it loses it's ferromagnetism and become Paramagnetic.
k) The temperature at which a Ferromagnetic substance becomes Paramagnetic is called as Curie Temperature.
l) Ferromagnetism is exhibited by solid materials only.
Elements from the Periodic Table which exhibit Ferromagnetism are :-
1) Iron
2)
Cobalt
3)
Nickel
4)
Gadolinium
Anti-Ferromagnetism
a) Antiferromagnetism was first discovered by Neel and Bitter and later extended by Van Vleck.
b) In the presence of a strong magnetic field, Antiferromagnetic materials are weakly magnetised in the direction of the applied field.
c) In Antiferromagnetic materials, the magnetic moments are aligned in opposite directions and are equal in magnitude.
d) Due to this the magnetic moments of the neighbouring atoms cancel each other and its net magnetisation is zero.
e) Antiferromagnetism occur commonly among transition metal compounds, especially oxides.
f) Antiferromagnetism generaly exist at low temperatures and vanishes at and above a certain temperature called the Neel temperature .
g) Above the Neel temperature, the Antiferromagnetic material is typically paramagnetic .
h) Chromium is an example of element which exhibit Antiferromagnetism.
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