PGTRB:PHYSICS : PROPERTIES OF MAGNETISM. - Tamil Crowd (Health Care)

PGTRB:PHYSICS : PROPERTIES OF MAGNETISM.

 PGTRB:PHYSICS : PROPERTIES OF MAGNETISM.

Properties of diamagnetic materials:

  • For diamagnetic substance relative permeability is slightly less than unity.
  • The susceptibility of a diamagnetic material has a low negative value. 
  • It is independent of temperature.
  • In an external magnetic field, they get magnetised in a direction opposite to the field and so they have a tendency to move away from the field.
  • If suspended freely, they set themselves they set themselves perpendicular to the field.
  • Example: Sb, Bi, Zn, Ag, Au, Pb etc., 

Properties of paramagnetic materials:

  • These substances have relative permeability is >1 and susceptibility positive.
  • The susceptibility decreases with rise temperature.
  • In an external magnetic field, these substances get magnetised in the direction of the filed. Hence they move from weaker to stronger part of the external field.
  • If suspended freely, they set themselves parallel to the field.
  • Example :platinum, aluminium, chromium, manganese, copper sulphate, liquid oxygen and solutions of salts of iron and nickel.

Properties of ferromagnetic materials:

  • The values of permeability and susceptibility of these materials are very large.
  • They get strongly magnetised in the direction of the external field and so they are strongly attracted by magnets.
  • They set themselves parallel to the external field of suspended freely.
  • These materials exhibited the phenomenon of hysteresis.
  • As temperature increases, the value of susceptibility decreases.
  • Above certain temperature, known as Curie temperature, ferromagnetics become paramagnetics.
  • Example: Iron, nickel and cobalt.

Properties of Antiferromagnetism:

  • The only type of magnetic order which has been considered thus far is ferromagnetism, in which, in the fully magnetised state, all the dipoles are aligned in exactly the same direction.
  • The substances which show different types of magnetic order.
  • In antiferromagnetic materials such as Cr and Mno, the dipoles have equal moments, but adjacent dipoles point in opposite directions. 
  • Thus the moments balance each other resulting in a zero net magnetisation.
  • The gross magnetic effects of such materials are very small.
  • When heated above critical temperature, called the Neel temperature, the exchange interaction cases and these materials become paramagnetic.

Properties of ferrimagnetic:

  • In ferrimagnetic materials also called ferrites.
  • Example: MnFe2O4.
  • The magnetic moments of adjacent ions are antiparallel and of unequal strength. 
  • There is a finite net magnetisation.
  • Anet magnetism, which lies in between ferromagnetism nd antiferromagnetism.
  • Here again, when the temperature is above a critical value, the material becomes paramagnetic.
  • By suitable choice, of rare-earth ions in the ferrite lattices it is possible to design ferrimagnetic substances with specific magnetizations for use in electronic components. 
  • Ferrites are good insulators and have very small eddy current losses when subjected to very high fields. 
  • Ferrites are often used in microwave systems.

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