Question

What is the difference between paramagnetic and diamagnetic substances?

Hint:

Compare the sign of susceptibility and whether the atoms carry a permanent magnetic moment.

Answer 1

Step 1: Paramagnetic substances.
These are substances that are weakly attracted by a magnet. When placed in an external magnetic field, they get feebly magnetised in the same direction as the field, so their relative permeability is slightly greater than 1 and their magnetic susceptibility \( \chi \) is small and positive \( (\chi > 0) \). Their atoms have a net (permanent) magnetic moment. Example: aluminium, platinum, oxygen.

Step 2: Diamagnetic substances.
These are substances that are weakly repelled by a magnet. In an external field they get feebly magnetised in the opposite direction to the field, so their relative permeability is slightly less than 1 and their susceptibility is small and negative \( (\chi < 0) \). Their atoms have no net magnetic moment. Example: bismuth, copper, water.

\[\boxed{\text{Para: weak attraction, } \chi > 0;\ \ \text{Dia: weak repulsion, } \chi < 0}\]