Question

What is the difference between paramagnetic and diamagnetic materials?

Hint:

Compare their behaviour in a magnetic field and the sign of their susceptibility \(\chi\).

Answer 1

Step 1: Define paramagnetic materials.
Paramagnetic materials are substances that are weakly attracted towards a strong external magnetic field. Their atoms have a permanent (net) magnetic dipole moment because of unpaired electrons. Examples: aluminium, platinum, sodium.

Step 2: Define diamagnetic materials.
Diamagnetic materials are substances that are weakly repelled by an external magnetic field. Their atoms have no net magnetic dipole moment (all electron spins are paired). Examples: bismuth, copper, water.

Step 3: Compare their key properties.
1. Behaviour in a field: paramagnetic are feebly attracted; diamagnetic are feebly repelled.
2. Magnetic dipole moment: paramagnetic atoms have a permanent moment; diamagnetic atoms have zero net moment.
3. Relative permeability \(\mu_{r}\): paramagnetic have \(\mu_{r}\) slightly greater than 1; diamagnetic have \(\mu_{r}\) slightly less than 1.
4. Magnetic susceptibility \(\chi\): paramagnetic have a small positive \(\chi\); diamagnetic have a small negative \(\chi\).
5. In a non-uniform field: paramagnetic move from weaker to stronger region; diamagnetic move from stronger to weaker region.

Result: Paramagnetic substances are weakly attracted with small positive susceptibility, while diamagnetic substances are weakly repelled with small negative susceptibility.