Q.18 What is Curie temperature? Distinguish between diamagnetic and paramagnetic substances.
Best answer
Answer:
Curie temperature: The temperature above which a ferromagnetic substance loses its ferromagnetism and becomes paramagnetic is called the Curie temperature \(T_C\) (e.g. about 1043 K for iron).
| Diamagnetic substances | Paramagnetic substances |
|---|---|
| 1. Atoms have no net (permanent) magnetic moment; the orbital and spin moments cancel. | 1. Atoms have a net permanent magnetic moment. |
| 2. Weakly repelled by a magnet; tend to move from stronger to weaker parts of a field. | 2. Weakly attracted by a magnet; tend to move from weaker to stronger parts of a field. |
| 3. Susceptibility is small and negative; relative permeability is slightly less than 1. | 3. Susceptibility is small and positive; relative permeability is slightly greater than 1. |
| 4. Susceptibility is practically independent of temperature. | 4. Susceptibility is inversely proportional to absolute temperature (Curie’s law, \(\chi = C/T\)). |
| 5. Examples: bismuth, copper, water, gold. | 5. Examples: aluminium, platinum, sodium, oxygen. |
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