A) at Curie temperature only
B) at all temperatures
C) below Curie temperature
D) above Curie temperature
Correct Answer: D
Solution :
Iron is a ferromagnetic substance. The Curie point for iron is \[1043\text{ }K\,\text{(}={{770}^{o}}C\text{)}\]. If the temperature of a ferromagnetic material is raised above a certain critical value, called the Curie temperature, the exchange coupling ceases to be effective. Most such materials then become paramagnetic. Also after Curie point, susceptibility of a ferromagnetic substance varies inversely with its absolute temperature. Hence, a ferromagnetic substance obeys Curie-Wiess law -above its Curie temperature.
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