Question

Iron is a ferromagnetic in
A. at all temperatures
B. at NTP only
C. above $770{}^\circ C$
D. Below $770{}^\circ C$

Answer 1

Hint: Ferromagnetism is the certain mechanism by which some of the materials become permanent magnets, or they are attracted to magnets. In physics, so many different types of magnetism are distinguished. Ferromagnetism is one of them. Iron is a ferromagnetic material.

Complete step-by-step answer:
First of all let us take a look at what a Curie temperature means. Above the Curie temperature some certain materials will completely lose their magnetic properties permanently and hence they will be replaced by the induced magnetism. Above the Curie point which is also known as the Curie temperature the spontaneous magnetization of the ferromagnetic material vanishes and it will become paramagnetic which means the magnetism becomes very weak. This happens due to the thermal energy required to overcome the internal aligning forces of the substances. As we are heating a magnet we supply it with greater thermal energy, so the electron spins which are similar to tiny magnets themselves will become more similar to be in high-energy states, pointing oppositely to their neighbours. This means that they’re lined up very less therefore the total magnetism is being reduced. For iron, the Curie temperature is given as $770{}^\circ C$.
Above this, the magnetic property will be lost. So the correct answer is option D.

Note: Curie point which is also known as Curie temperature, is the temperature at which some specific magnetic materials will undergo a clear change in their magnetic properties. In the case of rocks and minerals, the magnetism of remnant materials seemed to be below the Curie point that means about $570{}^\circ C$ for the common magnetic mineral magnetite.