Curie Temperature:
The Curie temperature (Tc) is the temperature at which a material undergoes a phase transition from a ferromagnetic or anti-ferromagnetic phase to a paramagnetic phase. It is named after Pierre Curie, the physicist who discovered this behavior.

Phase Transition:
A phase transition refers to a change in the physical properties of a material, such as its magnetic behavior, as the temperature is varied. In the context of magnetism, a phase transition occurs when the alignment of magnetic moments in a material changes.

Anti-ferromagnetic Phase:
In an anti-ferromagnetic material, neighboring magnetic moments align in a way that cancels out their overall magnetization. This results in a net zero magnetization for the material.

Paramagnetic Phase:
In a paramagnetic material, the magnetic moments of individual atoms or molecules are randomly oriented, resulting in no net magnetization.

Temperature and Phase Transition:
The temperature at which a phase transition occurs is determined by the balance between the thermal energy and the energy associated with the magnetic interactions in the material.

When the temperature is high, the thermal energy dominates, and the material is in a paramagnetic phase.

As the temperature decreases, the energy associated with the magnetic interactions becomes more significant. At the Curie temperature, this energy overcomes the thermal energy, and a phase transition from the anti-ferromagnetic phase to the paramagnetic phase occurs.

Choice B: Curie temperature:
Therefore, the correct answer is option B – Curie temperature. It is the temperature at which a change from the anti-ferromagnetic phase to the paramagnetic phase occurs.