Curie temperature

The Curie point is the temperature above which a ferromagnetic material, such as iron or nickel and their alloys, loses its ferromagnetic properties. The Curie temperature for nickel is 385°C and for iron is ~700°C. The curie transition is rather like a phase change. The material can be cycled indefinitely.

One immediate consequence of the Curie temperature is the non ferromagnetic nature of the core of the Earth, largely made of iron, but not a permanent magnet because it is well above the critical temperature.

The coins shown, (from India, Europe and China) are ferromagnetic. It would be interesting to find their approximate Curie temperatures.