40. Curie Temperature

A nickel paper clip (a regular steel one is available too) attached to a base with a string is suspended in air by the use of a magnet. If the nickel paper clip is heated with a lighter (for the steel paper clip a blowtorch is required) beyond a certain temperature called the Curie temperatures it is no longer attracted by the magnet.

The Curie temperature (Tc) is the critical temperature beyond which a previously ferromagnetic material becomes paramagnetic. On the atomic level, below the Curie temperature the magnetic moments, contributed mainly by the electrons, are aligned in their respective domains and even a weak external field results in a net magnetization. As the temperature increases to Tc and above however, fluctuations due to the increase in thermal energy destroy that alignment. Tc for nickel is 631K, while that for iron is 1043K.