Q.What happens to a ferromagnetic substance heated above Curie temperature?

Above the Curie temperature, thermal agitation destroys the domain alignment responsible for ferromagnetism.

A ferromagnetic substance owes its strong magnetism to spontaneously aligned magnetic domains. As temperature rises, thermal (random) agitation of atoms increases, progressively disrupting this alignment. At a certain critical temperature — the Curie temperature — the domain structure breaks down completely, and above this temperature, the substance loses its ferromagnetic property and behaves as an ordinary * …