Guillaume 6 explains the ferromagnetism of Heusler's alloy by supposing that the naturally low critical temperature of the manganese contained in it is greatly raised by the admixture of another appropriate metal, such as aluminium or tin; thus the alloy as a whole becomes magnetizable at the ordinary temperature.
Diamagnetism, in short, is an atomic phenomenon; paramagnetism and ferromagnetism are molecular phenomena.
Ferromagnetism was explained by Ampere on the hypothesis that the magnetization of the molecule is due to an electric current constantly circulating within it.
How would you define ferromagnetism? Add your definition here.