Ferromagnetism

Ferromagnetic materials exhibit spontaneous magnetization in the absence of a magnetic field but can also be permanently magnetized by an external field. In ferromagnetic material the magnetic moments resulting from the electrons rotating round the atoms must be orientated such that a significant proportion contribute to the net magnetization of the material. Some of the more common inorganic ferromagnetic materials are, iron, cobalt, nickel, mixed oxides of these metals, together with mixtures of bismuth and manganese, arsenic and manganese and chromium oxide. The magnetic properties change with temperature and there is a temperature (the Curie temperature) where the material ceases to exhibit spontaneous magnetization and becomes paramagnetic.