Magnetism
Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. The most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Only a few substances are ferromagnetic; the most common ones are iron, nickel and cobalt and their alloys. The prefix "" refers to iron, because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, FeO.
Weiss magneton
The idea of elementary magnets originated from the Swiss physicist Walther Ritz, who tried to explain atomic spectra. In 1907 he suggested that atoms might contain chains of magnetized and neutral rods, which were the cause of magnetic properties of materials. Just like elementary charges, this was supposed to give rise to discrete values of the total magnetic moment per atom. In 1909, Weiss performed measurements of the saturation magnetization at the temperature of liquid hydrogen in the laboratory of Heike Kamerlingh Onnes in Leiden. In 1911, Weiss announced that the molar moments of nickel and iron had the ratio of 3:11, from which he derived the value of a magneton.