1. General features and properties

The word "magnet" owes its origin to the Latin "adamas", meaning iron, diamond. Indeed, the first known magnets, as far back as the time of the Greeks, were iron-based; these were magnet stones, which contained magnetite, a natural iron oxide (chemical formula Fe ₃ O ₄ ). Around the 12th century, the first artificial iron magnets appeared in Europe, and little progress was made in this field until the 1930s. The materials used then were martensitic hard chromium, tungsten and cobalt steels, characterized by the traditional U-shape.

Technological advances over the last seventy years have completely revolutionized the possibilities of permanent magnets. New materials have been discovered, synthesized and industrialized, with performances such...