From: Department of Physics and Astronomy University of Delaware

The study and applications of magnetic materials date back to ancient China, Greece, and the dawn of modern science when in 1600 William Gilbert published his great study of magnetism De Magnete which gave the first rational explanation to the mysterious ability of the compass needle to point north-south. Around the same time, Decartes formulated mechanical model to explain magnetism. The XX century models of magnetic materials have influenced greatly the development of quantum mechanics, statistical mechanics, metalurgy, and biology. The ferromagnets are typically classified as:

• hard(or permanent), with coercivity (applied magnetic field to bring their magnetization to zero) usually above 0.25 T which makes them useful in electromotors, car starters, alternators for wind power generation, computer hard drives, loudspeakers, locks, and microphones.
• soft with coercivities below 1 mT which finds applications in transformer cores, high frequency and microwave applications, and recording heads.

Depending on their electronic structure, itinerant magnets involving delocalized electrons are classified as: iron-series transition metals and their allows; rare-earth magnets; alloys containing heavy transition metals; metallic oxides, and recently pursued diluted magnetic semiconductors.