A ferromagnet is a material that displays strong magnetic properties in the presence of an external magnetic field. In general, ferromagnets are materials that contain iron, cobalt, or nickel. However, other elements can also exhibit ferromagnetic behavior, such as gadolinium and dysprosium. Ferromagnets display a unique form of magnetism known as spontaneous magnetization: when placed in a magnetic field, they spontaneously align their atomic dipoles with the applied field (Figure 1). This property is what gives rise to the strong magnets found in many applications today.
Ferromagnetic materials have been known since antiquity; lodestones were used for navigation long before the discovery of electricity. The modern understanding of magnetism began with the work of English physicist William Gilbert in 1600. Gilbert showed that Earth itself is a giant magnet, with north and south poles just like those of smaller magnets. He also demonstrated that many materials could be made into magnets by stroking them with lodestones—a process now known as induction.
The first scientific explanation for why some materials are attracted to others was proposed by French physicist Charles Augustin de Coulomb in 1785. Coulomb’s theory correctly predicted the strength of the force between two masses at different distances apart—but it did not explain why some substances are more likely to be affected by this force than others. This mystery remained unsolved until 1820, when Danish physicist Hans Christian Oersted discovered that electric currents generate magnetic fields. Oersted’s finding led directly to the development of electromagnets—and ultimately to countless technological innovations based on this principle (Figure 2).
It wasn’t until 1845 that English scientist Michael Faraday finally explained how certain substances become magnets in the first place. Faraday showed that when an electric current flows through a coil of wire wrapped around an iron core, it generates a magnetic field (Figure 3). This phenomenon is now known as electromagnetic induction, and it forms the basis for technologies like electric motors and generators—as well as for our understanding of how ferromagnets work.