Atom Magnetism: Ferrite Circulators—Past, Present, and Future

Magnetism, at the very fundamental level, is attributed to the circular motion of elementary charges. This occurs when electrons spin around their own axes or when they rotate around the nucleus of an atom. The combination of these two types of motion gives an atom its magnetic moment [1]. The three most significant elements from the point of view of magnetism are iron, nickel, and cobalt. Their atoms possess a large magnetic moment due to a large number of unpaired electrons in their outermost shell. They also naturally assume a crystal structure with all atoms aligned with their magnetic moments in the same direction, a configuration referred to as "ferromagnetism" [2].