Magnets are one of the most fascinating materials. Children use them as toys and their parents use them to fasten images of their cute faces on to refrigerators. However, magnetic materials also find all kinds of important roles in technology. Magnets based on the traditional metals (iron, nickel, and manganese) have been used for transformers and motors. These magnets have high conductivities and, as a result, carry large (unwanted) Eddy currents at high frequencies. With advances in ceramic magnets (containing iron or other magnetic elements) the applications of magnetic materials has greatly expanded. Ceramic magnets have become important in numerous information processing technologies, although their most dominant impact has been on information storage. Also, propagation of electromagnetic waves in magnetic materials allows for a variety of interesting devices that find use in microwave technology. In recent years, traditional semiconductors, such as GaAs, have been doped with Mn to create magnetic semiconductors. There have been suggestions that devices based on electron spin in such materials can lead to a new field of spintronics with applications in high-performance information processing. However, spintronics has not yet made any impact on technology, primarily because of the very low temperatures needed for such devices to operate.
In this chapter we will first examine some basic physics of magnetic materials and the interaction of electrons with magnetic fields. We will then examine how magnetic materials can be exploited for device applications.
The magnetic properties of a material are described through the magnetization M (magnetic moment per volume).