Magnetic materials

Abstract

We saw in the previous chapter that magnetic fields are produced in a vacuum by currents in conductors. In this chapter, we will consider magnetic effects associated with matter. All materials have spin and orbital motion of charges at the atomic scale. For most materials, the random orientations of these internal currents tend to cancel out significant magnetic effects. However, in certain magnetic materials, such as iron or permanent magnets, these internal currents do not cancel, and there is a net external effect that also produces or enhances magnetic fields. In the field theory we have been discussing, the magnetic field B must be a continuous function of position. Thus, in magnetic materials, the macroscopic field B must be an average of the rapidly varying local fields surrounding the atoms in the material. [1]