Summary

In this module, we have learnt the basics of magnetism where we saw that while diamagnetism is inherently present in all materials, the contribution is masked by paramagnetism or ferromagnetism in some materials. Diamagnetism in most materials is characterized by small but negative magnetic susceptibility while paramagnetic materials exhibit small and positive susceptibilities. In contrast ferro- and ferrimagnetic materials show large and positive susceptibilities representing a strong magnetic response of the materials. While most ferromagnetic materials happen to be metals or alloys, many spinel structured oxide ceramics, especially those containing iron and other magnetic elements, e.g. Fe₃O₄ tend to be ferrimagentic. However, there are other oxide ceramics such as hexagonal ferrites and garnet structured oxides which also show reasonably large magnetic moments. These ferrites are useful for a variety of applications including electromagnets, shields, data storage devices and microwave applications.