ABSTRACT
The word “magnet” has its origin in a magnetic material known as magnetite, which is a form of iron oxide or lodestone used as a magnetic compass Lodestone was mined in the province of Magnesia It is believed that among the minerals found in Magnesia (a part of Macedonia), magnesium carbonate was white, manganese dioxide was brown, and the third-magnetite-was black iron oxide The latter was probably the first material known to be magnetic
As we will see, in reality, all materials in this world are magnetic, that is, they respond to magnetic fields in some fashion One objective of this chapter is to introduce the fundamental concepts related to magnetic materials In this regard, we will explore the origin of magnetism in materials We will define different types of magnetism in materials that include ferromagnetic and ferrimagnetic materials The second objective is to explore different technologies based on the use of magnetic materials, including magnetic materials used in information storage (eg, magnetic hard disks) We will also briefly mention materials called multiferroics These materials simultaneously exhibit two or more switchable properties, such as ferroelectric and ferromagnetic behaviors
Most concepts regarding magnetic materials and technologies would be better followed if you have already learned the basics of linear dielectric materials and ferroelectric materials from Chapter 8 You would start to recognize that many of the equations we would deal with here for magnetic materials are very similar to those used for ferroelectrics Thus, the so-called phenomenology underlying the group of dielectrics and ferroelectrics and that of ferromagnetic and ferrimagnetic materials is similar However, it is important to keep in mind that although many of the phenomena and equations appear very similar, the physical origins of magnetic and dielectric behavior are quite different.
