Magnets have been used in society for centuries. In ancient times they were considered paranormal or mysterious substances. Nobody knew how or why the magnets attracted certain but not all materials. As we have seen in Chapter 1, it was not until the seventeenth century that there was considerable understanding of electromagnetism and a progressive increase in the use of magnetic materials as useful functional materials. Nowadays magnets are all-pervasive in modern society, starting from home to medical applications, to transport, and industrial sectors (Fig. 2.1).

We utilize magnetism all over our homes although it may not be very obvious. Electric motors create force by using electricity and magnetic fields. So nearly all household appliances such as fans, washing machines, vacuum cleaners, and blenders that use electricity to create motion invariably have magnets. Many households have small magnets holding paper notes or small items to the metal refrigerator door. While some magnets are visible, the others are hidden inside various items and appliances such as computers, cellphones, DVDs, iPods, cameras, sensors, doorbells, and toys of children. The dark stripe on the backside of credit cards is a magnetic strip storing the relevant data of the cardholder.

Computers use hard disk drives to store information. Hard disks are memory devices where magnets alter the direction of magnetic material on disk segments. Information is processed in computers in binary language, the base-2 units of which correspond to a magnetic field aligned to either the north or the south. These fields are spun in a hard disk, and a magnetic sensor is used to read these. Inside the small speaker found in computers, televisions and radios, electrical signals are converted into sound vibrations by wire coil and magnet.

Magnets are used profusely in the industrial world. Mechanical energy is converted into electricity with the use of magnets in electric generators. On the other hand, motors use magnets to convert electricity back into mechanical work. Sorting machines using magnets are deployed in mines to separate useful metallic ores from crushed rock. In the food processing industry magnets are used for removing small metallic particles from grains and other food.

Magnetism and magnetic materials have been subjects of considerable interest for more than 3000 years, going back to ancient times. In modern times, myriad are the applications of magnetism and magnetic materials ranging from generation of electrical power to communications and information storage. Magnetic materials are absolutely indispensable in modern technology, and the intensity and importance of their applications are reflected in the multi-billion dollar market for magnetic materials in three broad areas: permanent magnets, soft magnets, and the magnetic recording medium. Continuous evolution in the field of magnetic materials has not, however, remained confined only to these well-identified areas. It is now well recognized that fresh applications are possible through the coupling of magnetism with other physical properties of materials such as magneto-thermal, magneto-elastic, magneto-optic, and magneto-electrical couplings. Newer classes of magnetic materials are being discovered with interesting new functions stimulating further growth of newer technology in various areas including information technology, wireless communication, microelectronics, biotechnology, and such like.

Against this backdrop, it is natural that the subject of magnetism finds a prominent place in solid state/condensed matter physics textbooks taught in the advanced undergraduate and postgraduate courses at universities all over the world. However, this coverage is mostly confined to a basic understanding of the phenomenon of magnetism as one of the physical properties of solid materials within the general framework of quantum mechanics. Detailed theoretical exposition of the subject is left to the specialized books on magnetism, and there are not too many of such books. Unlike high energy and particle physics, magnetism with its huge potential in technological applications is mostly an experimental science, where experimental techniques and related instruments play a very crucial role. The quantum many-body theories of magnetism (and for that matter condensed matter physics in general) are continuously evolving to explain the classes of emerging phenomena being discovered through experimental work on magnetic materials (and other classes of condensed matter). It is experimentation which is leading the field in the case of condensed matter/magnetism rather than theory as in the case of high energy and particle physics.

In the area of high energy and particle physics, the students are at least aware of the necessary theoretical techniques and the relevant experimental methods before they enter the research field at the Ph.D. level.

The book begins with an exposition of the interesting history of magnetism and magnetic materials. This is followed by a short chapter discussing the role of magnetism and magnetic materials in modern society and current technological applications of magnetic materials and devices. This second chapter highlights why magnetism is considered to be more of an applied or experiemntal science rather than a theoretical one.