المصدر : دي كالستر _ الخواص المغناطيسية

Magnetism, the phenomenon by which materials assert an attractive or repulsive
force or influence on other materials, has been known for thousands of years. However,
the underlying principles and mechanisms that explain the magnetic phenomenon
are complex and subtle, and their understanding has eluded scientists until
relatively recent times. Many of our modern technological devices rely on magnetism
and magnetic materials; these include electrical power generators and transformers,
electric motors, radio, television, telephones, computers, and components
of sound and video reproduction systems.
Iron, some steels, and the naturally occurring mineral lodestone are well-known
examples of materials that exhibit magnetic properties. Not so familiar, however, is
the fact that all substances are influenced to one degree or another by the presence
of a magnetic field.This chapter provides a brief description of the origin of magnetic
fields and discusses the various magnetic field vectors and magnetic parameters; the
phenomena of diamagnetism, paramagnetism, ferromagnetism, and ferrimagnetism;
some of the different magnetic materials; and the phenomenon of superconductivity.