TABLE OF CONTENTS 
Magnet materials in action. The audio-frequency transformer on the left has a soft magnetic core. The DC motor on the right has a hard (permanent) magnetic stator and a soft magnetic rotor
Migrating birds, some think, navigate using the earth's magnetic field. This may be questionable, but what is beyond question is that sailors, for centuries, have navigated in this way, using a natural magnet, lodestone, to track it. Lodestone is a mineral, magnetite (Fe 3O 4), which sometimes occurs naturally in a magnetized state. Today we know lodestone as one of a family of ferrites, members of which can be found in every radio, television set and microwave oven. Ferrites are one of two families of magnetic material; the other is the ferro-magnet family, typified by iron but also including nickel, cobalt and alloys of all three. Placed in a magnetic field, these materials become magnetized, a phenomenon called magnetic induction; on removal, some, called soft magnets, lose their magnetization, others, the hard magnets, retain it.
Magnetic fields are created by moving electric charge electric current in electromagnets, electron spin in atoms of magnetic materials. This chapter is about magnetic materials: how they are characterized, where their properties come from and how they are selected and used. It starts with definitions of magnetic properties and the way they are measured. As in other chapters, charts display them well, separating the materials that are good for one sort of application from...
