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Essential Guide to Computer Data Storage: From Floppy to DVD, The by Andrei Khurshudov

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Basic Principles of Magnetic Recording

Magnetic Materials and Hysteresis Loop

A long time ago mankind discovered some natural materials, called the lodestones, that could attract another lodestone or small pieces of iron. If a piece of this material is suspended in the air, it aligns itself to follow the north-south direction. These materials are called natural magnets.

A magnet has two poles: north (positive) and south (negative). But if the magnet is cut into two parts, each of them will again have two opposite poles. Thus, the magnet may have more than two poles but always an equal number of north and south poles. Also, it is impossible to make a magnet with only one pole. Magnetic poles produce the magnetic field, as shown in Figure 3-2

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