Hysteresis loop and its application in magnetic recording

To some extent, all substances have magnetic properties, however, those of them that belong to the class of ferromagnets have their own structure that allows to keep the directed field. This quality is widely used to record information on layers, the surface of which can be oriented, creating a "memorization". During magnetization, a physical phenomenon is used, which can be described by the word "delay". Graphically it is represented by the so-called hysteresis loop.

Ferromagnets have the ability to magnetize spontaneously, in their molecular structure there are domains, that is, foci of magnetization; however, the opposite direction of the lines of force compensates their action mutually, and therefore a piece of ordinary iron or nickel does not produce its own magnetic field.

In order for a ferromagnet to become a magnet, the magnetic fields of the domains need to be oriented in one direction, for which they must be subjected to an external field action, during which the hysteresis loop appears.

An increase in the intensity of the magnetic field around the ferromagnet leads to the orientation of previously chaotic domains, and the creation of their own directed field, while the plot of these two parameters has an upper saturation point, in which the material becomes a single domain. When creating the reverse direction field, you can reach the lower saturation point, but the chart line will not repeat its forward stroke, but will be shifted back, since additional energy is required to reorient the domains. The hysteresis loop is a graphically expressed loop of ambiguity of the strength values with respect to induction in the forward and backward directions.

Actually, many mechanical processes are also characterized by a delay associated with a change in the direction of the effect on the opposite. For example, for elastic deformations, the bodies also change their dimensions ambiguously, and their graphs have the same hysteresis loop. Inertia is inherent in any physical processes.

The property of ferromagnets to retain their magnetization is the basis of the principle of magnetic recording.

In the first tape recorders iron wire was used as the carrier, which, moving past the recording head, which is an inductor, was magnetized depending on the intensity of the field it created. Then, as the equipment improved, the tape with a layer of powdered material with stronger magnetic properties was applied to it, however, the general principle remained unchanged. The hysteresis loop of a ferromagnet creates the conditions for storing the information recorded on this material.

Household tape recorders are not used today, however, this does not mean that the principle of their work has lost its significance. In modern computers, for the accumulation of information on hard disks, the same principle of magnetic recording is used, based on the hysteresis loop.