To one degree or another, all substances have magnetic properties, however, those of them that belong to the class of ferromagnets have their own structure, which allows them to keep a directed field. This quality is widely used to record information on layers whose surface can be oriented, creating a "memory". During magnetization, a physical phenomenon is used, which can be described by the word "lag". Graphically, it is represented by the so-called hysteresis loop.
Ferromagnets have the ability to magnetize spontaneously, their molecular structure contains domains, that is, centers of magnetization, however, the multidirectionality of the lines of force mutually compensate for their action, and therefore a piece of ordinary iron or nickel does not create its own magnetic field.
In order for a ferromagnet to become a magnet, the magnetic fields of the domains must be oriented in one direction, for which they must be subjected to an external field action, during which a hysteresis loop appears.
Increasing the intensity of the magnetic field around a ferromagnet leads to an earlier orientationchaotic domains, and the creation of their own directed field, while the graph of the dependence of these two parameters has an upper saturation point, at which the material becomes single-domain. When creating a field in the opposite direction, it is possible to reach the lower saturation point, but the line of the diagram will not repeat its direct course, 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 intensity values with respect to induction in the forward and reverse directions.
Actually, many mechanical processes are also characterized by a delay associated with a change in the direction of action to the opposite. For example, under elastic deformations, the bodies also change their dimensions ambiguously, and their graphs are 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, an iron wire was used as a carrier, which, passing by the recording head, which is an inductor, was magnetized depending on the intensity of the field it created. Then, as the equipment improved, they began to use a tape with a layer of a powder substance deposited on it, which has stronger magnetic properties, however, the general principle remained unchanged. The hysteresis loop of a ferromagnet creates the conditions for preserving thethis material information.
Household tape recorders are practically not used today, however, this does not mean that the principle of their operation has lost its significance. In modern computers, the same principle of magnetic registration, which is based on a hysteresis loop, is used to accumulate information on hard drives.
