To one degree or another, all substances have magnetic properties, however, those that belong to the class of ferromagnets have their own structure that allows them to hold a directed field. This quality is widely used to record information on layers, the surface of which can be oriented, creating a "memory". During magnetization, a physical phenomenon is used, which can be described by the word “delay”. Graphically depicts the so-called hysteresis loop.
Ferromagnets have the ability to magnetize spontaneously, domains are present in their molecular structure, that is, centers of magnetization, however, the multidirectional 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 effect, 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 to 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 of 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 will be required to reorient the domains. The hysteresis loop is a graphically expressed ambiguity loop of tension values relative 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, bodies also change their sizes ambiguously, and their graphs - the same hysteresis loop. Inertia is inherent in any physical processes.
The property of ferromagnets to maintain 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 created by it. Then, as the equipment improved, they began to use a tape with a layer of powder substance deposited on it, which has stronger magnetic properties, however, the general principle remained unchanged. A hysteresis loop of a ferromagnet creates the conditions for storing the information recorded on this material.
Nowadays, household tape recorders are practically not used, however, this does not mean that the principle of their work has lost its significance. In modern computers, the same principle of magnetic recording is used to accumulate information on hard drives, which is based on a hysteresis loop.