People have known about the healing properties of magnets since ancient times. The idea of ​​the influence of the magnetic field among our ancestors was formed gradually and was based on numerous observations. The first descriptions of what magnetic therapy provides to humans date back to the 10th century, when healers used magnets to treat muscle spasms. Later they began to be used to get rid of other ailments.

The influence of magnets and magnetic fields on the human body

The magnet is considered one of the most ancient discoveries made by people. In nature, it occurs in the form of magnetic iron ore. Since ancient times, people have been interested in the properties of magnets. Its ability to cause attraction and repulsion forced even the most ancient civilizations to turn to this rock special attention as a unique natural creation. The fact that the population of our planet exists in a magnetic field and is affected by it, as well as the fact that the Earth itself is a giant magnet, has been known for a long time. Many experts believe that the Earth's magnetic field has an extremely beneficial effect on the health of all living beings on the planet, while others have a different opinion. Let's turn to history and see how the idea of ​​the influence of a magnetic field was formed.

Magnetism got its name from the city of Magnesiina-Meandre, located on the territory of modern Turkey, where deposits of magnetic iron ore were first discovered - a stone with unique properties to attract iron.

Even before our era, people had an idea of ​​​​the unique energy of a magnet and a magnetic field: there was not a single civilization in which magnets were not used in some form to improve human health.

One of the first items for practical application The magnet became a compass. The properties of a simple oblong piece of magnetic iron suspended on a thread or attached to a plug in water were revealed. During this experiment, it turned out that such an object is always located in a special way: one end points to the north, and the other to the south. The compass was invented in China around 1000 BC. e., and in Europe it became known only from the 12th century. Without such a simple, but at the same time unique magnetic navigation device, there would be no great geographical discoveries XV-XVII centuries.

In India, there was a belief that the sex of the unborn child depended on the position of the spouses' heads during conception. If the heads are located to the north, then a girl will be born, if to the south, then a boy will be born.

Tibetan monks, knowing about the influence of magnets on humans, applied magnets to the head to improve concentration and increase learning ability.

There are many other documented evidence of the use of magnet in ancient India and Arab countries.

Interest in the influence of magnetic fields on the human body appeared immediately after the discovery of this unique phenomenon, and people began to attribute the most amazing properties. It was believed that finely crushed “magnetic stone” was an excellent laxative.

In addition, such properties of the magnet were described as the ability to cure dropsy and insanity, stop various types bleeding. In many documents that have survived to this day, recommendations are often given that are contradictory. For example, according to some healers, the effect of a magnet on the body is comparable to the effect of poison, while according to others, it should, on the contrary, be used as an antidote.

Neodymium magnet: healing properties and effects on human health

The greatest influence on humans is attributed to neodymium magnets: they have chemical formula NdFeB (neodymium - iron - boron).

One of the advantages of such stones is the ability to combine small sizes and strong exposure to a magnetic field. For example, a neodymium magnet with a force of 200 gauss weighs approximately 1 gram, and an ordinary iron magnet with the same strength weighs 10 grams.

Neodymium magnets have another advantage: they are quite stable and can retain their magnetic properties for many hundreds of years. The field strength of such stones decreases by about 1% over 100 years.

There is a magnetic field around each stone, which is characterized by magnetic induction, measured in Gauss. By induction you can determine the strength of the magnetic field. Very often, the strength of a magnetic field is measured in tesla (1 Tesla = 10,000 gauss).

The healing properties of neodymium magnets include improving blood circulation, stabilizing blood pressure, and preventing the occurrence of migraines.

What does magnetic therapy do and how does it affect the body?

History of magnetic therapy as a method of use healing properties The use of magnets for medicinal purposes began about 2000 years ago. IN Ancient China Magnetic therapy is even mentioned in the medical treatise of Emperor Huangdi. In Ancient China, it was generally accepted that human health largely depended on the circulation of internal energy Qi in the body, formed from two opposite principles - yin and yang. When the balance of internal energy was disturbed, a disease arose that could be cured by applying magnetic stones to certain points of the body.

As for magnetic therapy itself, many documents from the period have been preserved Ancient Egypt providing direct evidence of use this method to restore human health. One of the legends of that time talks about the unearthly beauty and health of Cleopatra, which she possessed thanks to constantly wearing magnetic tape on the head.

A real breakthrough in magnetic therapy occurred in Ancient Rome. In the famous poem “On the Nature of Things” by Titus Lucretius Cara, written back in the 1st century BC. e., it is said: “It also happens that alternately a type of iron can bounce off a stone or be attracted to it.”

Both Hippocrates and Aristotle described the unique therapeutic properties of magnetic ore, and the Roman physician, surgeon and philosopher Galen identified the pain-relieving properties of magnetic objects.

At the end of the 10th century, one Persian scientist described in detail the effect of a magnet on the human body: he assured that magnetotherapy can be used for muscle spasms and numerous inflammations. There is documented evidence that describes the use of magnets to increase muscle strength, bone strength, reduce joint pain and improve the performance of the genitourinary system.

At the end of the 15th - beginning of the 16th centuries, some European scientists began to study magnetic therapy as a science and its use for medicinal purposes. Even the court physician of Queen Elizabeth I of England, who suffered from arthritis, used magnets for treatment.

In 1530, the famous Swiss doctor Paracelsus, having studied how magnetotherapy works, published several documents that contained evidence of the effectiveness of the magnetic field. He described the magnet as “the king of all mysteries” and began using different poles of the magnet to achieve certain results in treatment. Although the doctor knew nothing about the Chinese concept of Qi energy, he similarly believed that natural force (archaeus) was capable of endowing a person with energy.

Paracelsus was confident that the influence of magnets on human health is so high that it gives him extra energy. In addition, he noted the ability of archaeus to stimulate the process of self-healing. Absolutely all inflammations and numerous diseases, in his opinion, can be treated much better with a magnet than with the use of conventional medical means. Paracelsus used magnets in practice to combat epilepsy, bleeding and indigestion.

How does magnetic therapy affect the body and what does it treat?

At the end of the 18th century, magnets began to be widely used to get rid of various diseases. The famous Austrian doctor Franz Anton Mesmer continued his research into how magnetic therapy affects the body. First in Vienna, and later in Paris, he quite successfully treated many diseases with the help of a magnet. He was so imbued with the issue of the impact of the magnetic field on human health that he defended his dissertation, which was later taken as the basis for the research and development of the doctrine of magnetic therapy in Western culture.

Relying on his experience, Mesmer made two fundamental conclusions. The first was that the human body is surrounded by a magnetic field, an influence he called “animal magnetism.” He considered the unique magnets themselves acting on humans to be conductors of this “animal magnetism.” The second conclusion was based on the fact that the planets have a great influence on the human body.

The great composer Mozart was so amazed and delighted by Mesmer’s successes in medicine that in his opera “Cosi fan tutte” (“This is what everyone does”) he sang this unique feature of the action of a magnet (“This is a magnet, Mesmer’s stone, which came from Germany and became famous in France ").

Also in Great Britain, members of the Royal Society of Medicine, which carried out research into the use of magnetic fields, discovered the fact that magnets can be effectively used in the fight against many diseases nervous system.

In the late 1770s, the French Abbé Lenoble spoke about the cures that magnetic therapy could provide when speaking at a meeting of the Royal Society of Medicine. He reported his observations in the field of magnetism and recommended the use of magnets, taking into account the location of application. He also initiated the mass creation of magnetic bracelets and various types of jewelry from this material for recovery. In his works, he examined in detail the successful results of treating toothache, arthritis and other diseases, and overexertion.

Why is magnetic therapy needed and how is it useful?

After Civil War in the USA (1861-1865), magnetic therapy became no less popular than in this method treatment due to the fact that living conditions were far from Europe. It has gained especially noticeable development in the Midwest. Mostly people are not the best, there were not enough professional doctors, which is why I had to self-medicate. At that time, a huge number of different magnetic products with an analgesic effect were produced and sold. Many advertisements mentioned unique properties magnetic therapeutic agents. Magnetic jewelry was most popular among women, while men preferred insoles and belts.

In the 19th century, many articles and books described why magnetic therapy was needed and what its role was in the treatment of many diseases. For example, a report from the famous French Salpêtrière hospital stated that magnetic fields have the property of increasing “electrical resistance in motor nerves"and therefore are very useful in the fight against hemiparesis (one-sided paralysis).

In the 20th century, the properties of magnets began to be widely used both in science (in the creation of various equipment) and in everyday life. Permanent magnets and electromagnets are located in generators that produce current and in electric motors that consume it. Many vehicles used the power of magnetism: a car, a trolleybus, a diesel locomotive, an airplane. Magnets are an integral part of many scientific instruments.

In Japan, the health effects of magnets have been the subject of much debate and intense research. So-called magnetic beds, which are used by the Japanese to relieve stress and charge the body with “energy,” have become extremely popular in this country. According to Japanese experts, magnets are good for overwork, osteochondrosis, migraines and other diseases.

The West borrowed the traditions of Japan. Methods for using magnetic therapy have found many adherents among European doctors, physiotherapists and athletes. In addition, given the benefits of magnetic therapy, this method has received support from many American specialists in the field of physical therapy, for example, leading neurologist William Phil Pot from Oklahoma. Dr. Phil Pot believes that exposing the body to a negative magnetic field stimulates the production of melatonin, the sleep hormone, and thus makes the body more calm.

Some American athletes note positive influence magnetic field on damaged spinal discs after injuries, as well as a significant reduction in pain.

Numerous medical experiments conducted at US universities have shown that the appearance of joint diseases occurs due to insufficient blood circulation and disruption of the nervous system. If the cells do not enter nutrients in the right amount, this can lead to the development of a chronic disease.

How does magnetic therapy help: new experiments

The first answer in modern medicine to the question “how does magnetic therapy help” was given in 1976 by the famous Japanese doctor Nikagawa. He introduced the concept of “magnetic field deficiency syndrome.” After a number of studies, the following symptoms of this syndrome were described: general weakness, increased fatigue, decreased performance, sleep disturbances, migraines, pain in the joints and spine, changes in the functioning of the digestive and cardiovascular systems (hypertension or hypotension), changes in the skin, gynecological dysfunctions. Accordingly, the use of magnetic therapy makes it possible to normalize all these conditions.

Of course, the lack of a magnetic field does not become the only cause of the listed diseases, but it constitutes a large part of the etiology of these processes.

Many scientists continued to conduct new experiments with magnetic fields. Perhaps the most popular of them was an experiment with a weakened external magnetic field or its absence. At the same time, it was necessary to prove the negative impact of such a situation on the human body.

One of the first scientists to conduct such an experiment was Canadian researcher Ian Crane. He looked at a number of organisms (bacteria, animals, birds) that were in a special chamber with a magnetic field. It was significantly smaller than the Earth's field. After the bacteria spent three days in such conditions, their ability to reproduce decreased 15 times, neuromotor activity in birds began to manifest much worse, and serious changes in metabolic processes began to be observed in mice. If the stay in conditions of a weakened magnetic field was longer, then irreversible changes occurred in the tissues of living organisms.

A similar experiment was carried out by a group of Russian scientists led by Lev Nepomnyashchikh: mice were placed in a chamber closed from the Earth’s magnetic field with a special screen.

A day later, they began to experience tissue decomposition. The baby animals were born bald, and subsequently they developed many diseases.

Today it is known large number similar experiments, and everywhere similar results are observed: a decrease or absence of the natural magnetic field contributes to a serious and rapid deterioration in health in all organisms studied. Numerous types of natural magnets are also now actively used, which are formed naturally from volcanic lava containing iron and atmospheric nitrogen. Such magnets were in use thousands of years ago.

MAGNETS AND MAGNETIC PROPERTIES OF MATTER
The simplest manifestations of magnetism have been known for a very long time and are familiar to most of us. However, it was only relatively recently that these seemingly simple phenomena were explained based on the fundamental principles of physics. There are two magnets different types. Some are so-called permanent magnets, made from “hard magnetic” materials. Their magnetic properties are not related to use external sources or currents. Another type includes the so-called electromagnets with a core made of “soft magnetic” iron. The magnetic fields they create are mainly due to the fact that an electric current passes through the winding wire surrounding the core.
Magnetic poles and magnetic field. The magnetic properties of a bar magnet are most noticeable near its ends. If such a magnet is hung by the middle part so that it can rotate freely in a horizontal plane, then it will take a position approximately corresponding to the direction from north to south. The end of the rod pointing north is called the north pole, and the opposite end is called the south pole. Opposite poles of two magnets attract each other, and like poles repel each other. If a bar of non-magnetized iron is brought close to one of the poles of a magnet, the latter will become temporarily magnetized. In this case, the pole of the magnetized bar closest to the magnet pole will have the opposite name, and the far pole will have the same name. The attraction between the pole of the magnet and the opposite pole induced by it in the bar explains the action of the magnet. Some materials (such as steel) themselves become weak permanent magnets after being near a permanent magnet or electromagnet. A steel rod can be magnetized by simply passing the end of a permanent bar magnet along its end. So, a magnet attracts other magnets and objects made of magnetic materials without being in contact with them. This action at a distance is explained by the existence of a magnetic field in the space around the magnet. Some idea of ​​the intensity and direction of this magnetic field can be obtained by pouring iron filings onto a sheet of cardboard or glass placed on a magnet. The sawdust will line up in chains in the direction of the field, and the density of the sawdust lines will correspond to the intensity of this field. (They are thickest at the ends of the magnet, where the intensity of the magnetic field is greatest.) M. Faraday (1791-1867) introduced the concept of closed induction lines for magnets. The induction lines exit into the surrounding space from the magnet at its north pole and enter the magnet at south pole and pass inside the magnet material from the south pole back to the north, forming a closed loop. The total number of induction lines emerging from a magnet is called magnetic flux. The magnetic flux density, or magnetic induction (B), is equal to the number of induction lines passing normally through an elementary area of ​​unit size. Magnetic induction determines the force with which a magnetic field acts on a current-carrying conductor located in it. If the conductor through which current I passes is located perpendicular to the induction lines, then according to Ampere’s law, the force F acting on the conductor is perpendicular to both the field and the conductor and is proportional to the magnetic induction, current strength and length of the conductor. Thus, for magnetic induction B we can write the expression

Where F is the force in newtons, I is the current in amperes, l is the length in meters. The unit of measurement for magnetic induction is tesla (T)
(see also ELECTRICITY AND MAGNETISM).
Galvanometer. A galvanometer is a sensitive instrument for measuring weak currents. A galvanometer uses the torque produced by the interaction of a horseshoe-shaped permanent magnet with a small current-carrying coil (a weak electromagnet) suspended in the gap between the poles of the magnet. The torque, and therefore the deflection of the coil, is proportional to the current and the total magnetic induction in the air gap, so that the scale of the device is almost linear for small deflections of the coil. Magnetizing force and magnetic field strength. Next, we should introduce another quantity characterizing the magnetic effect of electric current. Suppose that current passes through the wire of a long coil, inside of which there is a magnetizable material. The magnetizing force is the product of the electric current in the coil and the number of its turns (this force is measured in amperes, since the number of turns is a dimensionless quantity). The magnetic field strength H is equal to the magnetizing force per unit length of the coil. Thus, the value of H is measured in amperes per meter; it determines the magnetization acquired by the material inside the coil. In a vacuum, magnetic induction B is proportional to the magnetic field strength H:

Where m0 is the so-called magnetic constant having a universal value of 4pХ10-7 H/m. In many materials, the value of B is approximately proportional to H. However, in ferromagnetic materials the relationship between B and H is somewhat more complex (as discussed below). In Fig. 1 shows a simple electromagnet designed to grip loads. The energy source is battery DC. The figure also shows the field lines of the electromagnet, which can be detected by the usual method of iron filings.

Large electromagnets with iron cores and a very large number of ampere-turns, operating in continuous mode, have a large magnetizing force. They create a magnetic induction of up to 6 Tesla in the gap between the poles; this induction is limited only by mechanical stress, heating of the coils and magnetic saturation of the core. A number of giant water-cooled electromagnets (without a core), as well as installations for creating pulsed magnetic fields, were designed by P.L. Kapitsa (1894-1984) in Cambridge and at the Institute of Physical Problems of the USSR Academy of Sciences and F. Bitter (1902-1967) in Massachusetts Institute of Technology. With such magnets it was possible to achieve induction of up to 50 Tesla. A relatively small electromagnet that produces fields of up to 6.2 Tesla, consumes 15 kW of electrical power and is cooled by liquid hydrogen, was developed at the Losalamos National Laboratory. Similar fields are obtained at cryogenic temperatures.
Magnetic permeability and its role in magnetism. Magnetic permeability m is a quantity characterizing the magnetic properties of a material. Ferromagnetic metals Fe, Ni, Co and their alloys have very high maximum permeabilities - from 5000 (for Fe) to 800,000 (for supermalloy). In such materials, at relatively low field strengths H, large inductions B arise, but the relationship between these quantities, generally speaking, is nonlinear due to the phenomena of saturation and hysteresis, which are discussed below. Ferromagnetic materials are strongly attracted by magnets. They lose their magnetic properties at temperatures above the Curie point (770° C for Fe, 358° C for Ni, 1120° C for Co) and behave like paramagnets, for which the induction B up to very high strength values ​​H is proportional to it - in exactly the same as what happens in a vacuum. Many elements and compounds are paramagnetic at all temperatures. Paramagnetic substances are characterized by the fact that they become magnetized in an external magnetic field; if this field is turned off, the paramagnetic substances return to a non-magnetized state. Magnetization in ferromagnets is maintained even after the external field is turned off. In Fig. Figure 2 shows a typical hysteresis loop for a magnetically hard (with large losses) ferromagnetic material. It characterizes the ambiguous dependence of the magnetization of a magnetically ordered material on the strength of the magnetizing field. With an increase in the magnetic field strength from the initial (zero) point (1), magnetization occurs along the dashed line 1-2, and the value of m changes significantly as the magnetization of the sample increases. At point 2 saturation is achieved, i.e. with a further increase in voltage, the magnetization no longer increases. If we now gradually reduce the value of H to zero, then the curve B(H) no longer follows the previous path, but passes through point 3, revealing, as it were, a “memory” of the material about “past history,” hence the name “hysteresis.” It is obvious that in this case some residual magnetization is retained (segment 1-3). After changing the direction of the magnetizing field to the opposite direction, the B (H) curve passes point 4, and the segment (1)-(4) corresponds to the coercive force that prevents demagnetization. A further increase in the values ​​(-H) brings the hysteresis curve to the third quadrant - section 4-5. The subsequent decrease in value (-H) to zero and then increase positive values H will lead to the closure of the hysteresis loop through points 6, 7 and 2.

Hard magnetic materials are characterized by a wide hysteresis loop, covering a significant area on the diagram and therefore corresponding to large values ​​of remanent magnetization (magnetic induction) and coercive force. A narrow hysteresis loop (Fig. 3) is characteristic of magnetic soft materials- such as mild steel and special alloys with high magnetic permeability. Such alloys were created with the aim of reducing energy losses caused by hysteresis. Most of these special alloys, like ferrites, have high electrical resistance, which reduces not only magnetic losses, but also electrical losses caused by eddy currents.

Magnetic materials with high permeability are produced by annealing, carried out by holding at a temperature of about 1000 ° C, followed by tempering (gradual cooling) to room temperature. In this case, preliminary mechanical and thermal treatment, as well as the absence of impurities in the sample, are very important. For transformer cores at the beginning of the 20th century. Silicon steels were developed, the value of which increased with increasing silicon content. Between 1915 and 1920, permalloys (alloys of Ni and Fe) appeared with a characteristic narrow and almost rectangular hysteresis loop. The alloys hypernik (50% Ni, 50% Fe) and mu-metal (75% Ni, 18% Fe, 5% Cu, 2% Cr) are distinguished by especially high values ​​of magnetic permeability m at low values ​​of H, while in perminvar (45 % Ni, 30% Fe, 25% Co) the value of m is practically constant over a wide range of changes in field strength. Among modern magnetic materials, mention should be made of supermalloy - an alloy with the highest magnetic permeability (it contains 79% Ni, 15% Fe and 5% Mo).
Theories of magnetism. For the first time, the guess that magnetic phenomena are ultimately reduced to electrical phenomena arose from Ampere in 1825, when he expressed the idea of ​​​​closed internal microcurrents circulating in each atom of a magnet. However, without any experimental confirmation of the presence of such currents in matter (the electron was discovered by J. Thomson only in 1897, and the description of the structure of the atom was given by Rutherford and Bohr in 1913), this theory “faded.” In 1852, W. Weber suggested that each atom of a magnetic substance is a tiny magnet, or magnetic dipole, so that complete magnetization of a substance is achieved when all individual atomic magnets are aligned in a certain order (Fig. 4, b). Weber believed that molecular or atomic “friction” helps these elementary magnets maintain their order despite the disturbing influence of thermal vibrations. His theory was able to explain the magnetization of bodies upon contact with a magnet, as well as their demagnetization upon impact or heating; finally, the “reproduction” of magnets when cutting a magnetized needle or magnetic rod into pieces was also explained. And yet this theory did not explain either the origin of the elementary magnets themselves, or the phenomena of saturation and hysteresis. Weber's theory was improved in 1890 by J. Ewing, who replaced his hypothesis of atomic friction with the idea of ​​interatomic confining forces that help maintain the ordering of the elementary dipoles that make up a permanent magnet.

The approach to the problem, once proposed by Ampere, received a second life in 1905, when P. Langevin explained the behavior of paramagnetic materials by attributing to each atom an internal uncompensated electron current. According to Langevin, it is these currents that form tiny magnets that are randomly oriented when there is no external field, but acquire an orderly orientation when it is applied. In this case, the approach to complete order corresponds to saturation of magnetization. In addition, Langevin introduced the concept of a magnetic moment, which for an individual atomic magnet is equal to the product of the “magnetic charge” of a pole and the distance between the poles. Thus, the weak magnetism of paramagnetic materials is due to the total magnetic moment created by uncompensated electron currents. In 1907, P. Weiss introduced the concept of a “domain,” which became an important contribution to the modern theory of magnetism. Weiss imagined domains as small “colonies” of atoms, within which the magnetic moments of all atoms, for some reason, are forced to maintain the same orientation, so that each domain is magnetized to saturation. An individual domain can have linear dimensions of the order of 0.01 mm and, accordingly, a volume of the order of 10-6 mm3. The domains are separated by so-called Bloch walls, the thickness of which does not exceed 1000 atomic sizes. The “wall” and two oppositely oriented domains are shown schematically in Fig. 5. Such walls represent “transition layers” in which the direction of domain magnetization changes.

In the general case, three sections can be distinguished on the initial magnetization curve (Fig. 6). In the initial section, the wall, under the influence of an external field, moves through the thickness of the substance until it encounters a defect in the crystal lattice, which stops it. By increasing the field strength, you can force the wall to move further, through the middle section between the dashed lines. If after this the field strength is again reduced to zero, then the walls will no longer return to their original position, so the sample will remain partially magnetized. This explains the hysteresis of the magnet. At the final section of the curve, the process ends with the saturation of the magnetization of the sample due to the ordering of the magnetization inside the last disordered domains. This process is almost completely reversible. Magnetic hardness is exhibited by those materials whose atomic lattice contains many defects that impede the movement of interdomain walls. This can be achieved by mechanical and thermal treatment, for example by compression and subsequent sintering of the powdered material. In alnico alloys and their analogues, the same result is achieved by fusing metals into a complex structure.

In addition to paramagnetic and ferromagnetic materials, there are materials with so-called antiferromagnetic and ferrimagnetic properties. The difference between these types of magnetism is explained in Fig. 7. Based on the concept of domains, paramagnetism can be considered as a phenomenon caused by the presence in the material of small groups of magnetic dipoles, in which individual dipoles interact very weakly with each other (or do not interact at all) and therefore, in the absence of an external field, take only random orientations ( Fig. 7, a). In ferromagnetic materials, within each domain there is a strong interaction between individual dipoles, leading to their ordered parallel alignment (Fig. 7b). In antiferromagnetic materials, on the contrary, the interaction between individual dipoles leads to their antiparallel ordered alignment, so that the total magnetic moment of each domain is zero (Fig. 7c). Finally, in ferrimagnetic materials (for example, ferrites) there is both parallel and antiparallel ordering (Fig. 7d), which results in weak magnetism.

There are two convincing experimental confirmations of the existence of domains. The first of them is the so-called Barkhausen effect, the second is the method of powder figures. In 1919, G. Barkhausen established that when an external field is applied to a sample of ferromagnetic material, its magnetization changes in small discrete portions. From the point of view of domain theory, this is nothing more than an abrupt advance of the interdomain wall, encountering on its way individual defects that delay it. This effect is usually detected using a coil in which a ferromagnetic rod or wire is placed. If you alternately bring a strong magnet towards and away from the sample, the sample will be magnetized and remagnetized. Abrupt changes in the magnetization of the sample change the magnetic flux through the coil, and an induction current is excited in it. The voltage generated in the coil is amplified and fed to the input of a pair of acoustic headphones. Clicks heard through headphones indicate an abrupt change in magnetization. To reveal the domain structure of a magnet using the powder figure method, a drop of a colloidal suspension of ferromagnetic powder (usually Fe3O4) is applied to a well-polished surface of a magnetized material. Powder particles settle mainly in places of maximum inhomogeneity of the magnetic field - at the boundaries of domains. This structure can be studied under a microscope. A method based on the passage of polarized light through a transparent ferromagnetic material has also been proposed. Weiss's original theory of magnetism in its main features has retained its significance to this day, having, however, received an updated interpretation based on the idea of ​​uncompensated electron spins as a factor determining atomic magnetism. The hypothesis about the existence of an electron’s own momentum was put forward in 1926 by S. Goudsmit and J. Uhlenbeck, and at present it is electrons as spin carriers that are considered “elementary magnets”. To explain this concept, consider (Fig. 8) a free atom of iron, a typical ferromagnetic material. Its two shells (K and L), closest to the nucleus, are filled with electrons, with the first of them containing two and the second containing eight electrons. In the K-shell, the spin of one of the electrons is positive and the other is negative. In the L shell (more precisely, in its two subshells), four of the eight electrons have positive spins, and the other four have negative spins. In both cases, the electron spins within one shell are completely compensated, so that the total magnetic moment is zero. In the M-shell, the situation is different, since out of the six electrons located in the third subshell, five electrons have spins directed in one direction, and only the sixth in the other. As a result, four uncompensated spins remain, which determines the magnetic properties of the iron atom. (There are only two valence electrons in the outer N shell, which do not contribute to the magnetism of the iron atom.) The magnetism of other ferromagnets, such as nickel and cobalt, is explained in a similar way. Since neighboring atoms in an iron sample strongly interact with each other, and their electrons are partially collectivized, this explanation should be considered only as a visual, but very simplified diagram of the real situation.

The theory of atomic magnetism, based on taking into account the electron spin, is supported by two interesting gyromagnetic experiments, one of which was carried out by A. Einstein and W. de Haas, and the other by S. Barnett. In the first of these experiments, a cylinder of ferromagnetic material was suspended as shown in Fig. 9. If current is passed through the winding wire, the cylinder rotates around its axis. When the direction of the current (and therefore the magnetic field) changes, it turns in the opposite direction. In both cases, the rotation of the cylinder is due to the ordering of the electron spins. In Barnett's experiment, on the contrary, a suspended cylinder, sharply brought into a state of rotation, becomes magnetized in the absence of a magnetic field. This effect is explained by the fact that when the magnet rotates, a gyroscopic moment is created, which tends to rotate the spin moments in the direction of its own axis of rotation.

For a more complete explanation of the nature and origin of short-range forces that order neighboring atomic magnets and counteract the disordering influence of thermal motion, one should turn to quantum mechanics. A quantum mechanical explanation of the nature of these forces was proposed in 1928 by W. Heisenberg, who postulated the existence of exchange interactions between neighboring atoms. Later, G. Bethe and J. Slater showed that exchange forces increase significantly with decreasing distance between atoms, but upon reaching a certain minimum interatomic distance they drop to zero.
MAGNETIC PROPERTIES OF SUBSTANCE
One of the first extensive and systematic studies of the magnetic properties of matter was undertaken by P. Curie. He established that, according to their magnetic properties, all substances can be divided into three classes. The first includes substances with pronounced magnetic properties, similar to the properties of iron. Such substances are called ferromagnetic; their magnetic field is noticeable at considerable distances (see above). The second class includes substances called paramagnetic; Their magnetic properties are generally similar to those of ferromagnetic materials, but much weaker. For example, the force of attraction to the poles of a powerful electromagnet can tear an iron hammer out of your hands, and to detect the attraction of a paramagnetic substance to the same magnet, you usually need very sensitive analytical balances. The last, third class includes the so-called diamagnetic substances. They are repelled by an electromagnet, i.e. the force acting on diamagnetic materials is directed opposite to that acting on ferro- and paramagnetic materials.
Measurement of magnetic properties. When studying magnetic properties, two types of measurements are most important. The first of them is measuring the force acting on a sample near a magnet; This is how the magnetization of the sample is determined. The second includes measurements of “resonant” frequencies associated with the magnetization of matter. Atoms are tiny "gyros" and in a magnetic field precess (like a regular top under the influence of the torque created by gravity) at a frequency that can be measured. In addition, a force acts on free charged particles moving at right angles to the lines of magnetic induction, as does the electron current in a conductor. It causes the particle to move in a circular orbit, the radius of which is given by R = mv/eB, where m is the mass of the particle, v is its speed, e is its charge, and B is the magnetic induction of the field. The frequency of such circular motion is

where f is measured in hertz, e - in coulombs, m - in kilograms, B - in tesla. This frequency characterizes the movement of charged particles in a substance located in a magnetic field. Both types of motions (precession and motion in circular orbits) can be excited by alternating fields with resonant frequencies, equal to the “natural” frequencies characteristic of of this material. In the first case, the resonance is called magnetic, and in the second - cyclotron (due to its similarity with the cyclic motion of a subatomic particle in a cyclotron). Speaking about the magnetic properties of atoms, it is necessary to pay special attention to their angular momentum. The magnetic field acts on the rotating atomic dipole, tending to rotate it and place it parallel to the field. Instead, the atom begins to precess around the direction of the field (Fig. 10) with a frequency depending on the dipole moment and the strength of the applied field.

Atomic precession is not directly observable because all atoms in a sample precess at a different phase. If we apply a small alternating field directed perpendicular to the constant ordering field, then a certain phase relationship is established between the precessing atoms and their total magnetic moment begins to precess with a frequency equal to the precession frequency of individual magnetic moments. The angular velocity of precession is important. Typically, this value is on the order of 1010 Hz/T for magnetization associated with electrons, and on the order of 107 Hz/T for magnetization associated with positive charges in the nuclei of atoms. Schematic diagram installation for observing nuclear magnetic resonance (NMR) is shown in Fig. 11. The substance being studied is introduced into a uniform constant field between the poles. If a radiofrequency field is then excited using a small coil surrounding the test tube, a resonance can be achieved at a specific frequency equal to the precession frequency of all nuclear “gyros” in the sample. The measurements are similar to tuning a radio receiver to the frequency of a specific station.

Magnetic resonance methods make it possible to study not only the magnetic properties of specific atoms and nuclei, but also the properties of their environment. The fact is that magnetic fields in solids and molecules are inhomogeneous, since they are distorted by atomic charges, and the details of the experimental resonance curve are determined by the local field in the region where the precessing nucleus is located. This makes it possible to study the structural features of a particular sample using resonance methods.
Calculation of magnetic properties. The magnetic induction of the Earth's field is 0.5 * 10 -4 Tesla, while the field between the poles of a strong electromagnet is about 2 Tesla or more. The magnetic field created by any configuration of currents can be calculated using the Biot-Savart-Laplace formula for the magnetic induction of the field created by a current element. Calculation of the field created by contours different shapes and cylindrical coils, in many cases very complex. Below are formulas for a number of simple cases. The magnetic induction (in tesla) of the field created by a long straight wire with a current I (amperes), at a distance r (meters) from the wire is

The induction in the center of a circular coil of radius R with current I is equal (in the same units):

A tightly wound coil of wire without an iron core is called a solenoid. The magnetic induction created by a long solenoid with the number of turns N at a point sufficiently distant from its ends is equal to

Here, the value NI/L is the number of amperes (ampere-turns) per unit length of the solenoid. In all cases, the magnetic field of the current is directed perpendicular to this current, and the force acting on the current in the magnetic field is perpendicular to both the current and the magnetic field. The field of a magnetized iron rod is similar to the external field of a long solenoid, with the number of ampere-turns per unit length corresponding to the current in the atoms on the surface of the magnetized rod, since the currents inside the rod cancel each other (Fig. 12). By the name of Ampere, such a surface current is called Ampere. The magnetic field strength Ha created by the Ampere current is equal to the magnetic moment per unit volume of the rod M.

If an iron rod is inserted into the solenoid, then in addition to the fact that the solenoid current creates a magnetic field H, the ordering of atomic dipoles in the magnetized material of the rod creates magnetization M. In this case, the total magnetic flux is determined by the sum of the real and Ampere currents, so that B = m0(H + Ha), or B = m0(H + M). The M/H ratio is called magnetic susceptibility and is denoted by the Greek letter c; c is a dimensionless quantity characterizing the ability of a material to be magnetized in a magnetic field.
The B/H value characterizing magnetic properties
material is called magnetic permeability and is denoted by ma, with ma = m0m, where ma is absolute and m is relative permeability, m = 1 + c. In ferromagnetic substances, the value of c can have very large values ​​- up to 10 4-10 6. The value of c for paramagnetic materials is slightly greater than zero, and for diamagnetic materials it is slightly less. Only in a vacuum and in very weak fields are the quantities c and m constant and independent of the external field. The dependence of induction B on H is usually nonlinear, and its graphs, the so-called. magnetization curves for different materials and even at different temperatures can differ significantly (examples of such curves are shown in Fig. 2 and 3). The magnetic properties of matter are very complex, and their deep understanding requires a careful analysis of the structure of atoms, their interactions in molecules, their collisions in gases and their mutual influence in solids and liquids; The magnetic properties of liquids are still the least studied. - fields with a strength H? 0.5 = 1.0 ME (the border is arbitrary). The lower value of S. m.p. corresponds to the max. the value of the stationary field = 500 kOe, the swarm can be accessible to modern means. technology, upper field 1 ME, even for a short time. impact on... ... Physical encyclopedia

A branch of physics that studies the structure and properties of solids. Scientific knowledge about the microstructure of solids and the physical and chemical properties of their constituent atoms is necessary for the development of new materials and technical devices. Physics... ... Collier's Encyclopedia

A branch of physics covering knowledge of static electricity, electric currents and magnetic phenomena. ELECTROSTATICS Electrostatics deals with phenomena associated with electric charges at rest. The presence of forces acting between... ... Collier's Encyclopedia

- (from ancient Greek physis nature). The ancients called physics any study of the surrounding world and natural phenomena. This understanding of the term physics remained until the end of the 17th century. Later, a number of special disciplines appeared: chemistry, which studies the properties... ... Collier's Encyclopedia

The term moment in relation to atoms and atomic nuclei can mean the following: 1) spin moment, or spin, 2) magnetic dipole moment, 3) electric quadrupole moment, 4) other electric and magnetic moments. Various types… … Collier's Encyclopedia

Electrical analogue of ferromagnetism. Just as residual magnetic polarization (moment) appears in ferromagnetic substances when placed in a magnetic field, in ferroelectric dielectrics placed in electric field,… … Collier's Encyclopedia

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Everyone held a magnet in their hands and played with it as a child. Magnets can be very different in shape and size, but all magnets have general property- they attract iron. It seems that they themselves are made of iron, at least of some kind of metal for sure. There are, however, “black magnets” or “stones”; they also strongly attract pieces of iron, and especially each other.

But they don’t look like metal; they break easily, like glass. Magnets have many useful uses, for example, it is convenient to “pin” paper sheets to iron surfaces with their help. A magnet is convenient for collecting lost needles, so, as we can see, this is a completely useful thing.

Science 2.0 - The Great Leap Forward - Magnets

Magnet in the past

More than 2000 years ago, the ancient Chinese knew about magnets, at least that this phenomenon could be used to choose a direction when traveling. That is, they invented a compass. Philosophers in ancient Greece, curious people, collecting various amazing facts, encountered magnets in the vicinity of the city of Magnessa in Asia Minor. There they discovered strange stones that could attract iron. At that time, this was no less amazing than aliens could become in our time.

It seemed even more surprising that magnets do not attract all metals, but only iron, and iron itself can become a magnet, although not so strong. We can say that the magnet attracted not only iron, but also the curiosity of scientists, and greatly moved forward such a science as physics. Thales of Miletus wrote about the “soul of a magnet,” and the Roman Titus Lucretius Carus wrote about the “raging movement of iron filings and rings” in his essay “On the Nature of Things.” He could already notice the presence of two poles of the magnet, which later, when sailors began to use the compass, were named after the cardinal points.

What is a magnet? In simple words. Magnetic field

We took the magnet seriously

The nature of magnets could not be explained for a long time. With the help of magnets, new continents were discovered (sailors still treat the compass with great respect), but no one still knew anything about the very nature of magnetism. Work was carried out only to improve the compass, which was also done by the geographer and navigator Christopher Columbus.

In 1820, the Danish scientist Hans Christian Oersted made a major discovery. He established the action of a wire with an electric current on a magnetic needle, and as a scientist, he found out through experiments how this happens in different conditions. In the same year, the French physicist Henri Ampere came up with a hypothesis about elementary circular currents flowing in the molecules of magnetic matter. In 1831, the Englishman Michael Faraday, using a coil of insulated wire and a magnet, conducted experiments showing that mechanical work can be converted into electric current. He also establishes the law of electromagnetic induction and introduces the concept of “magnetic field”.

Faraday's law establishes the rule: for a closed loop, the electromotive force is equal to the rate of change of the magnetic flux passing through this loop. All electrical machines operate on this principle - generators, electric motors, transformers.

In 1873, Scottish scientist James C. Maxwell combines magnetic and electrical phenomena into one theory, classical electrodynamics.

Substances that can be magnetized are called ferromagnets. This name associates magnets with iron, but besides it, the ability to magnetize is also found in nickel, cobalt, and some other metals. Since the magnetic field has already entered the field of practical use, magnetic materials have become the subject of great attention.

Experiments began with alloys of magnetic metals and various additives in them. The resulting materials were very expensive, and if Werner Siemens had not come up with the idea of ​​replacing the magnet with steel magnetized by a relatively small current, the world would never have seen the electric tram and the Siemens company. Siemens also worked on telegraph devices, but here he had many competitors, and the electric tram gave the company a lot of money, and ultimately pulled everything else along with it.

Electromagnetic induction

Basic quantities associated with magnets in technology

We will be interested mainly in magnets, that is, ferromagnets, and will leave a little aside the remaining, very vast area of ​​magnetic (better said, electromagnetic, in memory of Maxwell) phenomena. Our units of measurement will be those accepted in SI (kilogram, meter, second, ampere) and their derivatives:

l Field strength, H, A/m (amps per meter).

This quantity characterizes the field strength between parallel conductors, the distance between which is 1 m, and the current flowing through them is 1 A. The field strength is a vector quantity.

l Magnetic induction, B, Tesla, magnetic flux density (Weber/m2)

This is the ratio of the current through the conductor to the length of the circle, at the radius at which we are interested in the magnitude of induction. The circle lies in the plane that the wire intersects perpendicularly. This also includes a factor called magnetic permeability. This is a vector quantity. If you mentally look at the end of the wire and assume that the current flows in the direction away from us, then the magnetic force circles “rotate” clockwise, and the induction vector is applied to the tangent and coincides with them in direction.

l Magnetic permeability, μ (relative value)

If we take the magnetic permeability of vacuum as 1, then for other materials we will obtain the corresponding values. So, for example, for air we get a value that is almost the same as for vacuum. For iron we get significantly larger values, so we can figuratively (and very accurately) say that iron “pulls” magnetic lines of force into itself. If the field strength in a coil without a core is equal to H, then with a core we get μH.

l Coercive force, A/m.

Coercive force measures how much a magnetic material resists demagnetization and remagnetization. If the current in the coil is completely removed, then there will be residual induction in the core. To make it equal to zero, you need to create a field of some intensity, but in reverse, that is, let the current flow in the opposite direction. This tension is called coercive force.

Since magnets in practice are always used in some connection with electricity, it should not be surprising that such an electrical quantity as ampere is used to describe their properties.

From what has been said, it follows that it is possible, for example, for a nail that has been acted upon by a magnet to become a magnet itself, albeit a weaker one. In practice, it turns out that even children who play with magnets know this.

There are different requirements for magnets in technology, depending on where these materials go. Ferromagnetic materials are divided into “soft” and “hard”. The first ones are used to make cores for devices where the magnetic flux is constant or variable. You cannot make a good independent magnet from soft materials. They demagnetize too easily, and this is precisely their valuable property, since the relay must “release” if the current is turned off, and the electric motor should not heat up - excess energy is spent on magnetization reversal, which is released in the form of heat.

WHAT DOES A MAGNETIC FIELD REALLY LOOK LIKE? Igor Beletsky

Permanent magnets, that is, those that are called magnets, require hard materials for their manufacture. Rigidity refers to magnetic, that is, a large residual induction and a large coercive force, since, as we have seen, these quantities are closely related to each other. Such magnets are used in carbon, tungsten, chromium and cobalt steels. Their coercivity reaches values ​​of about 6500 A/m.

There are special alloys called alni, alnisi, alnico and many others, as you might guess they include aluminum, nickel, silicon, cobalt in various combinations, which have a greater coercive force - up to 20,000...60,000 A/m. Such a magnet is not so easy to tear off from iron.

There are magnets specifically designed to operate at higher frequencies. This is the well-known “round magnet”. It is “mined” from an unusable speaker from a stereo system, or a car radio, or even a TV of yesteryear. This magnet is made by sintering iron oxides and special additives. This material is called ferrite, but not every ferrite is specifically magnetized this way. And in speakers it is used for reasons of reducing useless losses.

Magnets. Discovery. How does this work?

What happens inside a magnet?

Due to the fact that atoms of a substance are peculiar “clumps” of electricity, they can create their own magnetic field, but only in some metals that have a similar atomic structure is this ability very strongly expressed. Iron, cobalt, and nickel are located next to each other in Mendeleev’s periodic table, and have similar structures of electronic shells, which turns the atoms of these elements into microscopic magnets.

Since metals can be called a frozen mixture of various very small crystals, it is clear that such alloys can have a lot of magnetic properties. Many groups of atoms can “unfold” their own magnets under the influence of neighbors and external fields. Such “communities” are called magnetic domains, and form very bizarre structures that are still being studied with interest by physicists. This is of great practical importance.

As already mentioned, magnets can be almost atomic in size, so the smallest size of a magnetic domain is limited by the size of the crystal in which the magnetic metal atoms are embedded. This explains, for example, the almost fantastic recording density on modern hard drives computers, which will apparently continue to grow until disks have more serious competitors.

Gravity, magnetism and electricity

Where are magnets used?

The cores of which are magnets made from magnets, although usually simply called cores, magnets have many more uses. There are stationery magnets, magnets for latching furniture doors, and chess magnets for travelers. These are magnets known to everyone.

Rarer types include magnets for charged particle accelerators; these are very impressive structures that can weigh tens of tons or more. Although now experimental physics overgrown with grass, with the exception of that part that immediately brings super-profits in the market, but itself is worth almost nothing.

Another interesting magnet is installed in a fancy medical device called a magnetic resonance imaging scanner. (Actually, the method is called NMR, nuclear magnetic resonance, but in order not to frighten people who are generally not strong in physics, it was renamed.) The device requires placing the observed object (the patient) in a strong magnetic field, and the corresponding magnet has frightening dimensions and the shape of the devil's coffin.

A person is placed on a couch and rolled through a tunnel in this magnet while sensors scan the area of ​​interest to doctors. In general, it’s not a big deal, but some people experience claustrophobia to the point of panic. Such people will willingly allow themselves to be cut alive, but will not agree to an MRI examination. However, who knows how a person feels in an unusually strong magnetic field with an induction of up to 3 Tesla, after having paid good money for it.

To get this strong field, often exploit superconductivity by cooling a magnet coil with liquid hydrogen. This makes it possible to “pump up” the field without fear that heating the wires with a strong current will limit the capabilities of the magnet. This is not a cheap setup at all. But magnets made of special alloys that do not require current biasing are much more expensive.

Our Earth is also big, although not very strong magnet. It helps not only the owners of the magnetic compass, but also saves us from death. Without him we would be killed solar radiation. The picture of the Earth's magnetic field, simulated by computers based on observations from space, looks very impressive.

Here is a short answer to the question about what a magnet is in physics and technology.

Along with pieces of amber electrified by friction, permanent magnets were the first material evidence for ancient people electromagnetic phenomena(at the dawn of history, lightning was definitely attributed to the sphere of manifestation of intangible forces). Explaining the nature of ferromagnetism has always occupied the inquisitive minds of scientists, however, even now the physical nature of the permanent magnetization of some substances, both natural and artificially created, has not yet been fully revealed, leaving a considerable field of activity for modern and future researchers.

Traditional materials for permanent magnets

They have been actively used in industry since 1940 with the advent of alnico alloy (AlNiCo). Previously, permanent magnets made of various types of steel were used only in compasses and magnetos. Alnico made it possible to replace electromagnets with them and use them in devices such as motors, generators and loudspeakers.

This penetration into our daily lives received a new impetus with the creation of ferrite magnets, and since then permanent magnets have become commonplace.

The revolution in magnetic materials began around 1970, with the creation of the samarium-cobalt family of hard magnetic materials with previously unheard-of magnetic energy densities. Then a new generation of rare earth magnets was discovered, based on neodymium, iron and boron, with a much higher magnetic energy density than samarium cobalt (SmCo) and at an expectedly low cost. These two families of rare earth magnets have such high energy densities that they can not only replace electromagnets, but be used in areas that are inaccessible to them. Examples include tiny stepper motor on permanent magnets V wristwatch and sound transducers in Walkman-type headphones.

The gradual improvement in the magnetic properties of materials is shown in the diagram below.

Neodymium permanent magnets

They represent the latest and most significant development in this field over the past decades. Their discovery was first announced almost simultaneously at the end of 1983 by metal specialists from Sumitomo and General Motors. They are based on the intermetallic compound NdFeB: an alloy of neodymium, iron and boron. Of these, neodymium is a rare earth element extracted from the mineral monazite.

The enormous interest that these permanent magnets have generated arises because for the first time a new magnetic material has been produced that is not only stronger than the previous generation, but is more economical. It consists mainly of iron, which is much cheaper than cobalt, and neodymium, which is one of the most common rare earth materials and has more reserves on Earth than lead. The major rare earth minerals monazite and bastanesite contain five to ten times more neodymium than samarium.

Physical mechanism of permanent magnetization

To explain the functioning of a permanent magnet, we must look inside it down to the atomic scale. Each atom has a set of spins of its electrons, which together form its magnetic moment. For our purposes, we can consider each atom as a small bar magnet. When a permanent magnet is demagnetized (either by heating it to high temperature, or an external magnetic field), each atomic moment is oriented randomly (see figure below) and no regularity is observed.

When it is magnetized in a strong magnetic field, all atomic moments are oriented in the direction of the field and, as it were, interlocked with each other (see figure below). This coupling allows the permanent magnet field to be maintained when the external field is removed, and also resists demagnetization when its direction changes. A measure of the cohesive force of atomic moments is the magnitude of the coercive force of the magnet. More on this later.

In a more in-depth presentation of the magnetization mechanism, one does not operate with the concepts of atomic moments, but uses ideas about miniature (of the order of 0.001 cm) regions inside the magnet, which initially have permanent magnetization, but are randomly oriented in the absence of an external field, so that a strict reader, if desired, can attribute the above physical The mechanism is not related to the magnet as a whole. but to its separate domain.

Induction and magnetization

The atomic moments are summed up and form the magnetic moment of the entire permanent magnet, and its magnetization M shows the magnitude of this moment per unit volume. Magnetic induction B shows that a permanent magnet is the result of an external magnetic force (field strength) H applied during primary magnetization, as well as an internal magnetization M due to the orientation of atomic (or domain) moments. Its value in the general case is given by the formula:

B = µ 0 (H + M),

where µ 0 is a constant.

In a permanent ring and homogeneous magnet, the field strength H inside it (in the absence of an external field) is equal to zero, since, according to the law of total current, the integral of it along any circle inside such a ring core is equal to:

H∙2πR = iw=0, whence H=0.

Therefore, the magnetization in a ring magnet is:

In an open magnet, for example, in the same ring magnet, but with an air gap of width l in a core of length l gray, in the absence of an external field and the same induction B inside the core and in the gap, according to the law of total current, we obtain:

H ser l ser + (1/ µ 0)Bl zaz = iw=0.

Since B = µ 0 (H ser + M ser), then, substituting its expression into the previous one, we get:

H ser (l ser + l zaz) + M ser l zaz =0,

H ser = ─ M ser l zaz (l ser + l zaz).

In the air gap:

H zaz = B/µ 0,

wherein B is determined by the given M ser and the found H ser.

Magnetization curve

Starting from the unmagnetized state, when H increases from zero, due to the orientation of all atomic moments in the direction of the external field, M and B quickly increase, changing along section “a” of the main magnetization curve (see figure below).

When all atomic moments are equalized, M comes to its saturation value, and a further increase in B occurs solely due to the applied field (section b of the main curve in the figure below). When the external field decreases to zero, the induction B decreases not along the original path, but along section “c” due to the coupling of atomic moments, tending to maintain them in the same direction. The magnetization curve begins to describe the so-called hysteresis loop. When H (external field) approaches zero, the induction approaches a residual value determined only by atomic moments:

B r = μ 0 (0 + M g).

After the direction of H changes, H and M act in opposite directions and B decreases (part of the curve “d” in the figure). The value of the field at which B decreases to zero is called the coercive force of the magnet B H C . When the magnitude of the applied field is large enough to break the cohesion of the atomic moments, they are oriented in the new direction of the field, and the direction of M is reversed. The field value at which this occurs is called the internal coercive force of the permanent magnet M H C . So, there are two different but related coercive forces associated with a permanent magnet.

The figure below shows the main demagnetization curves various materials for permanent magnets.

It can be seen from it that NdFeB magnets have the highest residual induction B r and coercive force (both total and internal, i.e., determined without taking into account the strength H, only by the magnetization M).

Surface (ampere) currents

The magnetic fields of permanent magnets can be considered as the fields of some associated currents flowing along their surfaces. These currents are called Ampere currents. In the usual sense of the word, there are no currents inside permanent magnets. However, comparing the magnetic fields of permanent magnets and the fields of currents in coils, the French physicist Ampere suggested that the magnetization of a substance can be explained by the flow of microscopic currents, forming microscopic closed circuits. And indeed, the analogy between the field of a solenoid and a long cylindrical magnet is almost complete: there is a north and south pole of a permanent magnet and the same poles of the solenoid, and the patterns of force lines of their fields are also very similar (see figure below).

Are there currents inside a magnet?

Let's imagine that the entire volume of some bar permanent magnet (with an arbitrary shape) cross section) is filled with microscopic Ampere currents. A cross section of a magnet with such currents is shown in the figure below.

Each of them has a magnetic moment. With the same orientation in the direction of the external field, they form a resulting magnetic moment that is different from zero. It determines the existence of a magnetic field in the apparent absence of ordered movement of charges, in the absence of current through any cross section of the magnet. It is also easy to understand that inside it, the currents of adjacent (contacting) circuits are compensated. Only the currents on the surface of the body, which form the surface current of a permanent magnet, are uncompensated. Its density turns out to be equal to the magnetization M.

How to get rid of moving contacts

The problem of creating a contactless synchronous machine is known. Its traditional design with electromagnetic excitation from the poles of a rotor with coils involves supplying current to them through movable contacts - slip rings with brushes. The disadvantages of such a technical solution are well known: they are difficulties in maintenance, low reliability, and large losses in moving contacts, especially if we're talking about about powerful turbo and hydrogen generators, in the excitation circuits of which considerable electrical power is consumed.

If you make such a generator using permanent magnets, then the contact problem immediately goes away. However, there is a problem of reliable fastening of magnets on a rotating rotor. This is where the experience gained in tractor manufacturing can come in handy. They have long been using an inductor generator with permanent magnets located in rotor slots filled with a low-melting alloy.

Permanent magnet motor

In recent decades, DC motors have become widespread. Such a unit consists of the electric motor itself and an electronic commutator for its armature winding, which performs the functions of a collector. The electric motor is a synchronous motor with permanent magnets located on the rotor, as in Fig. above, with a stationary armature winding on the stator. Electronic switch circuitry is an inverter DC voltage(or current) of the supply network.

The main advantage of such a motor is its non-contact nature. Its specific element is a photo-, induction or Hall rotor position sensor that controls the operation of the inverter.

When a magnet attracts metal objects to itself, it seems like magic, but in reality the “magical” properties of magnets are associated only with the special organization of their electronic structure. Because an electron orbiting an atom creates a magnetic field, all atoms are small magnets; however, in most substances the disordered magnetic effects of atoms cancel each other out.

The situation is different in magnets, the atomic magnetic fields of which are arranged in ordered regions called domains. Each such region has a north and south pole. The direction and intensity of the magnetic field is characterized by the so-called lines of force (shown in green in the figure), which leave the north pole of the magnet and enter the south. The denser the lines of force, the more concentrated the magnetism. The north pole of one magnet attracts the south pole of another, while two like poles repel each other. Magnets attract only certain metals, mainly iron, nickel and cobalt, called ferromagnets. Although ferromagnetic materials are not natural magnets, their atoms rearrange themselves in the presence of a magnet in such a way that the ferromagnetic bodies develop magnetic poles.

Magnetic chain

Touching the end of a magnet to metal paper clips creates a north and south pole for each paper clip. These poles are oriented in the same direction as the magnet. Each paper clip became a magnet.

Countless little magnets

Some metals have a crystalline structure made up of atoms grouped into magnetic domains. The magnetic poles of domains usually have different directions (red arrows) and do not have a net magnetic effect.

Formation of a permanent magnet

1. Typically, iron's magnetic domains are randomly oriented (pink arrows), and the metal's natural magnetism does not appear.
2. If you bring a magnet (pink bar) closer to the iron, the magnetic domains of the iron begin to line up along the magnetic field (green lines).
3. Most of the magnetic domains of iron quickly align along the magnetic field lines. As a result, the iron itself becomes a permanent magnet.