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, to explain these seemingly simple phenomena based on the fundamental principles of physics has only been possible relatively recently. There are two magnets different types. Some are so-called permanent magnets, made from “hard magnetic” materials. Their magnetic properties are not related to the use of 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 the wire of the winding surrounding the core passes electricity.
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 bar permanent 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 in the space around the magnet magnetic field. 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 extend into the surrounding space from the magnet at its north pole, enter the magnet at its south pole, and pass inside the magnet material from the south pole back to the north, forming a closed loop. Full number The induction lines coming out of 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 universal meaning 4pХ10-7 H/m. In many materials, 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 a DC battery. 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 very a large number 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 switching off external field. 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”. Obviously, 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 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 the value (-H) to zero and then an increase in positive values of H will lead to the closure of the hysteresis loop through the 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 soft magnetic 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 every atom magnetic substance is a tiny magnet, or magnetic dipole, so that complete magnetization of a substance is achieved when all the individual atomic magnets are aligned in 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 "domain", which became important contribution V modern theory magnetism. Weiss imagined domains as small “colonies” of atoms, within which magnetic moments 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 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 crystal lattice, which stops her. By increasing the field strength, you can force the wall to move further, through 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 initial position, so that 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 that have 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 strong interaction between individual dipoles, leading to their ordered parallel alignment (Fig. 7, b). 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 compelling experimental confirmation 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 it to the sample and move it away from it strong magnet, the sample will be magnetized and remagnetized. Abrupt changes in the magnetization of the sample change 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 reverse 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 refer 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 category includes substances with pronounced magnetic properties, similar properties gland. 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 precess in a magnetic field (like a regular top under the influence of torque, created by force severity) with a frequency that can be measured. In addition, a force acts on free charged particles moving at right angles to the magnetic induction lines, just like 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 this circular motion equal to
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 this material. In the first case, the resonance is called magnetic, and in the second - cyclotron (due to the similarity with the cyclic movement 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. Important It has angular velocity precession. 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 of a nuclear monitoring installation 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 ah and molecules are inhomogeneous because they are distorted atomic charges, and the details of the course of the experimental resonance curve are determined local field in the area where the precessing core 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 the formulas for the series 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 an external field 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 are mutually compensated (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 of a 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
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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 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 is exclusively beneficial influence on the health of all living beings on the planet, 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 to the magnet 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, and stop various types of 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 the 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, Neodymium magnet, having a force of 200 gauss, weighs approximately 1 gram, and an ordinary iron magnet, having 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 was even mentioned in the medical treatise of Emperor Huangdi. In ancient China, it was generally accepted that human health largely depended on circulation in the body internal energy Qi, 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 of Ancient Egypt have been preserved, providing direct evidence of the use of 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 a magnetic tape on her 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. Eat documentary evidence, which describe the use of magnets to increase muscle strength, bone strength, reduce joint pain, and improve genitourinary function.
At the end of XV - early XVI centuries, some European scientists begin to study magnetic therapy as a science and its use for medicinal purposes. Even the court doctor Queen of England Elizabeth I, 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 a magnet on human health is so high that it gives him additional 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 medical society, in which research was carried out in the field of the use of magnetic fields, discovered the fact that magnets can be effectively used in the fight against many diseases of the 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 kinds jewelry made 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 the American Civil War (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 gained especially noticeable development in the Midwest. Mostly people are not the best, there weren't 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 the motor nerves" and are therefore 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 (when creating 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 the positive effect of the magnetic field on damaged spinal discs after injuries, as well as a significant reduction in pain.
Numerous medical experiments conducted at US universities showed that the appearance of joint diseases occurs due to insufficient blood circulation and disruption of the nervous system. If the cells do not receive nutrients in the required quantities, 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 these diseases, but it is most 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, a large number of similar experiments are known, and similar results are observed everywhere: 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.
It is difficult to find a field in which magnets would not be used. Educational toys, useful accessories and complex industrial equipment are just a small fraction of the truly huge number of options for their use. At the same time, few people know how magnets work and what is the secret of their attractive force. To answer these questions, you need to dive into the basics of physics, but don't worry - the dive will be short and shallow. But after getting acquainted with the theory, you will learn what a magnet consists of, and the nature of its magnetic force will become much clearer to you.
Electron is the smallest and simplest magnet
Any substance consists of atoms, and atoms, in turn, consist of a nucleus around which positively and negatively charged particles - protons and electrons - rotate. The subject of our interest is precisely electrons. Their movement creates an electric current in the conductors. In addition, each electron is a miniature source of a magnetic field and, in fact, a simple magnet. It’s just that in the composition of most materials the direction of movement of these particles is chaotic. As a result, their charges balance each other. And when the direction of rotation large quantity electrons in their orbits coincide, then a constant magnetic force arises.
Magnet device
So, we've sorted out the electrons. And now we are very close to answering the question of how magnets are structured. In order for a material to attract an iron piece of rock, the direction of the electrons in its structure must coincide. In this case, the atoms form ordered regions called domains. Each domain has a pair of poles: north and south. A constant line of movement of magnetic forces passes through them. They enter the south pole and exit the north pole. This arrangement means that the north pole will always attract the south pole of another magnet, while like poles will repel.
How a magnet attracts metals
Magnetic force does not affect all substances. Only certain materials can be attracted: iron, nickel, cobalt and rare earth metals. An iron piece of rock is not a natural magnet, but when exposed to a magnetic field, its structure is rearranged into domains with north and south poles. Thus, steel can be magnetized and retain its changed structure for a long time.
How are magnets made?
We have already figured out what a magnet consists of. It is a material in which the orientation of the domains coincides. A strong magnetic field or electric current can be used to impart these properties to the rock. IN currently people have learned to make very powerful magnets, the force of attraction of which is tens of times greater than their own weight and lasts for hundreds of years. We are talking about rare earth supermagnets based on neodymium alloy. Such products weighing 2-3 kg can hold objects weighing 300 kg or more. What does a neodymium magnet consist of and what causes such amazing properties?
Simple steel is not suitable for successfully producing products with a powerful force of attraction. This requires a special composition that will allow the domains to be ordered as efficiently as possible and maintain the stability of the new structure. To understand what a neodymium magnet consists of, imagine a metal powder of neodymium, iron and boron, which, using industrial installations, will be magnetized by a strong field and sintered into a rigid structure. To protect this material, it is coated with a durable galvanized shell. This production technology allows us to produce products of various sizes and shapes. In the assortment of the World of Magnets online store you will find a huge variety of magnetic products for work, entertainment and everyday life.
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 (the figure shows green), which come out of the north pole of the magnet and enter the south. The denser the lines of force, the more concentrated the magnetism. North Pole 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 crystal structure formed by atoms grouped into magnetic domains. The magnetic poles of the domains usually have different directions (red arrows) and do not have a net magnetic effect.
Formation of a permanent magnet
- Typically, iron's magnetic domains are randomly oriented (pink arrows), and the metal's natural magnetism does not appear.
- 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).
- Most of the magnetic domains of iron quickly align along the magnetic field lines. As a result, the iron itself becomes a permanent magnet.
In an electromagnet, the magnetic field is generated by a change electric field, or due to the movement of the conductor with DC, or due to flow through the conductor alternating current. In any case, when the current is turned off, the magnetic effect disappears. A permanent magnet is a completely different matter. There is no trace of current here. But there is a magnetic field.
A rigorous explanation of the principle of operation of a permanent magnet is impossible without the involvement of the apparatus quantum physics. If you explain it “on your fingers”, then the most adequate explanation sounds in the following way. Each electron itself is a magnet and has a magnetic moment - this is its integral physical property. If the atoms to which the electrons “belong” are randomly oriented in a substance, then the magnetic moments of the electrons compensate each other and the substance does not exhibit magnetic properties. If for some reason the atoms (at least some part of them) are oriented in one direction, then the magnetic properties of the electrons add up and the substance becomes a magnet. It turns out that a strong magnet is one in which many atoms are oriented in the same direction, and the fewer atoms have the same orientation, the weaker the magnet is. It is also clear that liquids and gases, in principle, cannot be magnets - after all, atoms can maintain their orientation only in solids.
Over time, magnets lose their properties, but this happens under the influence of external reasons: external magnetic field, high temperature, mechanical damage. When attracting a body, a magnet spends part of its energy on this attraction and becomes slightly less strong. But when you tear this body away from the magnet, it completely returns the spent energy. Thus, the total mechanical work of the permanent magnet remains zero, and theoretically the magnet can retain its properties for an indefinitely long time.
Production and use of permanent magnets
Despite the fact that magnets were known to people thousands of years ago, they industrial production became possible only in the twentieth century. Moreover, the strongest permanent magnets based on neodymium alloys were invented only in the 80s of the last century. And the cheapest and most popular magnets produced today - polymer magnetic materials, which include, for example, magnetic vinyl, were developed at the turn of the second and third millennia.
First practical use permanent magnets date back to the 12th century and have not lost their relevance to this day. This is the use of a magnetic needle in a compass. Before the start of mass production of magnetic materials, magnets were not used for anything else (using them as toys or “healing” amulets does not count).
In modern technology, permanent magnets are used everywhere. It is enough to list magnetic storage media (from disk drives in your computer to the magnetic stripe in your plastic card), microphones and speakers (there are permanent magnets in the sound speakers on your desk and in your mobile phone), in electric motors and generators (not all types of electric motors use permanent magnets, but, for example, the fans in your computer definitely have them), in numerous electronic sensors (have you ever thought that it is this type of sensor, for example, that prevents an elevator from starting to move when the doors are not closed) and in many other devices. Some types of applications of magnets are gradually becoming obsolete: for example, cathode ray tubes, on the basis of which until recently 100% of TVs and monitors were produced, are no longer relevant; Magnetic storage media are gradually disappearing from the scene. But in general, the production and use of permanent magnets is growing every year.