Substances, magnetized under magnetic field, are called magnets. Some substances when the external magnetizing field increase, while others weaken. Consider first the substances, molecules which have their own magnetic field, due to the orbital motion of electrons around the nucleus. This field, like the magnetic field of a circular current. Therefore, such molecules can be imagined as tiny magnets with North and South poles.

If the substance gets into the external magnetic field, its molecules are torques, creating an ordered arrangement of the molecules along the lines of magnetic induction. Moreover, the lines of induction enter the molecule from its South pole, and out of it from the North pole. Therefore, within the substance there is an amplification of the magnetic field. Body, made of such substances, external magnetized field so, as shown in figure. 22.21, and. When the overlay created by matter fields in an external field the resulting magnetic field is obtained, shown in figure. 22.21, b, where you can see, what induction line was drawn inside the body. The rod of such a substance in an external field is along the lines of induction.

From the pic. 22.21 see, the rod needs to be involved in an external magnetic field, because opposite poles of magnets attract each other.

Since the thermal motion of molecules of matter of the body disrupts their ordered arrangement, the magnetization with increasing temperature is reduced. If the body is removed from the external field, the chaotic motion of molecules will lead to its complete demagnetization.

From the above it follows, relative magnetic permeability of such magnetic units more. (So, the manganese μ = 1,0038, aluminum has μ = 1,000023, the nitrogen μ = 1,000000013.) Substances, have the magnetic permeability slightly larger μ₀, called paramagnetic.

So, paramagnetic properties of substances explain the orbital motion of electrons around the nucleus of atoms, create their own magnetic field molecules. Note, the very weakly magnetized paramagnetic.

Differently behave in an external magnetic field of the substance, molecules which do not have their own magnetic field. The body of such substance is magnetized so, what's inside of the body its own magnetic Iole directed towards external field (rice. 22.22, and). Therefore, within the matter field is somewhat weaker, than outside; induction line as if pushed away from the body (rice. 22.22, b). The relative magnetic permeability of such magnetic materials is slightly less than unity. (For example, in bismuth μ=0,999824, silicon μ=0,999837, the water μ=0,999991, for hydrogen, μ=0,999999937.)

Substances, have the magnetic permeability slightly less than μ₀, call diamagnetic. Diamagnetic properties of matter appear even weaker, than paramagnetic properties. A typical diamagnetic bismuth is. From the pic. 22.22, b seen, the diamagnetic needs to be pushed from an external magnetic field, because the same poles of magnets repel each other. The reason is diamagnetic properties of substances will be discussed in the next Chapter.

In addition to the above, there is a small group of substances, whose relative magnetic permeability is many times greater than one. Substances, whose magnetic permeability is many times more μ₀, call ferromagnetics. The most prominent representative of these substances is iron. It can amplify the external magnetic field thousands of times. Ferromagnetics are also steel, iron, Nickel, cobalt, a rare metal gadolinium and certain alloys of ferromagnetic metals. The effect of "retract" lines of induction of the external field in the ferromagnetic material is expressed very strongly (rice. 22.23).

Study of the structure of ferromagnets with a microscope showed, the ferromagnet consists of many spontaneously (spontaneously) magnetized areas of a size of about 0,001 mm, which were called domains, and. In each domain the magnetic moments of all its molecules oriented in the same direction.

If the ferromagnetic material is not magnetized, the domains are randomly distributed in it (rice. 22.24, and). When a ferromagnet is placed in an external magnetic field, his domains peremagnichivaniya thus, their magnetic moments are directed along the lines of induction of the external field (are oriented in the direction of the field) and amplify it many times (rice. 22.24, b).

For ferromagnets belong to such substances, which consist of domains. When the directions of magnetic fields of all the domains coincides with the direction of the external field, the ferromagnetic material will be magnetized to the limit. This state is called ferromagnetic magnetic saturation. Note, that each separate domain is always magnetized to saturation.

Explanation of the ferromagnetic properties was found after, as established, electrons, in addition to the orbital motion around the nucleus, revolve around its axis, t. e. have their own momentum, dubbed "the spin" (the English word, meaning "swirling").

Since the electron is charged, it must have its own magnetic moment. The magnetic moments of electrons in an atom can have only two mutually opposite directions: parallel and antiparallel. In most cases, the magnetic moments of the electrons in the atoms are pairwise opposite direction, therefore, their magnetic field is compensated.

The atoms of ferromagnetics have a few electrons, the magnetic moments of which are not compensated, as it is directed to one side. These electrons intensify the magnetic field around the atom. Since nearby atoms interact with each other, sharing of valence electrons, the magnetic moments of these atoms are parallel, t. e. in substance arise domains.

Thus, magnetic properties of ferromagnets due to the presence of uncompensated spins of the electrons from their atoms and electrical interactions between atoms, occur when sharing of valence electrons.