The vast majority of atoms have their own magnetic field. Almost any atom can be thought of as a tiny magnet with north and south poles. This magnetic effect is explained by the fact that electrons, when moving in orbits around the atomic nucleus, create microscopic electric currents, which generate magnetic fields (cm. Oersted’s discovery). Adding the magnetic fields induced by all the electrons of the atom, we get the total magnetic field of the atom.
In most substances, the magnetic fields of atoms are oriented randomly, as a result of which they are mutually quenched. However, in some substances and materials (primarily in alloys containing iron, nickel or cobalt), the atoms are ordered so that their magnetic fields are directed in one direction and reinforce each other. As a result, a piece of such a substance is surrounded by a magnetic field. Of these substances called ferromagnets, since they usually contain iron, and receive permanent magnets…
To understand how ferromagnets are formed, imagine a piece of hot iron. Due to the high temperature, the atoms in it move very quickly and chaotically, leaving no room for ordering atomic magnetic fields in one direction. However, as the temperature decreases, the thermal motion weakens and other effects begin to prevail. In iron (and some other metals), a force acts at the atomic level that tends to unite the magnetic dipoles of neighboring atoms with each other.
This force of interatomic interaction, called exchange force, was first described by Werner Heisenberg (cm. Heisenberg Uncertainty Principle). It is due to the fact that two neighboring atoms can exchange external electrons, and these electrons begin to belong simultaneously to both atoms. The exchange force firmly binds the atoms in the crystal lattice of the metal and makes their magnetic fields parallel and directed in one direction. As a result, the ordered magnetic fields of neighboring atoms are mutually reinforced rather than quenched. And this effect can be observed in the volume of a substance of the order of 1 mm.3containing up to 10sixteen atoms. Atoms of such magnetic domain (cm. below) are arranged in such a way that we have a pure magnetic field.
At high temperatures, the action of this force is hampered by the thermal motion of atoms, while at low temperatures, atomic magnetic fields can reinforce each other. The temperature at which this transition occurs is called Curie point metal – in honor of the French physicist Pierre Curie who discovered it.
In reality, the structure of ferromagnets is much more complex than described above. Typically, individual domains include only a few thousand atoms, the magnetic fields of which are unidirectional; however, the fields of different domains are directed randomly and in the aggregate, the material is not magnetized. Therefore, an ordinary piece of iron does not exhibit magnetic properties. However, under certain conditions, the magnetic fields of the domains that make up the ferromagnet are also ordered (for example, when hot iron is cooled in a strong magnetic field). And then we get a permanent magnet. The presence of the Curie point also explains why, when a permanent magnet is strongly heated, at some point, its complete demagnetization.