The magnetic moment of an atom is the main physical vector quantity that characterizes the magnetic properties of any substance. The source of the formation of magnetism, according to the classical electromagnetic theory, are microcurrents arising from the movement of an electron in orbit. The magnetic moment is an indispensable property of all elementary particles, nuclei, atomic electron shells and molecules without exception.
Magnetism, which is inherent in all elementary particles, according to quantum mechanics, is due to the presence of a mechanical moment in them, called spin (its own mechanical momentum of quantum nature). The magnetic properties of the atomic nucleus are made up of the spin impulses of the constituent parts of the nucleus - protons and neutrons. Electronic shells (intraatomic orbits) also have a magnetic moment, which is the sum of the magnetic moments of the electrons located on it.
In other words, the magnetic moments of elementaryparticles and atomic orbitals are due to an intra-atomic quantum mechanical effect known as spin momentum. This effect is similar to the angular momentum of rotation about its own central axis. Spin momentum is measured in Planck's constant, the fundamental constant of quantum theory.
All neutrons, electrons and protons, of which, in fact, the atom consists, according to Planck, have a spin equal to ½. In the structure of an atom, electrons, rotating around the nucleus, in addition to the spin momentum, also have an orbital angular momentum. The nucleus, although it occupies a static position, also has an angular momentum, which is created by the nuclear spin effect.
The magnetic field that generates an atomic magnetic moment is determined by the various forms of this angular momentum. The most noticeable contribution to the creation of a magnetic field is made by the spin effect. According to the Pauli principle, according to which two identical electrons cannot be simultaneously in the same quantum state, bound electrons merge, while their spin momenta acquire diametrically opposite projections. In this case, the magnetic moment of the electron is reduced, which reduces the magnetic properties of the entire structure. In some elements that have an even number of electrons, this moment decreases to zero, and the substances cease to have magnetic properties. Thus, the magnetic moment of individual elementary particles has a direct impact on the magnetic qualities of the entire nuclear-atomic system.
Ferromagnetic elements with an odd number of electrons will always have non-zero magnetism due to the unpaired electron. In such elements, neighboring orbitals overlap, and all spin moments of unpaired electrons take the same orientation in space, which leads to the achievement of the lowest energy state. This process is called exchange interaction.
With this alignment of the magnetic moments of ferromagnetic atoms, a magnetic field arises. And paramagnetic elements, consisting of atoms with disoriented magnetic moments, do not have their own magnetic field. But if you act on them with an external source of magnetism, then the magnetic moments of the atoms will even out, and these elements will also acquire magnetic properties.
