Magnetic moment

The magnetic moment is a vector that is perpendicular to the surface around which current flows and whose arrowhead points away from the north pole. Accordingly, the field lines run closed from the north pole to the south pole and then in the conductor loop parallel to the magnetic moment back to the north pole (see illustration).

As there are no magnetic fields with only one pole (monopoles), the simplest magnetic moment is a so-called dipole moment. It always has two opposite poles. Electric fields, on the other hand, can also have a monopole moment. This is the field that emanates from a single-point charge. In contrast, two charges at a fixed distance form an electric dipole moment similar to magnetism. (see illustration)

The magnetic effect of permanent magnets is also explained by circular currents in the material. It is assumed that the electrons have an electron spin from which a magnetic moment emanates. During magnetisation, all these magnetic moments are aligned in parallel. This is also referred to as magnetic magnetic polarisation. In ferromagnetic materials, this leads to permanent magnetisation if the alignment is sufficiently strong. The magnetic polarisation does not disappear when the external magnetic field is turned off. The remaining magnetic polarisation is also called remanence. The magnetic moments of all electron spins were aligned in parallel and resulted in a macroscopic magnetisation, which is created by the sum of all magnetic moments of the electron spins.

The reason for the permanent alignment is the exchange interaction between all magnetic moments of the electron spins. This exchange interaction stabilises the aligned electron spins with each other, and remanence occurs. The alignment of the magnetic moments can be disturbed by the addition of heat, which promotes the movement of the electrons and thus the rearrangement of the magnetic moments of the electron spins. Striking a permanent magnet hard will also ruin the magnetisation. Lastly, the magnetisation can be destroyed by an opposing field of coercivity because the opposing field exerts a force on the magnetic moments of the aligned electron spins that attempts to rotate the magnetic moments in the opposite direction.