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Elementary magnets
To illustrate the magnetization of ferromagnetic materials such as iron, the German physicist Wilhelm Weber designed a special explanatory model in the 19th century. This model sketched the magnetic effect visually with the help of many small elementary magnets (comparable to tiny bar magnets), which should only generate an externally measurable magnetic field by common alignment in the same direction. The fact that certain atoms actually behave like elementary magnets thanks to their magnetic dipole moment was discovered much later.
From today's point of view, what is an elemental magnet?
For the explanation of magnetic units physics has retained the concept of elementary magnets. They are realized as atoms in a grid. Each of these atoms has electron orbitals (based on the probability of electron residence in the atom), which in turn contain a specific spin. This spin is ultimately responsible for magnetism.
The arrangement of elementary magnets plays a special role in relation to the behavior of the magnetic field. If they are all aligned in different directions, the magnetic fields of the individual elementary magnets cancel each other out and the body contains no magnetic force. On the other hand, if the elementary magnets all point in a common direction, one can measure a magnetic field. The body is then magnetized. But how can elemental magnets be influenced?
How do elementary magnets align?
There are different starting possibilities that affect elementary magnets. By introducing an external magnetic field, the elementary magnets align in parallel and then amplify the external field (paramagnetism). If the elemental magnets themselves have common directional tendencies, sometimes spontaneous complete alignment occurs in special areas, the Weißsche districts. This reaction can be even stronger with a ferromagnet by an external magnetic field (Exchange interaction). Even after switching off the outer field remains a remanence left, which is lost only by heating (Curie temperature) or vibration. Since the magnetic properties of matter are due to the elementary magnets, the operation of many devices within the research based on this view - so, for example, in the magnetic resonance tomography.