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The profound answer to the question How permanent magnets work? starts with

Sub-atomic particles such as electrons, protons, and neutrons (and many others) have a fundamental quantity called a spin angular moment. For an electron it is $ℏ/2$. This spin gives rise to a small magnetic moment for the electron. Despite the name, we don't think the electrons (or other particles) are spinning around an axis ... Every bound electron in an atom also "orbits" the nucleus. And this orbital motion gives it an orbital angular moment which also gives rise to the orbital magnetic moment.

This suggested, that a magnetic moment arises due to a circular movement and due to a spin. Nothing rotates due to the spin of the electrons, but it generates a magnetic moment.

What surprises me is why the accent is often on the spin of the electrons,

The spin is understood to be a fundamental property like mass or charge

but not on the intrinsic property of the magnetic moment of the electrons.

It seems to me that the order of discovery has a important influence on the primary and secondary role of spin and magnetic dipole moment:

  • Ampère's circuital law was discovered in 1823

  • Maxwell's explanation about the magnetic field as the result of moving charges was developed in the 1860th

  • The reason for the induction of a magnetic field couldn't be explained in this years. Only in 1907 it was predicted that electrons have a magnetic dipole moments: "The idea of elementary magnets is due to Walter Ritz (1907) and Pierre Weiss."

Taking the magnetic moment as an intrinsic property and explaining the deflection in a magnetic field by the interaction of those fields, would this conflict with the theory of electromagnetism?

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  • $\begingroup$ Please bear in mind that it is always underlined, the spin is nothing that rotates. It follows, that the deflection of electrons in an external field is not explainable with a rotation. / The magnetic dipole moment and the spin are always parallel respectively anti-parallel (the sign is a convention, but it holds for electrons and anti-protons, and for positrons and protons). Seems, that a synonymous use will be complicate due the unusualness, but at the end it would not change any physical law. This I’m thinking especially about Paulis exclusion principle and the four quantum numbers. $\endgroup$ – HolgerFiedler Jun 29 at 16:29
  • $\begingroup$ The emphatic statement that nothing rotates in the case of spin is remarkable. In every physical sense electron spin behaves as an angular moment. The correct statement is that we do not have a model of the electron in which rotation produces spin angular moment. $\endgroup$ – my2cts Jun 29 at 16:38
  • $\begingroup$ What is your definition of an “intrinsic property”? $\endgroup$ – G. Smith Jun 29 at 16:49
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    $\begingroup$ Are you aware that the electron’s spin is much “simpler” than its magnetic moment? Calculating its magnetic moment accurately is very complicated. $\endgroup$ – G. Smith Jun 29 at 16:51
  • $\begingroup$ Please keep comments focused on improving/clarifying the question and try to avoid discussion in them. Thanks! $\endgroup$ – tpg2114 Jul 3 at 19:33

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