# What does the magnetic moment of a quantum particle depend on?

Every magnetic object has a magnetic moment. From electrons to molecules, to even planets. But my question is, what determines the magnitude of a magnetic moment a quantum object has? Does the magnitude of the magnetic moment of a quantum particle depend on mass, charge, ect? Or is it just an intrinsic property that a particle has, and is not dependent on anything?

This is really two questions, one on leptons and one on quarks .Some moments of particles are listed in Magnetic Dipole Moments.

Does the magnitude of the magnetic moment of a quantum particle depend on mass, charge, ect? Or is it just an intrinsic property that a particle has, and is not dependent on anything?

The magnetic moment of a lepton, such as an electron, is intrinsic, and related to spin, but for composite particles such as mesons ( a quark and an antiquark), and baryons (three quarks ), I would refer you to this answer Magnetic Moments, which points out that simple addition of individual magnetic moments of quarks is not applicable. So the magnetic moment of an up quark, is not $\mu_p = \frac{4}{3}\mu_u - \frac{1}{3}\mu_d$, for example.

For baryons, there are 3 valance quarks, but at any one time other quarks may exist, which complicates the issue of individual quarks.

• So for all elementary particles, the magnetic moment is just an innate property? – Jag Mar 22 '17 at 21:46
• First, I apologise because you don't actually ask a list question. For leptons yes, and for quarks, I would guess yes, but I would ask you to read this en.m.wikipedia.org/wiki/Neutron_magnetic_moment, as quarks don't and can't exist individually, so they are not as easy to describe or measure. I am implicitly not counting protons, neutrons etc as elementary. But I hope you get an answer from a more informed source – user146020 Mar 22 '17 at 21:54
• Countto10 "The magnetic moment of ... an electron, is intrinsic, and related to spin". Isn't the spin only a synonym for the existence of a magnetic dipole moment and its direction? – HolgerFiedler Mar 23 '17 at 6:43
• @HolgerFiedler Hi Holger, thanks for your comment. I can't add anything to Emilio's answer to your related question, both through ignorance on my part and because I think there is no other connection between quantum spin and classical spin other than the one listed here: Quantum Spin But I wonder if anyone is completely happy with our current understanding of the attribution of angular momentum to particles. It is, as I naively understand it, a semi-classical idea akin to Bohr's orbital theory and may eventually be discarded in the future – user146020 Mar 23 '17 at 11:02
• @Countto10 Thank you so much for support. Surprisingly I was able to approve your very welcome edits. – HolgerFiedler Mar 23 '17 at 20:54