I've learned that magnetic fields are generated by electric currents, and that electric current is the motion of electrons and stuff like that. Many textbooks also talk about "point charges" and have diagrams like these:

https://i0.wp.com/buphy.bu.edu/~duffy/PY106/2e.GIF http://web.mit.edu/8.02t/www/802TEAL3D/visualizations/guidedtour/Tour_files/image135.jpg
(source: mit.edu)

But I can't remember any time where an experiment was mentioned that demonstrates magnetism between two atoms or at the quantum level. Are there any such experiments? If so, what does magnetism look like at that level? If not, why not?

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    $\begingroup$ Search terms: fine structure; hyper-fine structure; quantum hall effect; SQUIDs; etc. $\endgroup$ – dmckee Sep 17 '14 at 2:56
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    $\begingroup$ Every permanent magnet is magnetism on the atomic level... multiplied by the number of atoms in the magnet. The magnetic interaction between single atoms can be measured with a magnetic force microscope: en.wikipedia.org/wiki/Magnetic_force_microscope. $\endgroup$ – CuriousOne Sep 17 '14 at 6:31

Yes, experiments involving magnetism at the quantum level have been performed. For example, precise measurements involving the spin magnetic moment of an electron have established that the anomalous magnetic dipole moment predicted by quantum electrodynamics is correct. The experiments involved are among the most precise experiments ever performed; see the Anomalous magnetic dipole moments section of the Precision tests of QED Wikipedia article.

Spin magnetic moments also create a basis for the Pauli exclusion principle, and explain hyperfine splitting, both of which are well-established experimentally.

  • $\begingroup$ Could you please argue about the spin magnetic moment/Pauli principle relation? $\endgroup$ – Py-ser Sep 17 '14 at 3:12
  • $\begingroup$ @Py-ser I basically just echoed a statement in Wikipedia at en.wikipedia.org/wiki/Spin_magnetic_moment#Spin_in_chemistry , which unfortunately doesn't cite a source that I could direct you to. $\endgroup$ – Red Act Sep 17 '14 at 3:46

Phenomena such a paramagnetism and ferromagnetism cannot be explained using classical statistical mechanics. This is called the Bohr-van Leeuwen theorem. An explanation of these phenomena need us to invoke quantum mechanical ideas such as spin.


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