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I have read this question:

However, in a small number of solids the outermost electrons of the atoms line up parallel with each other and their magnetic moments reinforce each other to give the solid a large net magnetic moment. These solids interact strongly with magnets, and we call them ferromagnetic. Only solids having unpaired electrons can be ferromagnetic, but only a small fraction of these solids are actually ferromagnetic. Non-ferromagnets may be diamagnetic or paramagnetic. However these interactions are several orders of magnitude weaker than ferromagnetism and the interaction is too weak to be measured outside a laboratory.

Why does magnet attract iron but not other metals?

And this video:

enter image description here

https://www.youtube.com/watch?v=wtdnByoSPgw

Now as far as I understand, an object needs to have unpaired electrons in the outer shell to be repelled or attracted by a magnet, and though it may be only mentioned for solids, and especially crystallines (with a microcrystalline structure), water might be diamagnetic.

If all electrons in the particle are paired, then the substance made of this particle is diamagnetic If a powerful magnet (such as a supermagnet) is covered with a layer of water (that is thin compared to the diameter of the magnet) then the field of the magnet significantly repels the water. This causes a slight dimple in the water's surface that may be seen by a reflection in its surface.[8][9]

https://en.wikipedia.org/wiki/Diamagnetism#Curving_water_surfaces

You can't derive the existence or magnitude of diamagnetic properties just from unpaired electrons. On the contrary, diamagnetism mostly comes from the complete shells. They behave as electric current loops that orient themselves in a certain way in the external magnetic field. Copper has lots of these complete shells, so the diamagnetic contribution is large. There's also the opposite contribution from the unpaired electron but it's just one electron and the paramagnetic contributions "scale" with the number of these electrons and one is too few. So the diamagnetic terms win.

Why is copper diamagnetic?

Now all of these explanations on this site talk about solids, and none of them explain anything about liquids being diamagnetic. The best explanation comes from Lubos Motl, saying that diamagnetism comes from complete shells, acting as current loops that orient themselves in a certain way in the external magnetic field. This is a very clear and nice explanation in the case of solids, that have crystalline microstructures, and where the structure is rigid in terms of molecules not being able to rotate or move relative to each other, creating current loops that orient themselves aligned.

Though, I am very curious as to how this would work in the case of a liquid like water, because water molecules are loosely bound by the Van der Vaals force, but can and do roll over each other, making water able to reform itself in certain cases where force is applied. Just like in a magnetic field, the water molecules do not organize themselves into a rigid crystalline structure, but rather are loose. The current loops of the complete shells thus would be randomly changing their alignment in the magnetic field (become misaligned, thus cancel). All the explanations state that diamagnetism is very weak and can hardly be detected in everyday experiments. Then how can the magnet in the video push the tube of water?

Question:

  1. Can magnets really repel water (liquids) like this?
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    $\begingroup$ The key point is the strength of the magnet, you won't see this with a standard refrigerator magnet. $\endgroup$
    – Triatticus
    Commented Jan 7, 2022 at 0:08
  • $\begingroup$ Google for "levitating frog." $\endgroup$ Commented Jan 7, 2022 at 1:49

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It is energetically favourable for diamagnetic moments to anti-align with an applied $B$ field.

In a liquid all these microscopic moments are free to rotate (subject to thermal fluctuations) and as such all anti-align with the applied field.

An example of magnetic moments rotating in a fluid is in the "super paramagnetic" ferrofluid (except here the ferromagnetic nanoparticles align with the $B$ field).

For further reading I recommend "Magnetism and Magnetic Materials" by Coey.

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