Magnetism of Mercury
Most recent answer: 10/22/2007
Many compounds containing mercury are also weak diamagnets, but some are a little stronger than mercury itself. It probably is possible to make an alloy of iron and mercury which is magnetizable, but that wouldnt be the mercurys doing.
Mercury is much more interesting magnetically at very low temperatures. At temperatures below about 4 degrees Kelvin, elemental mercury becomes a superconductor. In fact, superconductivity was discovered by Kamerlingh Onnes in 1911 by studying mercury at low temperatures.
Superconductors generally expel magnetic fields, so you could say that below 4 K, mercury is a perfect diamagnet. To expel a magnetic field from a material, a canceling field must be created by that material with currents flowing on the surface. These currents flow with no resistance in superconductors.
You can also make a permanent magnet out of a loop of superconducting mercury. Simply cool down a loop of mercury in an external magnetic field (the temperature at which the mercury will superconduct will get lower as the applied field gets stronger). After the mercury becomes superconducting, it locks in the total magnetic flux through the loop. Switch off the external magnetic field, and a persistent current will flow around the mercury loop, making a permanent magnetic field.
(published on 10/22/2007)
Follow-Up #1: When superconducting magnets go normal
- Bruce W. (age 28)
Clearlake Califonia USA
I think that pretty much covers it.
(published on 07/21/2012)
Follow-Up #2: cooling superconductor in field
- Bruce W. (age 28)
Clearlake Ca USA
Now an exception comes up if there's something else trapping the field in the region of the mercury. An external superconducting cylinder would be one example. Then re-cooling the mercury will capture some field again. The field inside the mercury ring will go up just slightly, because the field that had penetrated the mercury will partly be pushed inside the ring and partly outside the ring.
(published on 07/23/2012)
Follow-Up #3: magnetic panning for gold with mercury
- Robert Way (age 55)
Now there's another possible mechanism. Gold and mercury are conductors. That means that changing magnetic fields stir up eddy currents in them. That gives them temporary magnetic moments. If this is how you're moving them, I'd predict that if you tried moving the magnet slowly, it wouldn't work, since it's the rate of change of the field that counts.
But why would nothing happen without the mercury? Two reasons:
1. The mercury helps form bigger blobs of conducting metal, allowing for more eddy currents.
2. The mercury can lubricate things, reducing friction.
Try the slow-motion experiment and let us know how it comes out.
(published on 10/16/2012)
Follow-Up #4: superconducting levitation
- derek (age 36)
cornelius oregon USA
It's hard to follow the description of where the currents are flowing, but we can answer your more general question. Mercury will go superconducting when it's cold enough, and superconductors can be used to levitate magnets or other superconductors.
(published on 11/30/2016)