Mercury is not magnetic in the way most people mean when they ask the question. It is diamagnetic, which means it is very slightly repelled by a strong magnet rather than attracted to one. If you hold a powerful magnet next to a puddle of liquid mercury, you will not see the metal leap toward it the way iron filings do. The repulsive force is so feeble that you would need sensitive instruments to detect it at all. Yet mercury’s relationship with magnetism turns out to be far richer than that flat “no” suggests, stretching from fusion reactor engineering to the first discovery of superconductivity.
Why Mercury Does Not Stick to a Magnet
Magnetic behavior in metals comes down to how their electrons are arranged. Iron, nickel, and cobalt are ferromagnetic because they have unpaired electrons whose tiny magnetic moments can line up cooperatively, creating a strong net field. Mercury has no such unpaired electrons available for that kind of teamwork. Every electron in a mercury atom is paired, so their individual magnetic moments cancel each other out almost perfectly. The leftover effect is diamagnetism, a universal but extremely weak tendency that all matter shares. In most substances diamagnetism is drowned out by stronger magnetic behavior, but in mercury nothing stronger is present to mask it.
In practical terms, diamagnetism in mercury is so weak that it has essentially zero everyday consequence. You could pour mercury over a magnet and the liquid would flow just as it would over a glass surface. No clinging, no visible deflection, nothing dramatic. That is the honest short answer for anyone wondering whether they can pick mercury up with a magnet or whether mercury will respond to a magnetic toy: it will not.
What Happens When You Force a Magnetic Field Through Liquid Mercury
Mercury may not be attracted to a magnet, but it is an excellent electrical conductor, and that fact changes everything when an external magnetic field is applied to mercury that is already flowing. When a conducting liquid moves through a magnetic field, the field induces electric currents in the liquid. Those currents then interact with the field to produce forces that resist the liquid’s motion. This phenomenon, called magnetohydrodynamic drag, is a real engineering concern in systems that pump liquid metals.
Researchers studying cooling systems for fusion reactors, for example, have measured the pressure drop that occurs when liquid mercury flows through a tube inside a powerful superconducting magnet. The drag can be substantial enough to complicate reactor cooling designs. One experimental program passed mercury through a helically coiled tube under a strong transverse magnetic field and found that the magnetohydrodynamic pressure drop was large enough to motivate the development of two-phase flow systems, where gas bubbles injected into the mercury stream reduce the effective drag.1Fusion Engineering and Design. Pressure drop and heat transfer of a mercury single-phase flow and an air–mercury two-phase flow in a helical tube under a strong magnetic field The point is that mercury can absolutely be pushed around by a magnetic field, just not by the simple attraction or repulsion that we associate with putting a magnet on a refrigerator.
This same principle works in reverse. If you run an electric current through mercury while it sits in a magnetic field, you generate a Lorentz force that can shove the mercury in a specific direction. Engineers have built miniature pumps that exploit this. In one design, tiny mercury droplets sit inside microchannels and are driven back and forth by an electromagnetic force, created by passing current through the conductive mercury in the presence of a magnetic field. The reciprocating droplets then push a non-conductive working fluid through a main channel, acting as pistons in a microscale pump.2Sensors and Actuators A: Physical. The effect of droplet size, channel length and the amount of electromagnetic actuation force on reciprocating movement of mercury droplets in the magneto mercury reciprocating (MMR) micropumps Mercury itself is not magnetic, but its electrical conductivity lets magnetic fields act on it indirectly, and that is enough to make it useful in electromagnetic devices.
Making Mercury Magnetic on Purpose
There is a way to make mercury genuinely magnetic, but it requires adding magnetic particles to it. A ferrofluid is a suspension of tiny magnetic particles in a carrier liquid. Most ferrofluids use oil as the carrier, but researchers have created mercury-based versions by dispersing nanoscale iron particles into liquid mercury. One method uses sodium amalgam to chemically reduce iron into the mercury while stirring it both mechanically and with a magnetic stirrer. The result is a liquid metal that responds to magnets, combining mercury’s conductivity and fluidity with actual magnetic attraction.3Journal of Applied Physics. The application of sodium amalgam to prepare ferrofluids containing iron particles in mercury
The magnetization of these mercury ferrofluids depends on the size and concentration of the suspended iron particles. Measurements of how the magnetization changes with field strength allow researchers to map the particle size distribution. The sodium left over from the amalgam reduction process actually helps stabilize the suspension, keeping the iron particles from clumping together and settling out.3Journal of Applied Physics. The application of sodium amalgam to prepare ferrofluids containing iron particles in mercury Over time, these samples do age, and the particle distribution shifts, but freshly prepared samples from the sodium amalgam method closely resemble those made by other techniques.
Why bother? A magnetically responsive liquid metal could be useful in seals, sensors, and actuators where you need a fluid that conducts electricity and can be precisely positioned with a magnet. The broader field of “magnetic liquid metals” has grown to include gallium-based alloys and other low-melting-point metals doped with magnetic particles, but mercury-based ferrofluids were among the earlier demonstrations that the concept works.
Mercury and Superconductivity
Mercury holds a special place in the history of magnetism and electrical physics: it was the very first superconductor ever discovered. In 1911, the Dutch physicist Heike Kamerlingh Onnes cooled mercury to just a few degrees above absolute zero and found that its electrical resistance vanished completely. Superconductors are famous for their magnetic properties. A superconducting material expels magnetic fields from its interior, a behavior called the Meissner effect. So at extremely low temperatures, mercury actually does have a dramatic magnetic response, but it is the opposite of attraction: the material actively pushes magnetic flux lines out of itself.
Mercury exists in more than one crystalline form when frozen, and both the alpha and beta crystal structures exhibit superconductivity, though at slightly different critical temperatures.4Physical Review. Superconductivity of α- and β-Mercury At room temperature and in its familiar liquid state, none of this matters. Mercury is just a weakly diamagnetic liquid. But the superconductivity story is a reminder that magnetic behavior is not a fixed property of a substance; it can change radically with temperature and physical state.
Nuclear Magnetic Resonance in Mercury
Even though mercury as a bulk material is not usefully magnetic, its atomic nuclei tell a different story. Certain mercury isotopes have a nuclear spin, which means their nuclei act like tiny magnets. When placed in an external magnetic field and hit with the right radio-frequency pulse, these nuclei absorb and re-emit energy at characteristic frequencies. This is the basis of nuclear magnetic resonance, the same physical phenomenon behind MRI machines in hospitals, though MRI typically works with hydrogen nuclei rather than mercury.
Researchers have made precise measurements of the resonance frequencies of two mercury isotopes, Hg-199 and Hg-201, in metallic mercury.5Journal of Physics and Chemistry of Solids. Isotope effect of nuclear magnetic resonances in metallic mercury The difference between isotopes is subtle but measurable, and it reveals information about the electronic environment surrounding the nucleus inside the metal. Mercury NMR has become a useful tool in chemistry for studying mercury-containing compounds and the way mercury atoms bond to other elements. For the average person, the takeaway is that “magnetic” at the nuclear level is a real phenomenon in mercury, but it operates on a scale far too small to make the metal stick to a magnet on your desk.
Mercury Vapor in a Magnetic Field
Mercury’s interaction with magnetism extends into optics. Mercury vapor lamps produce ultraviolet light at a characteristic wavelength of about 254 nanometers, and the behavior of that light changes when you apply a magnetic field to the vapor. Experiments with isotopically pure mercury vapor have shown that the way the vapor scatters resonance radiation shifts depending on the strength of the applied field. In weak fields, certain spectral features shift to lower field strengths as the optical density of the vapor increases, and in stronger fields the features shift the opposite direction.6Journal of Physics B. Forward scattering of resonance radiation by mercury vapour in a magnetic field
These effects are interesting to atomic physicists because they reveal how the energy levels of mercury atoms respond to external fields. For the rest of us, the practical legacy is that mercury vapor and magnetic fields together have been used in precision spectroscopy, atomic clocks, and magnetometry. The mercury atom’s sensitivity to magnetic fields at the quantum level is well established and technologically valuable, even though the bulk liquid metal does not behave like a magnet.
Mercury on Other Stars
One of the more surprising places where mercury and magnetism intersect is in astrophysics. A class of peculiar stars known as HgMn stars are chemically peculiar B-type stars that show unusually high concentrations of mercury and manganese in their atmospheres. For years, these stars were thought to lack significant magnetic fields, setting them apart from other chemically peculiar stars where strong fields are the norm. Recent spectropolarimetric work has complicated that picture. Careful measurements have revealed weak longitudinal magnetic fields, quadratic magnetic fields, and other magnetic signatures on the surfaces of several HgMn stars.7Astronomy & Astrophysics. Magnetic fields of HgMn stars
The analysis suggests that the strength of these magnetic fields correlates with the abundance anomalies of various elements and even with the binary properties of the star systems.7Astronomy & Astrophysics. Magnetic fields of HgMn stars In other words, the amount of mercury concentrated in a star’s atmosphere and the magnetic field at its surface are not independent. The mechanisms that sort elements in stellar atmospheres, like radiative levitation, interact with magnetic fields in ways that researchers are still working out. It is a long way from asking whether a magnet sticks to a bead of mercury on a lab bench, but it shows that the relationship between mercury and magnetism is a live question even in stellar physics.
Common Misconceptions Worth Clearing Up
A few misunderstandings come up repeatedly when people ask about mercury and magnetism. The first is confusing the element mercury with the planet Mercury, which has its own weak but real magnetic field generated by a partially molten iron core. The planet’s magnetism has nothing to do with the element’s magnetic properties; they just share a name.
The second is the idea that because mercury is a metal, it should be attracted to magnets. Most metals are not ferromagnetic. Aluminum, copper, lead, gold, silver, and tin are all non-ferromagnetic. Iron, nickel, and cobalt are the exceptions among everyday metals, not the rule. Mercury is in good company as a metal that a magnet will not pick up.
A third misconception is that liquid metals in general are magnetically inert and uninteresting. As the ferrofluid research and magnetohydrodynamic experiments show, liquid metals can be manipulated, pumped, and even magnetized using external fields and clever engineering. The liquid state actually opens up possibilities that solid metals do not offer, because the material can flow and deform in response to forces. Mercury was one of the first liquid metals explored for these purposes, and while gallium-based alloys have taken over much of the applied research because of their lower toxicity, mercury-based work laid important groundwork.
Why Liquid Mercury Stays Liquid and What That Means for Magnetism
Mercury’s status as the only metal that is liquid at room temperature is itself connected to the same physics that makes it weakly diamagnetic. The electrons in mercury atoms are moving at a significant fraction of the speed of light, which causes relativistic effects that contract the inner electron shells and weaken the bonds between mercury atoms. The result is a metal with an unusually low melting point: about minus 39 degrees Celsius, so it is liquid well below room temperature. Those tightly bound, fully paired electrons are also the reason mercury has no unpaired spins available to produce paramagnetism or ferromagnetism. The same physics that keeps mercury liquid keeps it magnetically bland in its bulk form.
This connection means there is no realistic way to change mercury’s fundamental magnetic character without changing its composition. You cannot magnetize pure liquid mercury by chilling it (unless you chill it far enough to reach superconducting temperatures, which requires getting close to absolute zero). You cannot magnetize it by running current through it, though you can exert forces on it that way. And you cannot magnetize it by exposing it to even very strong magnets. The only route to a genuinely magnetic mercury-based liquid is to mix in magnetic particles, as in the ferrofluid approach, which makes the final product a composite rather than pure mercury.
For anyone handling mercury in a practical context, whether cleaning up a broken thermometer or working with it in a laboratory, the takeaway is straightforward: a magnet is not a useful tool for collecting or controlling liquid mercury. Specialized mercury spill kits use chemical methods and fine-tipped suction tools instead. The element’s relationship with magnetism is scientifically rich and technologically exploitable, but at the everyday human scale, mercury and magnets simply do not interact in a way you can see or feel.