Magnet FAQ

Before I try to answer, let's acknowledge that every answer not in terms of graduate-level physics is going to involve a certain amount of hand-waving. There's a very entertaining video of the legendary Richard Feynman explaining that he can't explain it to you in terms of what you already know, and I am not under the illusion of having exceeded Dr. Feynman in my explanatory prowess. So, at some level, I will always disappoint the Juggalos out there. But here's my best shot at it:

When electricity moves, it leaves electric and magnetic fields in its wake. Since every electron is spinning, that means it creates a magnetic field. In most atoms, the electrons pair off so their spin cancels out. In iron, they space out so that their spins don't automatically cancel out. When a magnetic field gets applied, it can get all of those spins to point the same way, making a magnet. A permanent magnet locks all of those spins in once you get them organized.

I have absolutely glossed over a bunch of fascinating concepts like Maxwell's Equations, Schrödinger's Wave Equation, and orbital hybridization because it's outside the scope of an FAQ, but that's as honest an answer as I can give without "cheating you," as Dr. Feynman described it.

Short version: Magnets are weird, but also useful. Like me.

Magnets don't do work — you do work. It takes no energy to hold something still: a magnet holding a wrench to a wall is doing exactly what a hook does, exerting a force with no motion, and force without motion is not work. The hook doesn't run down and neither does the magnet.

Energy changes hands only when things move, and it's your energy. When you bring the wrench close and it snaps onto the magnet, that's like dropping it on the floor. When you pull it away, that's like picking it up. The magnetic field is like the gravity field — it's just the thing you do work against. Nothing was created; it was stored in the arrangement of magnet and wrench and returned when you separated them.

That is also why a "magnet motor" can't run on its own. A permanent magnet's field is fixed in space. Move anything around a closed loop in a fixed field and the net work is exactly zero: whatever the field gave you on the way in, it takes back on the way out. Magnets are extraordinary at converting energy — that's what a motor does — but they are not a source of it.

Mostly no, but also yes. For all intents and purposes, permanent magnets are indeed permanent until you do something to them. Left alone at room temperature, a sintered neodymium magnet loses a fraction of a percent of its strength over the first years as the least stable domains relax, then essentially stops. Ferrite and samarium-cobalt are more stable still.

That "something" comes in three forms: heating it up, applying a demagnetizing field, or chemically breaking it down. Heat above the grade's rated operating temperature weakens it first temporarily and then permanently. A strong opposing field — another magnet forced pole-to-pole, or a large electromagnet — can partially demagnetize it, which is why alnico magnets were shipped with keepers and why motor designers check the demagnetization curve. And corrosion or physical damage: neodymium magnets are mostly iron and are brittle, so a rusted or chipped magnet has simply lost volume.

A magnet that has been weakened by heat or an opposing field can usually be fully remagnetized in a pulse magnetizer, as long as the material itself is intact. Magnets don't "run out." They can be knocked down, and they can be set back up.

This is another question that takes a deep dive into graduate-school science to answer properly. The short form is that it has to do with the way atoms bond. What's unique about iron, cobalt and nickel — the first d-row elements on the chart — is that they have relatively few ways they can bond, so their unpaired electrons are left with little choice but to line up with their neighbors. As you go down the chart, electron structures get more complicated, which offers more ways to avoid magnetism (which is nature's preferred state). Aluminum, copper and silver have their electrons either paired off or free to roam, so they respond to a magnet only very faintly, and a hand-held magnet will not stick to them. Gadolinium is ferromagnetic too, but only below about 20 °C.

That said, the more complex electron structures can also be very useful, which is how the rare earths joined the party — more on that under neodymium below.

Stainless steel is the confusing case because "stainless" is a family. The common austenitic grades — 304 and 316, used for sinks, countertops and cookware — have enough nickel to lock the iron into a crystal structure that isn't ferromagnetic, so a magnet slides off. Ferritic and martensitic grades — 430, and the hardened steels in knives — keep iron's normal structure and a magnet sticks firmly. Cold-working a 304 part (bending, stamping) can convert some of it and make it slightly magnetic, which is why a magnet sometimes grabs the corners of a "non-magnetic" sink.

You get two complete magnets, each with a north and a south pole. Cut those in half and you get four. Keep going and you eventually reach a single atom, which is still a dipole — a north and south with nothing between them.

That's because a magnet's poles aren't things attached at the ends; they are the two faces of one circulation. Every magnetic field is a closed loop, leaving at north and returning at south, and there is no way to cut a loop so that only one end remains. Physicists have looked hard for a genuine "monopole" — an isolated north — and have never found one. Every magnet ever made has two poles, and suppliers who receive the request for a one-pole magnet politely decline.

The practical consequence: a sliced magnet is weaker, not because you lost magnetism, but because each half is now a shorter magnet with more of its own field working against itself.

Ironically, in my day job, we do exactly this. The trick is in the question: it should really be "why can't I make a magnet that isn't moving float?"

Try to balance one magnet above another with repulsion alone and it will always slide off sideways or flip over. That isn't bad luck — it's a theorem. Earnshaw showed in 1842 that no arrangement of permanent magnets can hold another magnet stably in mid-air; there is always at least one direction in which a tiny nudge grows instead of correcting.

Every levitation you've seen gets around the theorem by adding motion, control, or a material that isn't a permanent magnet. The floating globe on a desk uses an electromagnet with a sensor that adjusts the current thousands of times a second. The spinning-top toy stays up only while it spins. A magnet floating over a superconductor works because the superconductor isn't a permanent magnet — it actively pushes back against any change. Pyrolytic graphite floats because it is diamagnetic, and Earnshaw's theorem has a loophole for diamagnets. Most commercial maglev trains use controlled electromagnets in a feedback loop, the same as the desk globe, only much larger.

If you only want the effect of levitation, a single point of contact — a pencil tip touching a plate — is allowed, and that is how most "levitating pen" desk toys work.

Nothing blocks a magnetic field the way a wall blocks light; the field passes through wood, plastic, glass, aluminum, water and your hand without noticing. What you can do is give it an easier path. A sheet of steel or a nickel-iron alloy carries flux far more willingly than air, so field lines crowd into the sheet and around whatever is behind it. That is shielding — redirecting, not stopping — and it is why a steel case protects a compass and why a superconducting MRI magnet sits inside a room lined with steel.

One significant exception is a superconductor. Superconductors are perfect diamagnets: they reject a magnetic field entirely, and flux simply does not enter the material. This is a side effect of the extremely high charge-carrier mobility inside them — currents spring up on the surface to cancel any field that tries to get in. It is the closest thing to a true magnetic wall that exists, and it's the reason a magnet will hover over a cooled superconductor.

A magnet's reach has no sharp edge, but it falls off fast: for a small magnet the field drops roughly with the cube of the distance, so twice as far away is about one-eighth the field. In practice a magnet influences steel out to a distance comparable to its own size and is negligible beyond a few times that. A one-inch neodymium disc that could lift a wrench from contact will barely turn a compass needle from across the room.

Yes to both. Water is very nearly transparent to a static magnetic field, and a vacuum is perfectly so; a magnet is exactly as strong at the bottom of a lake or in orbit as on your desk. The practical issue underwater is corrosion, not magnetism: a neodymium magnet is mostly iron and will rust through a scratched coating in weeks, so marine applications use thicker plating, encapsulation, or ferrite and samarium-cobalt, which don't corrode.

Space adds a wrinkle at the extremes. Some sintered neodymium grades weaken if cooled far below −100 °C, and satellite designers pay attention to that. Praseodymium-iron-boron magnets don't suffer this effect, and are still used in some specialty cryogenic applications for exactly that reason. In ordinary conditions, though, cold makes a permanent magnet slightly stronger, not weaker.

Not in the sense of turning them into magnets. Magnetism at the strength you can feel needs unpaired electrons that agree to line up with their neighbors, and the atoms in wood, plastic and glass have their electrons fully paired. Those materials are actually very weakly repelled by a magnet — diamagnetism — but you need a field of several tesla to see it, which is how frogs and strawberries have been levitated in laboratory magnets.

What you can do is embed magnetic material in a non-magnetic one. A flexible fridge magnet is exactly that: ferrite powder in a rubber binder. "Bonded" neodymium magnets are the same idea with a stronger powder in nylon or epoxy, and they show up in small motors and sensors where a molded shape matters more than maximum strength. So a magnetic plastic exists — but it is a plastic full of magnet, not a magnetized plastic.

It's true: a lump of pure neodymium is not a magnet at room temperature. Neither is a lump of pure iron, in any useful sense — iron is easy to magnetize and just as easy to demagnetize, which is why a nail doesn't stay a magnet after you pull it off one.

A neodymium magnet is a compound, Nd₂Fe₁₄B, and the two metals do different jobs. Iron provides nearly all of the magnetism — there are fourteen iron atoms for every two of neodymium. Neodymium provides the discipline. Remember the complex electron structure of the rare earths from a few questions back: think of neodymium as an exceptionally good field marshal with tight control of his troops, the troops in this case being the iron atoms. Its inner electrons interact very strongly with the crystal around them and make the whole structure resist being turned: once magnetized along its preferred axis, it takes an enormous opposing field to flip it back. That resistance is called coercivity. What neodymium does really well is keep iron from demagnetizing — it doesn't make the iron more magnetic.

Iron alone gives you strength you can't keep. Neodymium and boron lock it in. That combination — the most flux of any commercial magnet, and enough coercivity to hold it in a thin disc — is why nearly every high-performance motor built today uses this material.

Among permanent magnets, sintered neodymium-iron-boron, and within that family the highest energy-product grades — N52 is the strongest widely sold, with N55 available from a few producers. An N52 magnet has a remanence around 1.45 tesla; the field you'd measure at the surface of a small disc is lower, typically 0.3 to 0.65 tesla depending on shape, because a magnet's field spreads out the moment it leaves the material.

"Strongest" for a buyer usually means pull force, and that depends far more on size than on grade. Stepping from N42 to N52 adds roughly twenty percent; doubling the volume adds far more. A two-inch N52 cube will hold several hundred pounds to a steel plate and is genuinely dangerous to handle.

Beyond permanent magnets: a clinical MRI runs at 1.5 or 3 tesla, resistive and superconducting research magnets reach about 45 tesla steady, and pulsed laboratory magnets briefly exceed 100 tesla. The strongest known magnets are magnetars — neutron stars with fields around a billion tesla — which are the reason "would a magnet pull the iron out of my blood" has a real answer: yes, but only at that scale.

Heat is a permanent magnet's natural enemy. Warming the magnet shakes the atoms and loosens their agreement to point the same way, so the field weakens — reversibly at first, and a neodymium magnet gets back what it lost when it cools. Every grade comes with a published maximum operating temperature — 80 °C for a standard neodymium grade, up to about 230 °C for the specialty grades, higher still for samarium-cobalt, ferrite and alnico. Read those as practical limits: the temperature above which the magnet starts to fail in most applications, because some domains flip for good and the magnet comes back weaker and in need of remagnetizing. How far you can actually push a given magnet depends on its shape and what it's working against, which is why the datasheet gives you a curve rather than a single number.

The Curie temperature is a different and higher figure: the point at which the material stops being ferromagnetic at all. For iron that's 770 °C; for neodymium magnets it is a few hundred degrees above the working limit, depending on grade. The gap between the two is why the "H," "SH" and "UH" grades exist — they don't move the Curie point much, but they hold their domains in line closer to it.

Melt a magnet and there is no magnetism left to speak of — a liquid has no crystal for domains to live in. Cool it back into a solid and it's just an unmagnetized lump until someone puts it in a magnetizer.

Earth's core is well above iron's Curie point, and it is not a permanent magnet. It's an electromagnet: the outer core is molten iron that conducts electricity and circulates, and moving conductor plus existing field generates current, which generates field. That self-sustaining loop is the geodynamo. The same distinction — permanent magnet versus electromagnet — is why a magnet's field can survive being frozen but not being melted, while the planet's can survive being hotter than a furnace.

For the same reason heat weakens them, run backwards. A magnet's field is the sum of countless atomic magnets that mostly agree on a direction; thermal motion is what keeps them from agreeing perfectly. Cool the magnet and the jitter dies down, alignment improves, and the field creeps up — about a tenth of a percent per degree for a neodymium magnet, more for ferrite.

There are limits. Some neodymium grades pass through a spin reorientation around −135 °C and start weakening again, and ferrite becomes easier to demagnetize when cold, so a cold ferrite motor magnet is more vulnerable, not less. For anything you would meet outside a laboratory, though, a cold magnet is a slightly stronger magnet.

The number is a rough estimate of the energy product of the magnet in megagauss-oersteds — how much magnetic energy the material packs per unit volume. For a one-number metric of how strong a magnet is, it's as good as any, and it's useful for explaining how strong a magnet is: N35 is the entry grade, N52 the strongest in general commerce, and a higher number means more field from the same size. The letters after the number — M, H, SH, UH, EH, AH — add some color by explaining how the magnet develops that energy product: a plain N grade gets there with maximum flux and modest coercivity and is rated to 80 °C, while the lettered grades trade a little flux for much more coercivity and hold up to about 230 °C. For what all of that means on a datasheet, see Reading a B-H curve.

Gauss is a unit of flux density; 10,000 gauss make one tesla. A magnet does not have a single gauss value. The datasheet figure, remanence, is the flux density inside the material (about 14,500 gauss for N52); the number a hand-held gaussmeter reads at the surface is much lower and depends on the magnet's shape, and neither one is what you'll measure an inch away.

Pull force is the force needed to pull the magnet straight off a thick, flat, clean mild-steel plate. It is a fair comparison between magnets and a poor predictor of what one will hold in real life. Thin sheet steel, paint, a slight air gap, or a load hanging in shear rather than straight pull each cut the figure sharply; a rule of thumb is that a magnet holds about a third of its rated pull in shear. Both poles are equally strong.

Yes, up to a point. Two identical discs stacked north-to-south behave like one magnet twice as thick, and a thicker magnet has a stronger and farther-reaching field at its face. But the returns shrink: once the stack is a few times longer than it is wide, the far end is too distant to help the near end, and adding more does almost nothing. If you need more pull at a surface, a wider magnet beats a taller stack.

Stacking side by side, poles alternating, does something different and often more useful: it concentrates the field close to the surface and makes it fall off quickly. That's how a fridge-magnet strip holds well yet doesn't reach through the door, and a more sophisticated version of the idea — the Halbach array — is how a phone's magnetic charger produces a strong grip at the back and almost no field toward the phone's electronics.

I got my start in magnetics figuring out how to erase floppy disks and hard drives, so this is one I know very well.

The warning was real once, and it was about three specific things: cathode-ray-tube screens, whose electron beam a magnet bends and whose steel frame it can permanently magnetize; floppy disks and tape, which store data as magnetic patterns a strong field can scramble; and older, low-coercivity magnetic stripes on cards. None of those is in your pocket anymore.

A modern phone stores data in flash memory, which is electrical, not magnetic, and is indifferent to a static field. Its screen is an LCD or OLED. Its processor doesn't care. The only part that does notice is the magnetometer — the compass — which will point the wrong way while a magnet is nearby and recover when it leaves; that's why the magnets in phone cases and chargers are arranged to keep their field local. Hotel key cards and the stripes on credit and debit cards are today mostly high-coercivity and shrug off a fridge magnet, though a large neodymium magnet held directly against them can still do damage, and a magnetic wallet clasp near an older stripe is asking for trouble.

Mechanical hard drives are more robust than their reputation — the platters are shielded and the read head is not easily disturbed. There's also a big difference between making a drive stop working and erasing the data on it. A powerful magnet held against the case can upset the head positioning or the drive's own motor magnets and make it misbehave; actually scrambling the bits on the platters takes a far stronger field applied much closer than a case allows, which is why degaussers are purpose-built machines and why the data on a "magnet-killed" drive is usually still recoverable by someone who wants it badly enough.

As a rule of thumb — not a law of physics — keep large magnets a hand's width away from anything with a spinning disc, a compass, or a stripe. Everything else in modern electronics is safe.

I sure hope not, because I have been around a lot of the world's very strongest magnets!

A static magnetic field, at any strength you can buy, has no established effect on the human body. The iron in your blood is not the iron in a nail: it sits one atom at a time inside hemoglobin, with no neighbors to line up with, so blood is not ferromagnetic and a magnet doesn't tug on it. You can prove this to yourself by holding a powerful neodymium magnet in your hand: you'll notice it doesn't leave a red patch where it pulled blood in — or, said differently, it didn't make you blush. Your nerves run on ion currents, not electrons in wires, and a steady field does not push them around. That is why an MRI, which puts you inside a field twenty thousand times Earth's for half an hour, is considered safe enough to repeat; the sensations people report in the strongest research magnets — dizziness, a metallic taste — come from moving through the field, and stop when they hold still. International guidelines set the general-public exposure limit at 0.4 tesla and the occupational limit at 2 tesla for the head and torso, and neither is remotely approached outside a laboratory or an MRI suite.

The real dangers of strong magnets are mechanical and specific. Two neodymium magnets snapping together will crush a finger between them and can shatter, throwing sharp fragments; wear eye protection with anything over an inch. Swallowed magnets are a genuine emergency — two of them can pinch bowel wall between them from opposite sides — and small high-power magnets should be kept away from children entirely. Anyone with a pacemaker or implanted defibrillator should keep strong magnets well clear: device makers cite fields as low as 5 to 10 gauss at the implant as enough to switch the device into a test mode, which a small neodymium magnet produces at several inches. And metal implants in an MRI are a question for the radiologist, who will ask exactly because some are fine and some are not.

Sleeping next to a magnet does nothing to you. Sleeping next to a large one and rolling onto it might.

No.

Because aircraft still carry a magnetic compass as a backup, and a package of strong magnets in the hold can swing it. Air-freight rules define "magnetized material" as anything producing more than 0.00525 gauss at 15 feet (about 4.6 m); a shipment above that limit has to be declared as dangerous goods, and above a higher threshold can't fly at all. Shippers meet the rule by packing magnets in alternating orientation and lining the box with steel so the stray field cancels and is contained, which is why a box of neodymium magnets arrives heavier than it looks. There is no equivalent limit for trucks and trains.

This one deserves more than a paragraph, so I gave it a whole page: How magnets are made — from mine to magnet walks through all thirteen steps, from ore to the final magnetizing pulse.

The very short version, for the impatient: a modern magnet is made as a powder, aligned in a magnetic field, pressed, sintered into a solid, machined, coated, and magnetized as the very last step. Until that final pulse, it's just a heavy gray block.

As for the first magnet: nature made it. Lodestone is magnetite that was magnetized — most likely by lightning — and was found pulling on iron in antiquity. Stroking an iron needle with lodestone gives you a compass, and from 1820 onward, electricity has done the job.

The rare earths are the fifteen lanthanide elements plus scandium and yttrium, a row of chemically similar metals near the bottom of the periodic table. Two of them make magnets: neodymium, in neodymium-iron-boron, and samarium, in samarium-cobalt. Two more — dysprosium and terbium — are added to neodymium magnets in small amounts to help them survive heat. Praseodymium rides along with neodymium in most magnets because the two are hard and pointless to separate fully. A "regular" magnet, by contrast, is ferrite (iron oxide with strontium or barium) or alnico, and contains no rare earth at all.

They aren't rare in the sense of not being anywhere in the world. Cerium, the most common, is more abundant in the Earth's crust than copper; neodymium is more abundant than lead, and there are deposits on every continent — see the global magnet supply-chain atlas for where. The name dates from the eighteenth century, when the oxides were hard to find and harder to tell apart. They are rare in the sense of being deposited in a concentration that makes them economical to mine. And even a good deposit is only the start: the elements occur together, behave almost identically in chemistry, and pulling out a single one at high purity takes hundreds of stages of solvent extraction. The rarity is in the concentration and the processing, not the rock — and today that processing is concentrated in a very small number of places.

Overwhelmingly in China, which produces around nine in every ten sintered neodymium magnets and a similar share of the refined rare-earth metal that goes into them. Japan is the other established producer, with a handful of firms that hold much of the original patent lineage. Germany has one significant maker. Everyone else — the United States, Europe, Korea, India, Vietnam — is somewhere between restarting and starting. The global magnet supply-chain atlas maps who does what, stage by stage, from mine to finished magnet.

The United States was one of the two places the neodymium magnet was invented and built the first plants in the 1980s, then lost nearly all of its production to Chinese pricing over the following two decades. Rebuilding began in earnest after 2020, driven by defense and electric-vehicle demand; new sintered neodymium magnet plants in Texas came online in the mid-2020s and several more are under construction or ramping. Domestic output is still a small fraction of what US motor makers consume, and it will be for some years; but for the first time in two decades the answer to "does the US make them" is yes.

Ferrite and alnico, which don't depend on rare earths, are made in many more places, including the United States.

Electricity and magnetism are two faces of one thing. A current in a wire makes a magnetic field around it; a magnetic field that changes near a wire pushes a current through it. Everything from a power plant to an earbud is one of those two sentences, arranged cleverly.

A generator is the second sentence: spin a magnet past coils of wire (or coils past a magnet) and current flows in the coils. Every turbine — steam, gas, wind, hydro — ends in one. A motor is the first sentence run in reverse: push current through a coil that sits in a magnet's field and the coil is shoved sideways; arrange the shoving to go around in a circle and you have rotation. A speaker is a motor that doesn't rotate. Its coil is glued to the paper cone and sits in the field of a ring magnet; the music signal is a current that wiggles the coil back and forth, and the cone wiggles the air. Complex sound is just a complex wiggle.

The permanent magnet's job in all of these is to supply the field for free. You could make it with a second coil and more current — early motors did — but a magnet gives you the same field with no power, no heat and no wire, which is why nearly every small motor and every speaker uses one.

With a magnet that moves. (I love eddy currents. If you've never seen an eddy-current separator flinging cans off a conveyor, watch this before reading on.) A steady magnet does nothing to aluminum, but a rapidly changing field induces electric currents in any conductor — eddy currents — and those currents make their own magnetic field, which pushes back against the one that created it. In an eddy-current separator, the waste stream rides a conveyor over a drum containing a magnet rotor spinning several thousand times a minute. Steel has already been lifted off upstream by an ordinary magnet. When an aluminum can reaches the drum, the whirling field induces currents in it and flings it forward off the belt, while glass, paper and plastic — non-conductors — simply drop. The same effect is what heats a pan on an induction cooktop, brakes a roller coaster without touching it, and lets a metal detector find a ring on the beach.

Slide, don't pull. Two magnets face-to-face are strongest in the direction that pulls them straight apart and much weaker sideways, so push one across the other until it's hanging off the edge, then lever it away. For anything larger than a coin, do it over the edge of a table with the lower magnet held down, and keep your fingers out of the path they'll take when they let go. Store strong magnets with a spacer between them or a steel keeper across the poles, and never toss a bag of them onto a workbench.

Don't cut or drill them. Sintered neodymium is as brittle as a ceramic and harder than most steels; a drill bit skates, chips the magnet, and the friction heats the material past its operating temperature and demagnetizes it locally. Worse, the fine powder that grinding throws off is metallic neodymium-iron and can heat up and ignite on its own. The factory machines magnets before they are magnetized, with diamond tooling under flood coolant, which is why buying the shape you need is always cheaper than making it.

The topic of bonding has been the focus of many, many years of my career in the industry and I could write multiple books about it. The single most important thing in gluing magnets is surface prep — get a clean, rough surface and it works. Scuff the nickel plating lightly, clean it, and use a two-part epoxy or a gel cyanoacrylate; for anything structural, buy magnets with a countersunk hole and screw them down. Glue holds a magnet to wood or plastic fine — it's the magnet-to-magnet or magnet-to-steel interface that fails, because the magnet will pull itself off a thin glue line toward the steel.