1 · MagnetsStart with the word
A magnet is anything that produces a magnetic field of its own. That covers a fridge magnet, a block of iron sitting inside a coil, and a coil with nothing inside it at all.
The word comes from Magnesia, the region of ancient Anatolia where lodestone — naturally magnetized iron ore — was first noticed pulling on iron.
1 · MagnetsWhat a field does
A magnetic field pulls on iron, pushes or pulls on other magnets, and — the reason it matters commercially — exerts force on moving electric charge. That last property is what turns a magnet into a motor, a generator, a loudspeaker, or a sensor.
1 · MagnetsOne word, three things
Split the family by where the field comes from and whether it stays.
Soft magnetic materials carry a field only while one is applied, then let it go. Hard magnetic materials — permanent magnets — keep their field. Electromagnets make a field from electric current, and lose it the moment the current stops.
1 · MagnetsThe overlaps are the products
Almost nothing useful sits in one circle alone. A coil wound on an iron core is soft plus electro. A clamp that switches a permanent magnet on and off with a pulse of current is hard plus electro. A few alloys sit between soft and hard and are used for exactly that reason.
And in the middle, using all three at once, is the permanent‑magnet motor. We come back to it at the end.
2 · Soft magnetsMaterials that amplify
Put a soft material in a magnetic field and it multiplies the flux passing through it — often by thousands. Take the field away and it lets go.
The loop on the right is the signature. Its height is how much flux the material can carry before it saturates. Its width is how hard it resists changing — the coercivity. A good soft material is tall and very thin: nearly a line.
The job: steer and concentrate flux — transformer cores, motor laminations, magnetic shields.
2 · Soft magnetsIron
Pure, annealed iron carries more flux than almost anything else, and it is cheap. Its weakness is electrical: iron conducts, so a changing field stirs up wasted currents inside it that show up as heat.
Used where the field holds still: relay cores, pole pieces, DC electromagnets.
2 · Soft magnetsSilicon iron
Add a few percent silicon and iron's electrical resistance rises, cutting the wasted currents, at a small cost in flux. Rolled into thin sheet and stacked as laminations, it is the core of nearly every transformer and motor on earth. By tonnage, the most important magnetic material there is.
Grain‑oriented sheet is rolled so the crystals line up along one direction, for transformers; non‑oriented sheet is for motors, where the field rotates.
Used in: transformers, induction and permanent‑magnet motor stators, generators.
2 · Soft magnetsCobalt iron
Alloy iron with roughly half cobalt — sold as Permendur or Hiperco — and saturation reaches the highest of any practical material. The same flux from less metal, which is the whole argument when a kilogram of aircraft costs more than a kilogram of cobalt.
It is expensive, brittle, and slightly harder to magnetize than iron; the loop is a touch wider.
Used in: aircraft generators, high‑performance motors, actuators where mass is the constraint.
2 · Soft magnetsMu‑metal
A nickel‑iron alloy, about four‑fifths nickel, that trades away most of iron's saturation for extreme ease of magnetization. The loop is short and almost vertical: the faintest field moves it.
That makes it a shield. Wrap an instrument in mu‑metal and stray flux takes the easy path through the alloy rather than crossing the space inside. It is delicate — machining or denting it undoes the annealing that gives it those properties.
Used in: shielding for sensors, electron optics and lab instruments; small‑signal transformer cores.
3 · Hard magnetsMaterials that remember
A hard material's loop is wide. Magnetize it once and it holds; it takes a large reverse field to undo it. The width of the loop is the entire point — it is what "permanent" means. Here is the full loop of an alnico magnet. Note the field axis: it is now in thousands of amperes per meter, and alnico is the least coercive material in this section.
3 · Hard magnetsKeep the second quadrant
In service a permanent magnet always faces a field pointing against it — its own, plus whatever the circuit applies — while still delivering flux forward. Only the upper‑left quadrant of the loop describes that, so it is the only part datasheets publish: the demagnetization curve.
Read it two ways. Higher on the vertical axis means more flux. Farther to the left means harder to demagnetize. Every hard magnet that follows is drawn on this one plot, in order of discovery.
3 · Hard magnets · 1930sAlnico
Aluminum, nickel, cobalt and iron. Alnico delivers a lot of flux and is superbly stable with temperature — it works red‑hot. But its coercivity is low: the curve drops almost straight down, and the magnet can be partly demagnetized by its own shape or by a nearby field. It has to be made long and thin, which is why old magnets are horseshoes.
Still used in: sensors, instruments, guitar pickups, and anywhere the temperature rules out rare earths.
3 · Hard magnets · 1950sFerrite
Iron oxide fused with strontium or barium — a ceramic made, in effect, from rust. Weak: a third of alnico's flux, a quarter of a neodymium magnet's. But cheap, corrosion‑proof, electrically insulating, far harder to demagnetize than alnico, and it gets harder still as it warms — the opposite of every other material here.
By tonnage the most produced magnet in the world: small motors, loudspeakers, separators, the fridge door.
3 · Hard magnets · 1960sSamarium cobalt, 1:5
The first rare‑earth magnet: one samarium atom to five cobalt. The rare earth's contribution is coercivity, and it is enormous — the B curve runs in a straight line all the way to the axis, and the J curve runs clean off the edge of the chart; most test equipment cannot reach the field needed to reverse it. Nothing in a normal circuit knocks it down.
Less flux than alnico, but it can be made into any shape and it stays magnetized. This combination is what made small, powerful motors possible.
3 · Hard magnets · 1970sSamarium cobalt, 2:17
The second generation adds iron, copper and zirconium to the cobalt: about a fifth more flux than 1:5, usable at higher temperatures than any rare‑earth magnet since. Its J curve has a different shape — flat to a knee far out near the edge of the chart, then a gradual slope rather than a cliff — which is the signature of how this alloy resists demagnetization. It is expensive — samarium and cobalt both — and brittle.
Used where neodymium can't go: hot environments, aerospace and defense, downhole tools, high‑reliability instruments.
3 · Hard magnets · 1983Neodymium iron boron
Discovered independently at Sumitomo and General Motors in the same year. The most flux per gram of any commercial magnet, from elements far cheaper than samarium and cobalt, and a very square J curve: it holds everything until the reverse field reaches its limit, then lets go almost at once. It is the material behind nearly every high‑performance motor built today.
Its weakness is heat. As the magnet warms, coercivity falls fast and the J curve develops a knee — the faint curve on the right is the same magnet, hot. Operate past that knee and the loss is permanent. That knee is where most diligence questions about a magnet start.
3 · Hard magnets · A subcategoryGrain‑boundary‑diffused NdFeB
The fix for heat used to be blending heavy rare earths — dysprosium, terbium — through the whole alloy. That raises coercivity, but it costs flux, and those two elements are the scarcest and most expensive in the supply chain.
Grain boundary diffusion instead soaks the heavy rare earth in from the surface of a finished magnet, along the boundaries between grains, so it sits only where it is needed. The result keeps the flux of the base grade, pushes the square drop well to the left — into samarium‑cobalt territory — and uses a fraction of the dysprosium. This is the magnet in an EV traction motor.
4 · FrontierIron nitride
The dotted curves that follow are estimates, not datasheets. Theory says one particular iron‑nitrogen compound, Fe₁₆N₂, could carry more flux than any magnet ever made — with no rare earth and no cobalt. The catch is coercivity and stability: the phase falls apart when heated, and bulk magnets made so far sit well below the theoretical line.
Status: in commercialization for lower‑performance motors. Treat the dotted line as a ceiling.
4 · FrontierTetrataenite
An ordered iron‑nickel crystal found in meteorites, where it formed over millions of years of slow cooling. Its intrinsic properties would put it in the neighborhood of samarium cobalt, from two of the cheapest metals there are.
Laboratory routes to form it in hours rather than millennia have been reported. A bulk magnet showing the predicted coercivity has not. The dotted curve is what the crystal permits, not what anyone has held.
5 · ElectromagnetsFields from current
Pass current through a coil of wire and a field appears; stop it and the field is gone. More current, or more turns, means more field. That is the whole principle — the plot on the right is now field against current, not field against field.
Electromagnets divide by what drives them and what limits them.
5 · ElectromagnetsDC electromagnets
A coil in air makes a feeble field before the copper overheats. Put a soft iron core inside it and the field is multiplied — up to the point where the iron saturates, near two tesla, and then no further. Every practical DC electromagnet lives on that curve.
Used in: relays and contactors, solenoid valves, scrapyard lifting magnets, laboratory magnets.
5 · ElectromagnetsAC electromagnets
Alternating current drives the core around its loop fifty or sixty times a second — thousands, in a power supply. Every lap costs the loop's area in heat, plus the wasted currents from earlier. That is why AC cores are laminated silicon iron, and why the soft branch of this map is an industry of its own.
Used in: transformers, induction motors, induction heaters, wireless chargers.
5 · ElectromagnetsSuperconducting magnets
Leave the iron out and the field is limited only by current — and copper's limit is heat. A superconductor carries current with no resistance at all, so the coil can be driven far past where iron saturates: ten, twenty tesla and beyond.
The price is cold. The coil must be held near absolute zero, and the energy stored in it has to be managed if it ever warms and stops superconducting.
Used in: MRI scanners, particle accelerators, fusion machines, research magnets.
6 · TogetherThe motor in the middle
A permanent‑magnet motor is all three circles at once. Hard magnets on the rotor supply the field. Soft laminations in the stator steer it. Copper windings — electromagnets — push against it, and the rotor turns.
Each circle is a different industry, with different raw materials, different makers, and different risks. When someone says "the magnet market," the first question is which circle they mean.