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Material World
Alloy

Neodymium magnet

Neodymium, iron and boron in a structure that holds a magnetic field better than anything else known — and the reason a hard drive, an earbud and an electric motor can be small.

Collectible specimen

The neodymium magnet is the strongest permanent magnet in commercial use, by a wide margin, and its arrival in the 1980s is one of the clearer cases of a single material changing what engineers could build. A motor built around one is smaller and more efficient than the same motor built around a ferrite; a hard drive's read head can move faster; a loudspeaker can be a fraction of the size.

The magnetism comes from the compound Nd₂Fe₁₄B, and specifically from the way its crystal structure holds the neodymium atoms' magnetic moments locked along one axis. That locking — magnetocrystalline anisotropy — is what a permanent magnet needs and what most materials lack.

Processing

The alloy is melted, cast, milled to a powder of single-crystal particles a few microns across, and then pressed in a magnetic field so that every particle's easy axis points the same way. Sintering fuses the powder into a solid, and the block is magnetised at the end.

Heat is the standing weakness. The plain composition begins losing its field not far above 100 °C, which is a problem for a traction motor, and the fix is to substitute dysprosium or terbium for a few per cent of the neodymium. Both are heavy rare earths, both are far scarcer than neodymium, and reducing the amount needed is one of the more active materials-research goals there is.

The alloy also corrodes readily, so essentially every commercial magnet is plated — usually nickel over copper over nickel — and a chipped coating will eventually turn the magnet to powder.

Economic significance

Neodymium magnets are where a large share of the world's rare earth production ends up, and they are the reason rare earths are discussed as a strategic question at all. An electric vehicle traction motor contains on the order of a kilogram of magnet; a direct-drive wind turbine contains hundreds of kilograms.

That concentrates a supply risk in an unusually specific place. Neodymium is not especially rare in the crust — it is more abundant than lead — but separated neodymium, and still more so dysprosium, comes from a small number of operations, and the magnet is the point at which almost every electrified technology touches them.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is composed of

  • Neodymium — element · 27–32% · the element the magnet is named for, and around a third of it by mass
  • Iron — element · 62–68% · the bulk of the alloy, and the reason it is cheap enough to put in a toy
  • Boron — element · 1–1.5% · about one per cent, and structurally essential — the compound is Nd₂Fe₁₄B, and without the boron it does not form
  • Praseodymium — element · 0–8% · substituted for part of the neodymium, and usually left in rather than separated out — the two behave nearly identically here and separating them costs money for no benefit
  • Dysprosium — element · 0–8% · a few per cent in the grades that have to work hot, which is what a traction motor needs — and the single most supply-constrained ingredient in the magnet
  • Terbium — element · 0–3% · the same job as dysprosium at lower addition rates and higher cost

is used as

  • Permanent magnets — application · the strongest in commercial use, and the reason a motor, a hard drive and an earbud can be small

is an alternative to

  • Samarium–cobalt magnet — alloy · neodymium wins on every measure a datasheet lists, and none of those is the one an engine bay or a satellite cares about
  • Ferrite — material · where the magnet merely has to work rather than be small. Designers moved products back to ferrite within a year of the 2011 neodymium price spike, and some stayed — which is a useful corrective to the idea that a better material wins permanently

is produced by

  • Alloying and melting — process · melted, cast, milled to single-crystal powder, pressed in a magnetic field and sintered — the alignment step is what makes it a magnet rather than an alloy

is used in

  • Energy generation — industry · direct-drive wind turbine generators, which is what put rare-earth supply into energy policy

Sources

  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Neodymium magnet back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Neodymium magnet → is composed of (the bulk of the alloy, and the reason it is cheap enough to put in a toy) → Iron → is produced by (as pig iron, high in carbon and brittle until refined) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation → takes as input (the feedstock, and an unusual one in being free, unlimited and available anywhere — the cost is entirely the energy to liquefy it) → Air
  • Neodymium magnet → is composed of (about one per cent, and structurally essential — the compound is Nd₂Fe₁₄B, and without the boron it does not form) → Boron → is produced by (magnesium reducing boron oxide, which gives an impure amorphous boron — the crystalline element needs a different route entirely) → Metallothermic reduction → takes as input (the cheapest reducing metal and the commonest, and the aluminium in thermite) → Aluminium → is extracted from (via alumina — bauxite is refined by the Bayer process before smelting) → Bauxite → is sourced from (the residue of prolonged tropical weathering, which strips the silica and alkalis out of an aluminosilicate rock and leaves the aluminium behind — basalt is one common parent among several) → Basalt
  • Neodymium magnet → is produced by (melted, cast, milled to single-crystal powder, pressed in a magnetic field and sintered — the alignment step is what makes it a magnet rather than an alloy) → Alloying and melting → takes as input (the base metal of both brass and bronze) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Neodymium magnet → is composed of (the element the magnet is named for, and around a third of it by mass) → Neodymium → is produced by (a light rare earth, separated from its neighbours by countercurrent solvent extraction) → Rare earth separation → takes as input (the principal ore of the light rare earths, carrying all of them together) → Bastnäsite
  • Neodymium magnet → is composed of (the same job as dysprosium at lower addition rates and higher cost) → Terbium → is produced by (a heavy rare earth; the separation is the same cascade, run longer because the differences are smaller) → Rare earth separation → takes as input (the principal ore of the light rare earths, carrying all of them together) → Bastnäsite
  • Neodymium magnet → is composed of (substituted for part of the neodymium, and usually left in rather than separated out — the two behave nearly identically here and separating them costs money for no benefit) → Praseodymium → is produced by (a light rare earth, separated from its neighbours by countercurrent solvent extraction) → Rare earth separation → takes as input (the principal ore of the light rare earths, carrying all of them together) → Bastnäsite

These are the most distinct paths back. Neodymium magnet can be traced through others besides.

Downstream — what it becomes