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Material World
Alloy

Samarium–cobalt magnet

Weaker than a neodymium magnet and untroubled by heat — the permanent magnet used where temperature rather than strength is the constraint.

Samarium–cobalt was the first rare earth magnet, developed in the 1960s, and neodymium-iron-boron displaced it from most applications within twenty years by being stronger and much cheaper. It did not disappear, because it holds two advantages that no amount of strength substitutes for.

It works hot. Its Curie temperature is around 800 °C against roughly 310 °C for a neodymium magnet, and its field falls away far more slowly as it warms — so it keeps the aerospace actuators, the traction motors that run at temperature, and the instruments that must not drift. And it does not corrode, so unlike neodymium it needs no plating.

Economic significance

The cobalt is both the reason it works and the reason it is expensive, and it puts the magnet in the same supply conversation as batteries — a market vastly larger than magnets, and one that sets the price.

Its continued use is a good illustration of why a superseded material does not simply vanish. Neodymium magnets beat samarium–cobalt on almost every measure a datasheet lists, and none of those measures is the one an engine bay or a satellite actually cares about.

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

  • Samarium — element · 20–35% · the rare earth that supplies the anisotropy, and essentially the only large use samarium has
  • Cobalt — element · 60–80% · the balance, and both the reason it works hot and the reason it is expensive

is used as

  • Permanent magnets — application · weaker and untroubled by heat, which keeps it where temperature rather than strength is the constraint

is an alternative to

  • Neodymium 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

is produced by

  • Alloying and melting — process · by the same sintering route, and needing no plating afterwards because unlike neodymium it does not corrode

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 Samarium–cobalt 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

  • Samarium–cobalt magnet → is composed of (the balance, and both the reason it works hot and the reason it is expensive) → Cobalt → is sourced from (much of world supply arrives as a by-product of copper mining rather than from cobalt-first operations) → 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
  • Samarium–cobalt magnet → is produced by (by the same sintering route, and needing no plating afterwards because unlike neodymium it does not corrode) → 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
  • Samarium–cobalt magnet → is composed of (the rare earth that supplies the anisotropy, and essentially the only large use samarium has) → Samarium → 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
  • Samarium–cobalt magnet → is composed of (the balance, and both the reason it works hot and the reason it is expensive) → Cobalt → is sourced from (much of world supply arrives as a by-product of copper mining rather than from cobalt-first operations) → Copper → is extracted from (the principal copper ore worldwide) → Chalcopyrite
  • Samarium–cobalt magnet → is composed of (the rare earth that supplies the anisotropy, and essentially the only large use samarium has) → Samarium → is produced by (a light rare earth, separated from its neighbours by countercurrent solvent extraction) → Rare earth separation → takes as input (the other feed alongside bastnäsite, bringing thorium into the residues with it) → Monazite
  • Samarium–cobalt magnet → is composed of (the rare earth that supplies the anisotropy, and essentially the only large use samarium has) → Samarium → is produced by (a light rare earth, separated from its neighbours by countercurrent solvent extraction) → Rare earth separation → takes as input (the heavy rare earth feed, where monazite and bastnäsite bring the light ones) → Xenotime

These are the most distinct paths back. Samarium–cobalt magnet can be traced through others besides.

Downstream — what it becomes