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Material World
Application

Permanent magnets

Materials that retain magnetisation without power — the component that makes electric motors and generators compact.

A permanent magnet holds its magnetic field without a current, which means a motor built around one needs no power to maintain its field and can be smaller and more efficient than one that does.

The modern rare-earth magnets are far stronger for their size than the ferrites and alnicos that preceded them, and that step change is what made compact hard drives, small high-torque motors and direct-drive wind turbines practical. It also made the supply of a handful of rare-earth elements a strategic question for industries that had never thought about them.

Uses

Traction motors in electric and hybrid vehicles, generators in direct-drive wind turbines, loudspeakers and headphones, hard disk drive actuators, magnetic separators, and the sensors and small motors distributed through modern vehicles and appliances in the dozens.

Performance at temperature is usually the binding constraint rather than raw strength, which is why magnet composition is adjusted with heavy rare earths for applications that run hot.

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.

uses

  • Neodymium — element · the base of the strongest commercial magnets
  • Praseodymium — element · substitutes for part of the neodymium with little loss of performance
  • Samarium — element · samarium-cobalt keeps its strength where neodymium magnets fail
  • Dysprosium — element · raises the temperature at which the magnet demagnetises
  • Neodymium magnet — alloy · the strongest in commercial use, and the reason a motor, a hard drive and an earbud can be small
  • Samarium–cobalt magnet — alloy · weaker and untroubled by heat, which keeps it where temperature rather than strength is the constraint
  • Ferrite — material · the hard grades, which are a tenth the strength of a neodymium magnet per unit volume and a small fraction of the price — loudspeakers, wiper motors, and every fridge magnet ever made

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Permanent magnets 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

  • Permanent magnets → uses (the strongest in commercial use, and the reason a motor, a hard drive and an earbud can be small) → 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
  • Permanent magnets → uses (weaker and untroubled by heat, which keeps it where temperature rather than strength is the constraint) → 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 (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
  • Permanent magnets → uses (the hard grades, which are a tenth the strength of a neodymium magnet per unit volume and a small fraction of the price — loudspeakers, wiper motors, and every fridge magnet ever made) → Ferrite → is produced by (the step before, where the milled oxides react together into the ferrite phase) → Calcination → takes as input (heated until the carbonate decomposes to lime and carbon dioxide) → Limestone → is sourced from (precipitated from it, mostly by organisms building shells and skeletons out of dissolved calcium and carbonate) → Seawater → is composed of (about 96.5 per cent by mass — seawater is 3.5 per cent dissolved solids and the rest of it is this) → Water
  • Permanent magnets → uses (the base of the strongest commercial magnets) → 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
  • Permanent magnets → uses (substitutes for part of the neodymium with little loss of performance) → 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
  • Permanent magnets → uses (samarium-cobalt keeps its strength where neodymium magnets fail) → 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

These are the most distinct paths back. Permanent magnets can be traced through others besides.