WhereIsAtlas · Materials science

Rare earth magnets

The strongest permanent magnets ever made — discovered by accident in a US Air Force lab, then invented twice in 1983 by GM and a Japanese rival

Active — Rare earth magnets are the strongest permanent magnets known, and they are in active, growing use — in electric vehicle motors, wind turbines, headphones, hard drives and defence systems. The technology was born in a US Air Force laboratory in 1966 and reinvented twice over in 1983 by competing teams at General Motors and Sumitomo Special Metals.

Rare earth magnets are the strongest permanent magnets ever made, and they exist because of a discovery about the rare earth elements themselves. Those elements were slow to be understood: the first rare earth mineral was described in 1751, and the chemistry only began in earnest in 1787 when a dense black mineral was found near Ytterby in Sweden and analysed into a new "earth". Most individual rare earth elements were not separated until the late 19th and early 20th centuries, and samarium — which would later matter enormously — was identified spectroscopically in 1879.

The first rare earth permanent magnets were samarium-cobalt, developed in the 1960s and early 1970s. The founding breakthrough is credited to Karl J. Strnat and colleagues at the U.S. Air Force Materials Laboratory, who in 1966 identified exceptionally high magnetocrystalline anisotropy in rare earth-cobalt alloys. The resulting SmCo₅ magnet tripled the energy product of the Alnico magnets it replaced, and a second generation, Sm₂Co₁₇, followed in the 1970s with greater strength still.

Then came the leap that made rare earth magnets a foundation of modern industry. Neodymium-iron-boron — NdFeB — was invented independently in 1983 by two teams working either side of the Pacific: one led by John J. Croat at General Motors in the United States, and one led by Masato Sagawa at Sumitomo Special Metals in Japan. Both announced their results at the same conference in Pittsburgh that year. It is one of the clearest examples in industrial history of simultaneous invention.

The two routes then diverged commercially. General Motors commercialised its version through its Magnequench division, which it spun out in 1995, focusing on bonded and hot-pressed magnets. Sumitomo Special Metals developed the sintered process and secured the dominant patent position, and its business later became part of Hitachi Metals — still a major producer of sintered NdFeB.

The strategic consequence is that rare earth magnets are now overwhelmingly made in China, using raw material that in the West has largely come from a single Californian mine. That combination — a technology the modern world depends on, concentrated in one country at every stage — is why magnets went from a materials-science achievement to a matter of national policy.

Quick facts

What they are
the strongest permanent magnets known
First generation
samarium-cobalt (SmCo₅), from 1966
Founding breakthrough
Karl J. Strnat, U.S. Air Force Materials Laboratory, 1966
Second generation
Sm₂Co₁₇, 1970s
Strongest type
neodymium-iron-boron (NdFeB)
NdFeB invented
1983, independently by GM (John J. Croat) and Sumitomo (Masato Sagawa)
Announced
at the same Pittsburgh conference, 1983
Commercial routes
GM's Magnequench (bonded, hot-pressed) vs Sumitomo/Hitachi Metals (sintered)
Used in
EV motors, wind turbines, headphones, hard drives, defence systems

Lineage — where the name went

Rare earth magnets are a technology, not a company — so this tree follows the technology itself, branching into the two great generations and the rival corporate routes that commercialised the second one.

  1. 1966 — Rare earth magnets created Samarium-cobalt (SmCo₅) (first generation, from Strnat's USAF work)
  2. 1966 — Karl J. Strnat created Samarium-cobalt (SmCo₅) (identified the effect in rare earth-cobalt alloys)
  3. 1970s — Samarium-cobalt (SmCo₅) created Sm₂Co₁₇ (a stronger second generation)
  4. 1983 — Rare earth magnets created Neodymium-iron-boron (NdFeB) (the leap that made rare earth magnets ubiquitous)
  5. 1983 — John J. Croat created Neodymium-iron-boron (NdFeB) (at General Motors)
  6. 1983 — Masato Sagawa created Neodymium-iron-boron (NdFeB) (at Sumitomo Special Metals)
  7. 1995 — General Motors spun off Magnequench (GM's magnet business, to commercialise its route)
  8. Sumitomo Special Metals merged into Hitachi Metals (Sumitomo Special Metals became part of Hitachi Metals)

Entities in this tree: Rare earth magnets (product); Karl J. Strnat (person, 1966); Samarium-cobalt (SmCo₅) (product, 1966); Sm₂Co₁₇ (product, 1970s); John J. Croat (person, 1983); Masato Sagawa (person, 1983); Neodymium-iron-boron (NdFeB) (product, 1983); General Motors (company); Magnequench (company, 1995); Sumitomo Special Metals (company); Hitachi Metals (company)

Sources

  1. The men who made the magnet that made the modern world — IEEE Spectrum (2026-09-15)
  2. John J. Croat — biography and NdFeB work at General Motors — Engineering and Technology History Wiki (ETHW) (2026-09-15)
  3. A technical guide to the discovery and enduring legacy of samarium-cobalt rare-earth magnets — BenchChem (2026-09-15)
  4. SmCo magnets — technical data sheet — Quadrant (2026-09-15)
  5. Rare earth mining may be key to our renewable energy future — but at what cost? — Ames National Laboratory (Science News) (2026-09-15)
  6. Mountain Pass history and timeline — MP Materials (2026-09-15)

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