How neodymium magnets are made

The strongest permanent magnets sold are sintered from powder, aligned by an electromagnet while they are pressed.

stations: 8
things upstream: 9
raw sources: 6
steps from the ground: 3

The short version

A neodymium magnet is made from an alloy of neodymium, iron and boron. The alloy is melted, cast into ingots, milled to a fine powder, pressed in a strong magnetic field so the grains line up, and sintered into dense blocks. The blocks are heat-treated, cut, plated against corrosion, and magnetized last.

Melt the alloy

Neodymium, extracted from rare earth ore, is melted in a furnace with iron and boron. The target compound is Nd2Fe14B, which has a tetragonal crystal structure.

Goes in
Rare earth ore
Cast ingots

Molds take the melt, and it cools to form ingots of the alloy.
Mill to powder

Ingots are pulverized and milled to a fine powder, each grain a tiny crystal.
Align and press the powder

Grains of the microcrystalline powder are lined up in a powerful magnetic field during manufacture. Each crystal magnetizes easily along one axis, and holding them parallel is what gives the finished block its strength.
Sinter into dense blocks

The pressed powder is heated until the grains fuse into a dense solid block without melting the whole mass.
Heat-treat and cut

The blocks are heat-treated, then cut to the shape the customer needs.
Plate the surface

Sintered magnets corrode along their grain boundaries and can crumble into powder. A coating of nickel, nickel-copper-nickel or zinc is the standard defense.

Goes in
Nickel Zinc
Magnetize it last

Only at the end is the finished block magnetized. Bonded magnets, a second kind, instead use melt-spun ribbon crushed and mixed with polymer, then molded.

End of the lineNeodymium magnet Next it goes into headphones, wind turbine, wireless earbuds and 3 more.

Worth repeating

General Motors and Sumitomo Special Metals discovered the neodymium-iron-boron compound independently, almost at the same time, in 1984.
By energy per volume, a neodymium magnet is about 18 times stronger than an ordinary ferrite magnet.
Above 100 °C the coercivity of a neodymium magnet drops sharply, and its Curie temperature is around 320 °C.