Neodymium (Nd)

Two teams on opposite sides of the Pacific arrived at the same compound in 1982 without knowing about each other, and both turned up at the same conference in Pittsburgh in November 1983 to announce it. Masato Sagawa at Sumitomo Special Metals had reached Nd₂Fe₁₄B by powder metallurgy and sintering; John Croat at General Motors Research had reached it by melt-spinning ribbon at enormous cooling rates. Neither had any idea the other existed until the programme was printed.

They were both there because of cobalt. The strongest magnets available in the 1970s were samarium-cobalt, and the fighting in Zaire's Shaba province in 1977 and 1978 sent the cobalt price up by a factor of several within months. Two large industrial research organisations independently concluded that a permanent magnet dependent on cobalt was a strategic liability and went looking for one based on iron. The most consequential magnetic material of the last half-century exists because of a supply shock in central Africa.

The patent conflict was settled by dividing the technology rather than the market: Sumitomo took sintered magnets with grain sizes above a micrometre, General Motors took the finer-grained melt-spun material used in bonded magnets.

What each element in the formula is for

Neodymium iron boron works because the three components do three different jobs, and no single element does all of them.

Iron supplies the magnetisation — the raw strength of the field — because iron atoms carry large magnetic moments and pack densely. What iron alone cannot do is hold that magnetisation in a particular direction; a lump of soft iron demagnetises the moment you remove the field. The neodymium supplies anisotropy: its 4f electrons have a strongly non-spherical charge distribution that couples to the crystal's electric field, so the magnetisation strongly prefers one axis of the tetragonal lattice and resists being turned away from it. Boron is not magnetic at all; it stabilises the crystal structure that puts the other two in the right arrangement.

The result reaches an energy product around ten times that of a ferrite magnet of the same size. That number is what changed the engineering, because it means the same magnetic work can be done by a tenth of the volume.

Everything got smaller

The consequences appeared first in things people hold. Headphone drivers shrank from the pads of the 1980s to earbuds, because a small neodymium magnet moves a diaphragm as forcefully as a large ferrite one. Hard disk drives got their voice-coil actuators, which is why heads could be moved across a platter quickly enough for random access to keep improving. Cordless power tools became usable. Loudspeakers in laptops and phones exist at all.

The larger consequences came later and are still unfolding. A direct-drive wind turbine generator avoids a gearbox — the component that fails most often offshore — by using a very large permanent magnet rotor, and needs several hundred kilograms of magnet per megawatt. And the traction motor of most electric and hybrid vehicles is a permanent-magnet synchronous machine containing on the order of a kilogram or two of neodymium and praseodymium, chosen because it is the most efficient and compact option available.

The heat problem, and what it drags in

Neodymium iron boron has one serious weakness: its Curie temperature is only a little over 300 °C, low for a magnet, and its resistance to being demagnetised falls steeply well before that. A motor running at 150 to 200 °C inside a car will simply lose field strength.

The fix is to substitute a small amount of dysprosium or terbium for neodymium, particularly at the grain boundaries where demagnetisation begins, which raises coercivity substantially at the cost of a little magnetisation. These are heavy rare earths, far scarcer and more expensive than neodymium, and the industry has spent two decades learning to use less of them — grain boundary diffusion processes now deposit them only where they are needed rather than through the bulk.

The magnets also corrode, unlike ferrite, so essentially all of them are nickel-plated or epoxy-coated. An unprotected neodymium magnet in damp air degrades visibly.

Ninety per cent of the separation capacity

Neodymium is not geologically scarce. What is scarce is the industrial capacity to separate it from the fourteen chemically similar elements it comes out of the ground with, and to turn the oxide into alloy and then into magnets. That capacity is overwhelmingly in one country.

The path there is worth stating plainly. Mountain Pass in California supplied most of the world's rare earths into the 1990s and closed after regulatory problems with wastewater discharges. General Motors sold its magnet business, Magnequench, in 1995 to a consortium with Chinese state-linked partners, and the production moved to China. By the 2000s, Chinese separation plants handled the large majority of world output regardless of where the ore was mined.

The leverage that creates has been used more than once. In 2010, export quotas were cut sharply and shipments to Japan were disrupted during a diplomatic dispute; prices rose several-fold, a wave of Western mining projects was announced, the WTO ruled the quotas non-compliant in 2014, quotas were removed, prices collapsed and most of those projects died. In April 2025 export licensing was imposed on seven medium and heavy rare earths — including the dysprosium and terbium that motor magnets need — and on magnets containing them. Neodymium itself was not on the list and it made no difference: finished magnets were caught, shipments fell sharply, and carmakers in the United States and Europe cut production and idled plants within weeks.

Motor designers have responded by building machines that need less magnet or none at all — wound-rotor and induction designs, and ferrite-assisted synchronous reluctance motors. Several are in production vehicles. They are somewhat less efficient, and they are chosen partly as insurance.

A hundred and ninety-two beams of neodymium glass

Neodymium's other great application is optical. Nd³⁺ has an energy-level structure almost tailor-made for a four-level laser, and doped into a host it gives the transition that more solid-state lasers are built around than any other.

Its most spectacular incarnation is the National Ignition Facility in California, whose 192 beams are amplified by slabs of neodymium-doped phosphate glass. Glass rather than crystal, because nobody can grow a crystal that large and uniform. In December 2022, that machine delivered more energy out of a fusion target than the laser put into it — the first controlled fusion ignition, achieved with light that had been amplified by a lanthanide.

Neodymium colours glass too, and unusually. Nd³⁺ absorbs in a narrow band in the yellow, so neodymium glass looks lavender under daylight and shifts towards blue under an incandescent lamp, which is rich in the yellow the glass removes. Light bulbs coated with neodymium glass are sold as "daylight" bulbs on exactly that principle: they do not add blue, they subtract yellow.

Samarium in, neodymium out

Samarium-147 decays by alpha emission to neodymium-143 with a half-life of about 106 billion years, and the pair makes one of geology's most reliable clocks.

Its advantage is chemical stubbornness. Both parent and daughter are rare earths, both are held tightly in the same minerals, and neither moves readily in the hot fluids that circulate during metamorphism — which is exactly the weakness of rubidium-strontium dating, where both elements travel easily and ages are frequently reset. Samarium-neodymium therefore reads through events that erase other systems, and it has dated the oldest surviving crustal rocks and the lunar samples returned by Apollo.

The same isotopes serve as a tracer rather than a clock. Because the ratio of neodymium-143 to neodymium-144 in a reservoir depends on how much samarium it has carried and for how long, the mantle and the continental crust have measurably different values. Geochemists express this as epsilon-Nd and use it to determine whether a given volcanic rock came from depleted mantle or recycled crust, and to trace where deep ocean water masses have been.

Neodymium's name is the least apt in the periodic table. Carl Auer von Welsbach called it the "new twin" in 1885 when he split Mosander's didymium in two, and the merely descriptive half of a name coined for a mixture now belongs to the element that reorganised the electric motor industry.