Dysprosium (Dy)

The Greek dysprositos means hard to get at, and Paul-Émile Lecoq de Boisbaudran chose it in 1886 out of exasperation. Separating his new oxide from holmium took him more than thirty successive precipitations, each one a marginal improvement on the last, with no way of knowing in advance how many would be needed.

The name aged into an accidental prophecy. Boisbaudran meant it was hard to purify; a century later dysprosium became hard to obtain, in a geopolitical sense, and that is now the most consequential thing about the element.

What happens to a magnet in a hot engine bay

Neodymium-iron-boron magnets are the strongest permanent magnets ever made, and they have one serious weakness. Their resistance to being demagnetised — coercivity — falls steeply as they warm, by roughly half a per cent for every degree. A magnet that is comfortably stable on the bench can lose its magnetisation irreversibly at the temperature inside a running motor.

Traction motors in electric vehicles run at 150 °C and above. Generators in direct-drive wind turbines sit inside sealed nacelles. Both are exactly the conditions a plain neodymium magnet handles worst.

Dysprosium is the fix. Substituting dysprosium atoms for some of the neodymium in the magnetic phase raises its magnetocrystalline anisotropy — loosely, how strongly each crystal insists on holding its magnetisation along one particular axis — and a higher anisotropy field means higher coercivity and a higher safe operating temperature.

The trade-off is real and worth stating plainly, because dysprosium is often described as simply making magnets better. It does not. Dysprosium's magnetic moment couples to the iron in the opposite sense to neodymium's, so every dysprosium atom added subtracts from the magnet's total field strength. What you buy with dysprosium is thermal stability, and you pay for it in remanence. Magnet designers use as little as they can get away with, and reducing that quantity has been a sustained industrial effort — from several per cent of magnet mass in early automotive grades down toward one per cent or less, largely by diffusing heavy rare earths in from the surface rather than alloying them throughout.

Where the heavy rare earths actually come from

"Rare earth supply" is usually discussed as one problem. It is two, and they are not similar.

The light rare earths — lanthanum, cerium, neodymium, praseodymium — are genuinely abundant. Bastnäsite deposits like Mountain Pass in California carry them at grades measured in whole per cent rather than in parts per million, mining them is a normal mining business, and production is diversifying across several countries.

Dysprosium is not in those deposits in any useful concentration. The heavy rare earths concentrate instead in ion-adsorption clays: deeply weathered granites in which the heavy rare earth ions cling loosely to clay minerals and can be washed out with a salt solution. Economic deposits of this type are known in a small number of places, and the overwhelming majority of world production has come from southern China — Jiangxi and its neighbours — together with Kachin State in northern Myanmar, whose ore feeds Chinese separation plants.

That concentration is why dysprosium appears at the top of every critical-minerals list. In April 2025 China placed export licensing controls on a group of medium and heavy rare earths including dysprosium and terbium, and the effect on magnet manufacturers outside China was immediate — there is no substitute element, and no alternative producer at scale that can be brought on in less than several years.

The clays carry an environmental cost that rarely appears in the discussion. In-situ leaching with ammonium sulfate strips the hillside's rare earths and leaves behind acidified soil and contaminated groundwater, and the informal operations that supplied much of the early Chinese production did enormous local damage.

Also very good at absorbing neutrons

Dysprosium's second family of uses has nothing to do with magnetism and everything to do with its nucleus. Natural dysprosium has a thermal neutron cross-section near 940 barns, high enough to make it a practical reactor control material.

Dysprosium titanate control rods have replaced boron carbide in Russian VVER reactors, and the reason is mechanical rather than nuclear. Boron carbide absorbing a neutron produces helium, which builds up as gas pressure and swells the rod, so boron carbide rods have a limited life. Dysprosium titanate produces no gas, does not swell, and tolerates high temperature, so the rod lasts several times longer.

The same nuclear property, in a very different setting, makes dysprosium a dosimetry material. Calcium sulfate doped with dysprosium is one of the standard thermoluminescent phosphors used in the radiation badges worn by radiographers, nuclear workers and researchers: radiation absorbed by the crystal is stored in trapped electron states, and heating the badge releases that energy as light in proportion to the dose received.

Second only to holmium

Among the elements, dysprosium has one of the largest magnetic moments per atom — surpassed only by holmium, its immediate neighbour. That raw magnetic strength is what makes dysprosium useful in pole pieces for research magnets producing the highest attainable fields, and it is why dysprosium is a component of the giant-magnetostrictive alloy developed for sonar.

Dysprosium iodide also appears in metal halide lamps, where its many emission lines fill in the gaps between the sparse lines of mercury and sodium and produce the continuous, high colour-rendering white light used in film and television lighting.

Seven isotopes, and a metal that arrived late

Dysprosium has seven naturally occurring isotopes, an unusually even spread for a lanthanide, with dysprosium-164 the most abundant at around 28%. Dysprosium-164 is also the individual isotope responsible for most of the element's neutron appetite.

The element itself was a laboratory abstraction for most of its first seventy years. Boisbaudran had an impure oxide; nobody had the metal. Reasonably pure dysprosium metal only became available in the 1950s, when Frank Spedding's group at the Ames Laboratory adapted ion-exchange chromatography — the same technique that had settled the identity of promethium — to separating the rare earths in quantity. Every industrial use of dysprosium postdates that, which is why an element discovered in 1886 has an industrial history that only really begins in the 1980s.