Heavy rare earths — dysprosium and terbium — are the secret ingredient that lets NdFeB magnets survive hot environments like EV drive motors. There is just one problem: they are expensive. Sputtering is a clever way to use far less of them, by putting the element only where it actually works.
The old way: mix it all in
Traditionally, dysprosium is melted straight into the alloy, so it ends up everywhere in the magnet — inside the grains, where it does almost nothing, and at the grain boundaries, where it does all the work. High-temperature grades can carry more than 10% dysprosium by weight, and you pay for every gram.
The sputtering way: season only the surface
Sputtering works like an ultra-fine spray paint. In a vacuum chamber, a gas is turned into a plasma and its ions knock atoms off a dysprosium or terbium disc, which fly onto the magnet surface as a very thin film. The coated magnet is then heated in a vacuum furnace: the film melts and creeps inward along the grain boundaries — the narrow channels between the crystals — coating each grain with a tough, heat-resistant shell.
Why it matters
- Same heat resistance, far less dysprosium. Sputtered magnets typically add under 0.5% heavy rare earth by weight, instead of several percent.
- Heat resistance up, strength almost unchanged. In published trials, coercivity — the magnet's resistance to demagnetization — climbed by roughly 65–70%, while magnetic strength dropped by only a fraction of a percent.
- Lower cost. Heavy rare earths are the most expensive part of the bill; using a tenth of them changes the price tag.
One limit
The element can only creep so deep, so sputtering suits thin magnets — typically 10 mm or less. For thicker parts, manufacturers still fall back on the traditional alloying route.
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