Adapted from an image (public domain), via Wikimedia Commons.
Carl Auer von Welsbach
Discovered praseodymium and neodymium in 1885.
Elements
Didymium was accepted as an element for over 40 years. In 1885 Carl Auer von Welsbach, in Vienna, split it into two: praseodymium, the green twin, and neodymium, the new twin.
Didymium was accepted as an element for over 40 years. In 1885 Carl Auer von Welsbach, in Vienna, split it into two: neodymium, the new twin, and praseodymium, the green twin.
Auer von Welsbach split didymium into neodymium and praseodymium. Neodymium now makes the strongest permanent magnets.
Rare-earth magnets: strength and heat
Neodymium magnets are the strongest permanent magnets there are: a small one can lift thousands of times its own weight. But they have a weakness: heat.
Same job, different sizeA magnet’s strength for its size is measured by its maximum energy product, (BH)max, in kilojoules per cubic metre: the magnetic energy it can store in each bit of its volume. To do the same job you need roughly as much less material as this number is higher. Each magnet uses the best grade of its kind.
- Ferriteiron-oxide ceramic, as in fridge magnets40 kJ/m³ · 11× the volume
- Alnicoaluminium–nickel–cobalt alloy, the strongest before the 1960s88 kJ/m³ · 5× the volume
- Samarium–cobaltthe first rare-earth magnet, from the 1960s240 kJ/m³ · 1.8× the volume
- Neodymiumneodymium–iron–boron, from 1984440 kJ/m³ · Smallest
Each magnet is drawn at the size it would need to be to hold the same weight. A neodymium magnet does the job of a ferrite one 11 times its volume, which is how headphones, phones and hard drives got so small.
Heat it up
Warm magnets get weaker. A little warmth is harmless: the strength comes back when they cool. Go past a magnet’s limit and some is lost for good; at its Curie temperature it stops being a magnet at all.
- Neodymiumstandard grade · safe to 80 °C
100%Full strength - Neodymium + dysprosiumhigh-temperature grade · safe to 230 °C
100%Full strength - Samarium–cobaltSm₂Co₁₇ · safe to 350 °C
100%Full strength
All three at full strength. Warm them up.
Where they’re used
- Small and strong
Neodymium magnets move the read head in hard drives and drive the tiny speakers in earbuds and phones: nothing else is as strong for its size.
- Motors that run hot
Electric-car motors and wind-turbine generators get warm, so their neodymium magnets often contain dysprosium or terbium. Those are rarer still, which makes the magnets costly.
- Where heat matters most
Samarium–cobalt came first, in the 1960s. It is pricier and weaker, but it works in very hot and very cold places. The hunt for something cheaper led to neodymium magnets in 1984.
Energy products, Curie temperatures and temperature coefficients from Wikipedia’s comparison tables of permanent magnets; working limits from the grade descriptions there. Real magnets vary by grade, shape and use. Past a magnet’s limit, the lasting loss is drawn starting small and growing to all of it at the Curie temperature, a simplification. Sizes assume the same job for each magnet.
Keep exploring
Where the dates and stories on this page come from; each event on the timeline links to its own source.
- Carl Auer von WelsbachEncyclopaedia Britannica
- PraseodymiumRoyal Society of Chemistry
- NeodymiumRoyal Society of Chemistry
- Carl Auer von WelsbachWikipedia