Getting Geeky: Building a Better Magnet

You don’t think of Toyota as a company likely to be in the business of inventing new kinds of magnets, but permanent magnets are an important element of hybrid and electric cars. And there’s been an interesting development.

Right now, the best magnets follow are the standard iron, boron, neodymium (NdFeB) magnet. NdFeB magnets are able to produce a strong magnetic field in small volumes. When paired with dysprosium, NdFeB magnets also have high coercivity, that is, the ability to resist demagnetization once magnetized. More ordinary permanent magnets lose the strength of their magnetic field when heated; NdFeB-dysprosium magnets are much less susceptible to hear degradation of their magnetic field.

But rare earth elements like neodymium and dysprosium are expensive, and supplies are largely controlled by the Peoples Republic of China.  China threatened to stop exporting neodymium and other rare earths in 2011, which sent prices for the metals soaring. If China were to use rare earth elements as a geopolitical tool again, it could significantly impact companies like Toyota.

Toyota’s new magnets use 20-50% of the neodymium as traditional NdFeB magnets. They substitute instead much less expensive rare earths lanthanum and cerium.  Reuters notes that while neodymium costs about $100 per kg and dysprosium costs about $400 per kg, lanthanum and cerium cost about $5 to $7 per kg. A cheaper formulation means a less expensive magnet. A less expensive magnet could result in cheaper hybrid and all-electric vehicles.

In addition to substitution of elements, Toyota found a few other tricks to create less expensive, more coercive magnets.

Instead of magnets with a uniform concentration of neodymium, Toyota's magnets concentrate neodymium around the edges of the magnet.

Instead of magnets with a uniform concentration of neodymium, Toyota’s magnets concentrate neodymium around the edges of the magnet.

Toyota reportd says that simply replacing the neodymium in a magnet with lanthanum and cerium results in a sub-par magnet with reduced coercivity and reduced heat resistance, meaning motor performance will suffer. Instead, the company composed the magnet so that most of the lanthanum and cerium grains were internal to the magnet, and most of the neodymium grains were on the outside. Less neodymium, and what is used concentrated in an optimum area.

Science and technology breakthroughs are important, but most progress is incremental, comparatively small changes that have great cumulative effect. Toyota’s improvements to NdFeB batteries are a classic example.