Magnet for electric motors cuts rare earth use by half

February 22, 2018 // By Nick Flaherty
Toyota has developed the world's first heat resistant motor that custs the use of the neodymium rare earth element in half.

Neodymium magnets are used in high output motors in electrified vehicles, with up to 30% of the magnet using costly rare earth elements. The new magnet uses significantly less neodymium and can be used in high-temperature conditions.

The newly developed magnet uses no terbium (Tb) or dysprosium (Dy), which are rare earths that are considered as critical for heat-resistant neodymium magnets but are often sourced from locations with high geopolitical risks. A portion of the neodymium has been replaced with lanthanum (La) and cerium (Ce), which are low-cost rare earths, reducing the amount of neodymium used in the magnet.

Neodymium plays an important role in maintaining high coercivity (the ability to maintain magnetization) and heat resistance. Merely reducing the amount of neodymium and replacing it with lanthanum and cerium results in a decline in motor performance. Instead, Toyota used new techniques that suppress the deterioration of coercivity and heat resistance, even when neodymium is replaced with lanthanum and cerium, and developed a magnet that has equivalent levels of heat resistance as the previous generation using half the amount of neodymium.

The magnet is able to maintain coercivity even at high temperatures because of the combination of reducing the magnetic grain to 10% of previous designs and a two-layered high-performance grain surface. In a conventional neodymium magnet, neodymium is spread evenly within the grains of the magnet, and in many cases, the neodymium used is more than the necessary amount to maintain coercivity. Increasing the neodymium concentration on the surface of the magnet grains, and decreasing the concentration in the grain core, reduces the total amount of the element needed. This is combined with a specific ratio of lanthanum and cerium as an alloy to maintain the performance of the magnet.

The magnet is expected to be used in electric cars for drive motors and generators, electric power steering, robots, and various household appliances. It will also contribute to reducing the risks of a disruption in supply