NIMS' Magnet Cheaper, Higher-performance Than Nd Magnets

- Apr 10, 2019-

Japan's National Institute for Materials Science (NIMS) succeeded in synthesizing a new magnet that contains less Nd (neodymium, rare earth material) and has higher magnetic properties than Nd2Fe14B (Nd magnet), which is currently the most powerful magnet in the world.

This was announced Oct 20, 2014. The composition of the new magnet is Nd2Fe12Nx.

The anisotropy field, which is proportionate to coercive force (the strength of opposing magnetic field, which causes the loss of magnetic force), of the new magnet material is about 8T (tesla) at room temperatures. And its saturation magnetization (ability to output magnetic force) is 1.66T with a margin of error of ±5%. The anisotropy field is higher than that of a Nd magnet (about 7T), and the saturation magnetization is equivalent to that of a Nd magnet (about 1.6T).

In addition, when the temperature of the material keeps rising, its saturation magnetization decreases less than that of a Nd magnet. Therefore, under high temperatures, its saturation magnetization is superior to that of a Nd magnet. The Curie point (at which magnetization is lost) of the new material is about 550°C, which is more than 200°C higher than that of a Nd magnet (312°C). The new material is expected to be used for hybrid electric vehicles (HEVs), which need to use a motor under high temperatures.

The content ratio of Nd in the new magnet material (Nd2Fe12Nx, x=1) is 17% by weight, which is very small, compared with a Nd magnet (about 27%). Furthermore, the new material enables to use N (nitrogen), which is inexpensive, in place of B (boron), which is contained in Nd magnets and relatively expensive, giving it an edge in terms of resource use and cost.

However, NIMS made a thin film this time, not a sintered magnet called bulk. Therefore, it is not possible to replace existing sintered Nd magnets with the new magnet anytime soon. It is necessary to make powder of the new magnet material and conduct a research to sinter the powder.

The thin film was made in the following way. First, tungsten (W), whose crystal lattice has an interval similar to NdFe12 compound, is grown on a monocrystalline substrate made of MgO. Then, NdFe12 is stabilized by using the heteroepitaxial growth of W. Finally, by heating NdFe12in a nitrogen atmosphere, the Nd2Fe12Nx thin film is synthesized. The thickness of the film is 350nm.