Japan Develops Magnet with A Lean Rare Earth for Motors

Sm(Fe0.8Co0.2)12 with a lean rare earth content exhibits superb magnetism. According to the report, the National Institute for Materials Science (NIMS) of Japan and Tohoku Gakuin University has developed a boron-doped anisotropic samarium Sm (Fe0.8Co0.2)12 film, the thin film containing an only small amount of rare earth elements (REEs).

The compound has a coercivity of 1.2 Tesla, which is sufficient for use in car motors. This was achieved by creating a unique granular nanostructure in which Sm(Fe0.8Co0.2)12 grains are uniformly enveloped by an amorphous grain boundary phase approximately 3 nm in thickness. This compound exhibited superior magnetic properties to that of Nd-Fe-B based magnets even when processed into a thin film.

SmFe08Co0212 with a lean rare earth exhibits superb magnetism image

Demand for green technologies that can help to reduce CO2 emissions (such as electric motors for environmentally friendly vehicles and wind power generation) has been growing, leading to a rapidly increasing demand for the high-performance permanent magnets needed for these technologies. The Nd-Fe-B based sintered magnets currently in use are composed not only of the rare earth element neodymium but also a heavy rare earth element: dysprosium.

Due to the geopolitical risks associated with obtaining such materials, it is necessary to develop new magnets that do not rely on such rare elements. Anisotropic SmFe12-based compounds containing relatively small quantities of REEs have been studied for their potential to serve as an effective alternative candidate for the next generation of permanent magnets.

In 2017, the National Institute of Materials Science of Japan confirmed that samarium-iron-cobalt compounds - Sm(Fe0.8Co0.2)12 are superior to neodymium magnets in terms of several important magnetic parameters: magnetization, magnetocrystalline anisotropy and Curie temperature. However, previous studies had found these compounds' coercivity - another important parameter for practical magnets to be inadequate.

Therefore, the research team focused on the fact that high-performance neodymium magnets with high coercivity have a multiphase microstructure, in which Nd2Fe14B microcrystals are arranged in one direction and individually enveloped by an amorphous phase approximately 3 nm in thickness. Subsequently, the research team attempted to develop a similar microstructure in which individual Sm(Fe0.8Co0.2)12grains are uniformly enclosed by a thin layer of an amorphous phase. In this research project, the group doped Sm(Fe0.8Co0.2)12 with boron, thereby fabricating a nano-granular microstructure in which Sm(Fe0.8Co0.2)12 nanoparticles are evenly surrounded by an amorphous phase approximately 3 nm in thickness.

In addition, this compound has an anisotropic granular microstructure, enabling it to exhibit a remnant magnetization greater than that exhibited by other SmFe12-based compounds with isotropic granular microstructures. As result, this compound exhibited a large coercivity of 1.2 T combined with a large remanent magnetization of 1.5 T, much larger than the previously developed SmFe12-based magnetic compounds.

This Sm(Fe0.8Co0.2)12 compound with an anisotropic, multiphase microstructure was proven to have very high coercivity, even when processed into a thin film. It may serve as a novel magnet capable of outperforming the rare earth element, neodymium magnets. Previously studied anisotropic samarium compounds exhibited significantly lower coercivity than the compound developed in this research of Japan. The underlying mechanisms which lead to realizing a high coercivity discovered in this research may apply to bulk magnets to develop practical anisotropic Sm(Fe0.8Co0.2)12 magnets with high coercivity.