Toyota Motor Corporation has developed the world’s first neodymium-reduced, heat-resistant magnet. Neodymium (Nd) magnets are used in various types of motors such as the high-output motors found in electrified vehicles. The new magnet uses significantly less neodymium, a rare-earth element, and can be used in high-temperature conditions.
The newly developed magnet uses no terbium (Tb) or dysprosium (Dy)—rare earths that are also categorized as critical materials necessary for highly heat-resistant neodymium magnets. 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.
Accordingly, Toyota adopted new technologies 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 earlier neodymium magnets, while reducing the amount of neodymium used by up to 50%.
The newly developed Nd-reduced, heat-resistant magnet is able to maintain coercivity even at high temperatures because of the combination of the following three new technologies:
Grain refinement of magnet. It is now possible to retain high coercivity at high temperatures through the reduction of the size of the magnet grains to one-tenth or less of those found in conventional neodymium magnets and the enlargement of the grain boundary area.
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. Thus, it is possible to efficiently use neodymium by increasing the neodymium concentration on the surface of the magnet grains, which is necessary to increase coercivity, and decreasing the concentration in the grain core. This results in the reduction of the overall amount of neodymium used in the new magnet.
Specific ratio of lanthanum and cerium. If neodymium is simply alloyed with lanthanum and cerium, its performance properties (heat resistance and coercivity) decline substantially, complicating the use of light rare earths. As a result of the evaluation of various alloys, Toyota discovered a specific ratio at which lanthanum and cerium, both abundant and low-cost rare earths, can be alloyed so that the deterioration of properties is suppressed.
Toyota expects this new type of magnet to be useful in expanding use of motors in various areas such as automobiles and robotics, as well as maintaining a balance between the supply and demand of valuable rare earth resources. Toyota will work to further enhance performance and evaluate application in products while accelerating the development of mass production technologies, with the aim of achieving early adoption in motors used for various applications, including in automobiles and robotics.
Background. Magnets used in automotive motors and other applications have high coercivity (the ability to maintain magnetization) even at high temperatures. For this reason, approximately 30% of the elements used in magnets are rare earths.
When powerful neodymium magnets are used at high temperatures—e.g., for automotive applications—terbium and dysprosium are generally added to increase high-temperature coercivity. However, terbium and dysprosium are rare and expensive metals found in locations with high geopolitical risks. Because of this, considerable efforts have been made to develop magnets that do not use these metals.
Production volumes of neodymium are relatively high among rare earths, but there are concerns that shortages will develop as electrified vehicles, including hybrid and battery electric vehicles, become increasingly popular in the future.
This research and development initiative was conducted as part of the “Development of Magnetic Material Technology for High-efficiency Motors for Next-Generation Automobiles” report issued by the New Energy and Industrial Technology Development Organization (NEDO).
Future Efforts. Going forward, Toyota will proceed with further practical use in mind, perform application assessments in motor vehicles, and continue researching and developing technologies with the aim of low-cost, stable production. Toyota expects that the magnets will be put to use in the motors of electric power steering for automobiles and other applications in the first half of the 2020s.
Furthermore, the company will undertake development with the aim of practical application in high-performance electrified vehicle drive motors within the next 10 years.
This research and development initiative was conducted as part of the "Development of Magnetic Material Technology for High-efficiency Motors for Next-Generation Automobiles" report issued by the New Energy and Industrial Technology Development Organization (NEDO).