With the advent of high-flux density permanent magnets based on rare earth elements such as neodymium (Nd) in the 1980s, permanent magnet-based electric machines had a clear performance and cost advantage over induction machines when weight and size were factors such as in hybrid electric vehicles and wind turbines. However, the advantages of the permanent magnet-based electric machines may be overshadowed by supply constraints and high prices of their key constituents, rare earth elements, which have seen nearly a 10-fold increase in price in the last 5 years and the imposition of export limits by the major producing country, China, since 2010. We outline the challenges, prospects, and pitfalls for several potential alloys that could replace Nd-based permanent magnets with more abundant and less strategically important elements.
The mandate to reduce greenhouse gases will require highly efficient electric machines for both power generation and traction motor applications. Although permanent magnet electric machines utilizing Nd 2 Fe 14 B-based magnets provide obvious power-to-weight advantages over induction machines, the limited availability and high price of the rare earth (RE) metals make these machines less favorable. Of particular concern is the cost and supply criticality of Dy, a key RE element that is required to improve the high-temperature performance of Nd-based magnetic alloys for use in generators and traction motors. Alternatives to RE-based alloys do exist, but they currently lack the energy density necessary to replace Nd-based magnets. Many of these compounds have been known for decades, but serious interest in their development waned once compounds based on RE elements were discovered. In this review, intrinsic and extrinsic materials factors that impact the optimization of both existing and potential future permanent magnets for energy applications are examined in light of new insights gained from renewed examination.
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