Among the various permanent magnets reported to date, FeNdB exhibits the highest magnetic performance, but reducing the use of the rare‐earth elements is necessary to avoid exhaustion of rare‐earth elements. The key to improve the performance of permanent magnets is to increase magnetization and coercivity. FeCo has a very large magnetization, but has a very small coercivity caused by the extremely small magnetic anisotropy due to the cubic crystal structure, so that FeCo has long been unsuitable for permanent magnets. However, recent reports have revealed that the transformation of the crystal structure from cubic to tetragonal causes large magnetic anisotropy. In 2017, the author reported that a large coercivity can be obtained by fabricating tetragonal FeCo nanodots. This article reviews recent progress of rear‐earth free permanent magnets especially for the tetragonal FeCo based alloys.

中文翻译：

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研发无稀土的FeCo基永磁体面临的挑战

在迄今为止报道的各种永磁体中，FeNdB表现出最高的磁性能，但为避免耗尽稀土元素，必须减少稀土元素的使用。改善永磁体性能的关键是增加磁化强度和矫顽力。FeCo具有很大的磁化强度，但是由于立方晶体结构由于极小的磁各向异性而导致的矫顽力非常小，因此FeCo长期以来不适合于永磁体。但是，最近的报道表明，晶体结构从立方到四方的转变引起大的磁各向异性。在2017年，作者报告说，通过制造四方FeCo纳米点可以获得较大的矫顽力。