Microstructure, coercivity and thermal stability of nanostructured (Nd,Ce)-(Fe,Co)-B hot-compacted permanent magnets

Joint publication of CRC/TRR 270 and partners from Beihang University (China)


Y. Wu, K. P. Skokov, L. Schäfer, F. Maccari, A. Aubert, H. Xu, H. Wu, C. Jiang, O. Gutfleisch

Acta Materialia, 235, 118062 (2022).

We report on microstructure, hard magnetic properties and thermal stability of nanocrystalline (Nd0.85Ce0.15)15(Fe1-xCox)78B7 (x = 0 – 1) hot-compacted permanent magnets. At lower Co concentrations (x < 0.3), the substitution of Fe by Co changes the composition of grain boundary phase from non-magnetic (Nd,Ce)2Fe1 to magnetic (Nd,Ce)1(Fe,Co)2, leading to the degrading of the coercivity. At x ≥ 0.6, the grain boundary phase is no longer observed between the nanocrystalline grains, resulting in strong magnetic coupling of constituent phases. With the further increase of Co concentration (x>0.6), additional RE(Fe,Co)2, RE(Fe,Co)4B and RECo5 phases are gradually formed in the magnets. A new type of microstructure with nanograins of RE2(Fe,Co)14B phase, RE(Fe,Co)2 phase and RE(Fe,Co)4B phase, with partial or without grain boundary phase shows good thermal stability (x = 0.4 and 0.6). In (Nd0.85Ce0.15)15(Fe0.4Co0.6)78B7 magnets, the absolute values of temperature coefficient of coercivity can reach 0.3 %/K within the temperature range of 300 K – 500 K, and it exceeds 0.23 %/K for the temperature range of 300 K – 650 K, indicating a promising method for designing highly thermal stable permanent magnets.

DOI: 10.1016/j.actamat.2022.118062