Intrinsic evolution of novel (Nd, MM)2Fe14B-system magnetic flakes
The Nd-substituted (Nd x MM1−x )–Fe–B strip-casting flakes were prepared by induction melting in the vacuum furnace and then subsequently by strip-casting technology. The microstructure and magnetic properties of (Nd x MM1−x )–Fe–B alloys are related to the Nd substitution. 2:14:1 main phases and minor impure phases coexist in the MM–Fe–B flake. For example, La2O3 and CeFe2 impure phases are obviously detected in the x = 0 specimen. As an increase of the Ce concentration is inversely accompanied with the decrease of the Nd content (x) in (Nd x MM1−x )2Fe14B main phases (0 ≤ x ≤ 1), XRD analysis shows that the overall diffraction peaks of the main phases shift to right domestically because of smaller radius Ce4+. The melting point, spin reorientation phase transition temperature, Curie temperature, magneto-crystalline anisotropy field (at 300 K), and the magnetization (M 9T) for MM–Fe–B/(Nd0.4MM0.6)–Fe–B/(Nd0.7MM0.3)–Fe–B/Nd–Fe–B strip-casting alloys are 1376.15/1414.15/1439.15/1458.15 K, 74/113/124/135 K, 493.2/538.4/559.7/582.3 K, 48/55.2/64.4/70.1 kOe and 136.5/143.7/151.5/153.7 emu/g, respectively. Due to the varied composition of hard magnetic main phases, M 9T increases gradually with the increase of Nd content (x). SEM observation and EDX results demonstrate that more Nd and Pr elements aggregate into the 2:14:1 ferromagnetic phase, while less La and Ce elements are prone to the RE-rich region compared with the nominal ratio. As a result, the growth of M 9T becomes extraordinary under maximum external field 9 T, indicating that the (Nd0.7MM0.3)–Fe–B flake may display relatively good magnetic properties and those with higher Nd content have evident effect on magnetization, compositions, and microstructures of hard magnetic main phases. Therefore, practical application of (Nd x MM1−x )–Fe–B-sintered magnets will be very prospective.
This work was supported by the Major State Basic Research Development Program of China (973 Program) (2014CB643701), National Natural Science Foundation of China (51571064, 51331003, and 51371002), National Key Research and Development Program of China (2016YFB0700902), International S&T Cooperation Program of China (2015DFG52020), and the 2011 Cooperative Innovation Center of Beijing University of Technology.
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