Microstructure Origin of the Large Coercivity in an (Nd, Dy)-Fe-B Sintered Magnet
17 Pages Posted: 7 Sep 2022
(Nd,Dy)-Fe-B sintered magnets are the crucial components for elevated temperature applications in the energy sectors. However, lack of understanding on their magnetic hardening mechanism hinders the development of high-performance Dy-lean Nd-Fe-B magnets. Conventional understandings on the origin of high coercivities (Hc) in the (Nd,Dy)-Fe-B sintered magnets have stressed on the intrinsic aspects, namely the large anisotropy field (HA) of (Nd,Dy)2Fe14B compounds, while overlooking the microstructural contributions. Herein, we unveil the extrinsic origins of the large coercivities in (Nd,Dy)–Fe-B sintered magnets. Detailed characterizations on the microstructure and the magnetism of grain boundary (GB) phase reveal that 4 at.% Dy in the intergranular phase reduces its magnetization, contributing to the large coercivity of 3.32 T. This leads to a change of hardening mechanism from the pinning-type Kondorsky model for the Dy-free magnet to the nucleation-dominated Stoner-Wohlfarth model for the Dy-containing magnet. Consequently, an exceptionally large value of 40 % for Hc/HA is realized for (Nd,Dy)–Fe-B sintered magnet, two times larger than that for the Dy-free magnet. Our findings highlight that Dy in the intergranular phase plays a critical role for achieving high coercivity. This can be exploited as a strategy for microstructure engineering toward the development of Dy-lean high-performance permanent magnets.
Keywords: Permanent magnets, coercivity, (Nd, Dy)-Fe-B, magnetism of grain boundary phase, hardening mechanism
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