The Origin of Coercivity Enhancement of Sintered NdFeB Magnets Prepared by Dy Addition

Abstract

The effect of Dy addition on the microstructure and magnetic properties of the sintered NdFeB magnets was investigated. The results of the microstructure analysis showed that Dy-free and Dy-doped samples are composed of Nd 2 Fe 14 B (P42/mnm) and a trace of Nd-rich phase. Dy addition reduces significantly the pole density factor of (004), (006) and (008) crystal faces as estimated by the Horta formula. Accordingly, the coercivity of the Dy-doped sample increases from 2038 kA·m −1 up to 2288 kA·m. The H cj (T)/M s (T) versus /M s (T) (Kronmüller-plot) behavior shows that the nucleation is the dominating mechanism for the magnetization reversal in these two kinds of magnets, and two microstructural parameters of α k and N eff are obtained. The Kronmüller-Plot gives evidence for an increase of the α k responsible for an increase of the coercivity as the result of the increase of the magnetic field as the magnetic domain reversed.

Determination of Dy substitution site in Nd2−xDyxFe14B by HAADF-STEM and illustration of magnetic anisotropy of “g” and “f” sites, before and after substitution

“…Current maximum coercivity of unsubstituted Nd 2 Fe 14 B is recorded as 10 kOe, which makes it economically inadequate for commercial purpose. However, magnetic properties of Nd 2 Fe 14 B have been improved significantly by the substitution of Nd with rare earth elements (RE) 12 – 21 . Hence the synthesis of Nd 2−x RE x Fe 14 B by RE substitution for Nd is vital for the applications of Nd 2 F e14 B on commercial scale.…”

Coercivity Mechanism of (Nd0.8Ce0.2)2.4Fe12Co2B Ribbons with Ferromagnetic Grain Boundary Phase

“…The parameters α k = 0.67 and N eff = 0.58 of melt-spun (Nd 0.8 Ce 0.2 ) 2.4 Fe 12 Co 2 B ribbons do differ markedly from 0.25 and 0.26 observed in the melt-spun Nd-Fe-B ribbons [32]. The large value of α K and small value of N eff are helpful for the enhancement of the coercive field in the NdFeB materials [33]. In Table 1, parameter α K is 0.67 and 0.66, and is almost the same for the melt-spun sample and the annealed sample.…”

Determination of Dy Substitution Site in Nd2-xDyxFe14B by HAADF-STEM and Illustration of Magnetic Anisotropy of “g” and “f” Sites, Before and After Substitution

“…However, magnetic properties of Nd 2 Fe 14 B have been improved signi cantly by the substitution of Nd with rare earth elements (RE). [12][13][14][15][16][17][18][19][20][21] Hence the synthesis of Nd 2 − x RE x Fe 14 B by RE substitution for Nd is vital for the applications of Nd 2 F e14 B on commercial scale. The site of RE atoms in the Nd 2 −…”