Magnetic performance change of multi-main-phase Nd–Ce–Fe–B magnets by diffusing (Nd, Pr)H_x

Abstract

The grain boundary diffusion process (GBDP) is effective to enhance coercivity of the singlemain-phase (SMP) RE 2 Fe 14 B (rare earth (RE)) magnets through forming magnetic hardening shells surrounding the hard grain cores. Here, the GBDP was applied to the multi-main-phase (MMP) (Nd, Pr) 22.3 Ce 8.24 Fe bal M 1.0 B 1.0 (wt.%) magnets prepared by sintering the mixture of Ce-free and Ce-containing 2:14:1 powders, which have shown superior magnetic properties, especially coercivity, to the SMP ones at the same average composition. The remanence of the (Nd, Pr)H x diffused magnets increases gradually with the increase of diffusion temperature from 480 to 880 °C, the coercivity, however, slightly decreases. The highest (BH) max of 350.1 kJ m −3 is achieved when diffusing at 680 °C, which is 9.2% higher than 320.7 kJ m −3 for the as-prepared magnet. The remanence increment is due to the diffusion of Nd/Pr into the 2:14:1 phase grains, enlarging the intrinsic saturation magnetic polarization. The slight coercivity reduction is due to the gradual homogenization of RE distribution within the 2:14:1 grains of the undiffused parts, i.e. approaching the 'close to equilibrium (or SMP)' state, which offsets the positive contributions from the enrichment of Nd/Pr in the Ce-rich 2:14:1 phase and the formation of continuous RE-rich intergranular phase. These findings suggest that the GBDP effect on coercivity of the MMP Nd-Ce-Fe-B magnets is distinctly different from the SMP ones, and that the chemical heterogeneity should be carefully controlled to improve the magnetic properties of such high cost-performance permanent magnets.

Micromagnetic simulation of microstructure effect for binary-main-phase Nd–Ce–Fe–B magnets

“…When the Ce concentration is large ( 30%), the coercivity drastically changes with δ Nd . It is not desirable to achieve high coercivity with a large Ce concentration ( 30%) because it is difficult to measure or control shell thickness experimentally [3]. On the other hand, when the substituted Ce concentration is low ( 20%), the variation in coercivity with δ Nd is small.…”

“…magnets resulted in the imbalance of resource utilization and inevitable price hike. Thus, considerable attention has been focused on developing high cost-performance Nd-Fe-Bbased magnets where Nd element is substituted by cheap and abundant rare-earth elements such as Ce and La [1][2][3][4]. Unfortunately, earlier reports showed that chemically homogeneous, single-main-phase (SMP) Nd-Ce-Fe-B magnets usually suffer from severe deterioration in magnetic properties [5,6].…”

Insight into the Property Enhancement Mechanism of Chemically Prepared Multi-Main-Phase (Nd,Ce)2Fe14B

“…In addition, there seems to be a lot of room for the property enhancement of the MMP (Nd,Ce) 2 Fe 14 B magnets because the theoretical coercivity of Nd 2 Fe 14 B is about 70 kOe. 25,26 In addition, although several research studies attempted to prepare high-performance Nd 2 Fe 14 B nanostructures, no chemical process was applied for the high-abundance rare-earth doping into Nd 2 Fe 14 B. 27−30 We have developed a chemical process based on ball milling and reductive annealing to synthesize high-performance Nd 2 Fe 14 B nanostructures as magnetic units in previous work, showing an obvious coercivity enhancement of the Nd 2 Fe 14 B powders, which provides a promising way for the synthesis of Ce-doped Nd 2 Fe 14 B nanostructures by the chemical process and the property enhancement of MMP (Nd,Ce) 2 Fe 14 B nanomagnets.…”

“…However, the magnetic features of the grain boundary phase as well as the difference with the SMP sample are not fully clear. In addition, there seems to be a lot of room for the property enhancement of the MMP (Nd,Ce) 2 Fe 14 B magnets because the theoretical coercivity of Nd 2 Fe 14 B is about 70 kOe. , In addition, although several research studies attempted to prepare high-performance Nd 2 Fe 14 B nanostructures, no chemical process was applied for the high-abundance rare-earth doping into Nd 2 Fe 14 B. − …”

Role of lanthanum in microstructure evolution and enhanced magnetic properties of cerium‐containing sintered magnets

“…Tremendous market demands for Nd 2 Fe 14 B-based per-manent magnets have caused the overuse of neodymium/praseodymium, and consequently result in the redundance of lanthanum and cerium. In recent years, the high abundance rare earth elements have brought out extensive attention on partial substitution of neodymium/praseodymium in REÀ FeÀ B magnets [6][7][8][9][10]. Many efforts have been made to enhance the performance of lanthanum/cerium-added magnets by various researchers [11][12][13][14].…”