Mechanism of the enhanced coercivity for the dual-main-phase Ce–Fe–B magnet

Abstract

The high coercivity of Nd–Fe–B magnets can also be obtained in the Ce–Fe–B magnets fabricated via the dual-main-phase (DMP) method in which the high abundance Ce was used to substitute Nd(Pr). The inhomogeneous distributions of the matrix grains in the DMP magnet play a key role in the enhanced magnetic performance. Compared with the single-phase magnet, more grain boundary phases encapsulating the matrix 2:14:1 grain are formed in the DMP magnet, which reduce the exchange coupling between adjacent magnetic grains. The switching field distribution and the interaction field distribution of the Ce–Fe–B magnets were determined by the first-order-reversal curves (FORC). The switching field peaks around 6 kOe, 11 kOe and 12 kOe in the FORC distribution indicate that three major reversal components coexist for the DMP magnet. The overlapp of the second and third switching field peaks reveals the presence of a pinning interaction within individual magnetic grains with a core–shell structure, which further improve the coercivity of the magnet.

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

“…As shown in figures 2 and 4(a), the simulation offers (BH) max ∼ 340 kJ m −3 (42.5 MGOe) and H cj ∼ 0.78 MA m −1 (9.8 kOe) for 40% Ce and δ Nd = 30 nm. Consequently, the simulated results demonstrate superior magnetic properties of BMP magnets over SMP magnets, in good agreement with the experimental results [13,20].…”

“…The BMP magnet shows a large energy product that approaches ideal permanent magnets. The significant differences in coercivity and maximum energy product for the BMP and SMP magnets are found at any Ce concentration, in good agreement with experimental results [9,20]. Furthermore, the micromagnetic simulation reveals the different routes of magnetization reversal for the BMP and SMP magnets.…”

“…Figure 7(a) shows the variation in coercivity with increasing the GB thickness for some representative Nd-rich shell thicknesses (5 nm, 15 nm, and 30 nm). The GB thickness is varied from 10 nm to 40 nm, taking account of experimentally measured GB thickness [9,20]. For any Nd-rich shell thicknesses, as the GB thickness increases, the coercivity tends to increase.…”

“…Taking into account experimental results for the GB phase [9,20], the GB thicknesses required for the simulation are set to 10 nm and 3 nm for the BMP and SMP magnets, respectively. The thickness of the Nd-rich shell, δ Nd , varies from 5 nm to 30 nm.…”

“…Another key of GB restructuring consists in a thick thickness of GB layer. The thickness of GB layer is usually 10-40 nm [18,20], much wider than the exchange length of Nd 2 Fe 14 B phase, 4.2 nm [21]. Due to the thick GB layer, the intergrain exchange coupling is very weak, and the magnetostatic interaction is dominant among the grains [14].…”