Improved Coercivity in Cu-Doped SmCo5 Nanocomposite Powders Obtained by Low Temperature Annealing

doi:10.1007/s40195-025-01827-z

Abstract

Abstract:

In this work, nanocrystalline SmCo₅-Cu nanocomposite powders were fabricated from the ball-milled amorphous matrix by crystallization annealing which is lower than the traditional sintering temperature ~ 1000 °C for bulk SmCo₅ bulk magnets. Annealed Cu-doped SmCo₅ powders have a higher coercivity compared to that of Cu-free SmCo₅ one due to the combined effects of refinement effect of grain size and the pinning effect induced by Cu doping. The peak of coercivity (H_c) is located at 600 °C for annealed Cu-doped SmCo₅, which is ascribed to the improved pinning field. The pinning effect became reduced when the annealing was done at even higher temperatures. More importantly, the best comprehensive magnetic properties, including a maximum magnetic energy product (BH)_max of 12.2 MGOe together with a coercivity of 31.8 kOe and a remanence of 64.3 emu/g, could be achieved for SmCo₅-3 wt% Cu by low temperature annealing. These results demonstrate that isotropic Cu-doped SmCo₅ nanocrystalline powders are promising precursors for the fabrication of high-performance bulk magnets.

Key words: Rare earth permanent magnet, SmCo₅, Nanocrystalline, Refinement, Pinning mechanism, Crystallization

Longfei Ma, Yingzhengsheng Huang, Wei Quan, Qiang Zheng, Juan Du. Improved Coercivity in Cu-Doped SmCo₅ Nanocomposite Powders Obtained by Low Temperature Annealing[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(4): 587-596.

Figures/Tables 7

Fig. 1 Intrinsic coercivity Hci (T) a and the change of coercivity ΔHci (T) of different Cu doping compared with that of Cu-free SmCo5 b. The first derivative of the initial magnetization curves (dM/dH) for SmCo5-3 wt% Cu annealed at different temperatures c and SmCo5 containing different Cu contents annealed at 600 °C d. The initial magnetization curves of c, d are shown as insets

Table 1 Magnetic properties, including coercivity Hci, remanence Mr, maximum magnetic energy product (BH)max of different weight percent of Cu-doped SmCo5 annealed at different temperatures for 30 min

Cu doping (wt%)	Temperature (°C)	H_ci (kOe)	ΔH_ci (kOe)	M_r (emu/g)	(BH)_max (MGOe)
0	500	19.7		75.8	15.9
1	500	22.8	3.1	70.3	14.0
3	500	26.0	6.3	66.4	12.5
5	500	24.8	5.1	63.1	11.2
0	550	25.5	-	70.7	13.8
1	550	28.1	2.6	69.4	13.4
3	550	31.8	6.3	64.3	12.2
5	550	31.4	5.9	59.2	11.2
0	600	26.1	-	66.6	12.2
1	600	31.7	5.6	65.4	11.7
3	600	34.2	8.1	59.7	10.1
5	600	33.6	7.5	54.3	9.2
0	650	28.5	-	62.9	11.1
1	650	31.4	2.9	62.5	9.9
3	650	32.5	4	56.8	8.2
5	650	32.1	3.6	52.5	7.9

Fig. 2 XRD patterns of different Cu doped SmCo5 annealed at 600 °C for 30 min a, b the calculated grain size by Scherrer formula for SmCo5 containing different Cu contents annealed at different temperatures for 30 min

Fig. 3 Demagnetization curves of SmCo5 containing 0 and 1 wt% Cu annealed at 600 °C a, the demagnetization curves of SmCo5 containing 1 wt% Cu annealed at different temperatures b, the relationship between remanence c, maximum magnetic energy product (BH)max d and annealing temperatures for SmCo5 containing different Cu contents

Fig. 4 XRD patterns of SmCo5 containing 1 wt% Cu annealed at different temperatures for 30 min

Fig. 5 TEM image of the SmCo5-1 wt% Cu annealed at 600 °C for 30 min a, STEM image of the SmCo5-1 wt% Cu annealed at 600 °C for 30 min b and the corresponding elemental maps for Sm c, Co d, Cu e, respectively

Fig. 6 Line scanning of three elements, Sm, Co and Cu a, the ratio of (Co + Cu)/Sm along the scanning line b for SmCo5-3 wt% Cu annealed at 600 °C for 30 min. The image of the line scanning results is shown in a

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Improved Coercivity in Cu-Doped SmCo₅ Nanocomposite Powders Obtained by Low Temperature Annealing

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