Grain boundary optimization induced substantial squareness enhancement and high performance in iron-rich Sm-Co-Fe-Cu-Zr magnets

doi:10.1016/j.jmst.2020.12.067

Abstract

Abstract:

Increasing iron content has been witnessed an essential method to improve the remanence of 2:17-type Sm-Co-Fe-Cu-Zr magnets, however, the inferior squareness factor accompanied with the increased iron content turns into a neck sticking problem. In this work, the grain boundary optimization induced substantial squareness enhancement from 63.4% to 91.4%, and consequently an excellent maximum energy product of 32.63 MGOe have been achieved in iron-rich Sm-Co-Fe-Cu-Zr magnets via tuning solution process. It is clearly revealed that the grain boundary (GB) phases as well as the micro-twins’ density in grain interiors can be controlled and interprets the enhancement mechanism of squareness.

Key words: Iron-rich, Sm-Co-Fe-Cu-Zr magnet, Grain boundary, Squareness

Jun Cao, Tianli Zhang, Jinghua Liu, Hao Xu, Mingyao Hu, Wei Xia, Ao Wang, Hui Wang, Chengbao Jiang. Grain boundary optimization induced substantial squareness enhancement and high performance in iron-rich Sm-Co-Fe-Cu-Zr magnets[J]. J. Mater. Sci. Technol., 2021, 85: 56-61.

Figures/Tables 6

Fig. 1. The demagnetization curves for magnets A and B (a); XRD pattern of the solution precursors of Pre-Magnet A and Pre-Magnet B (b); back-scattered SEM images of the solution precursors of Pre-Magnet A (c) and Pre-Magnet B (d).

Table 1 Magnetic properties of the two kinds of final magnets.

Sample	(BH)_max (MGOe)	B_r (kGs)	H_cj (kOe)	SF (%)
Magnet A (Conventional Process 1)	30.90	11.94	15.14	63.4
Magnet B (Optimized Process 2)	32.46	11.94	15.17	91.0

Fig. 2. SEM images and high magnification of magnet A (a, c) and magnet B (b, d); elements distribution across the GBs for magnet A (e) and magnet B (f), respectively. Insets in (a) and (b) show the corresponding grain size distribution.

Fig. 3. Bright-field images for final magnets along [001]-2:17R zone-axis (A -(a) and B-(b)) and [210]-2:17R zone-axis (A-(c) and B-(d)), the insets are the corresponding SAED patterns. TEM-EDS line scan across the cell boundaries along the orange lines marked in (e) and (f), where (e) and (g) for magnet A, (f) and (h) for magnet B.

Fig. 4. HRTEM images for magnet A (a, b) and magnet B (c, d) along [100]-2:17R zone-axis. The Figs. 1-3 are the FFT patterns for the marked regions in (a) and (b).

Fig. 5. Initial magnetization curves for magnets A and B (a), inset is the corresponding susceptibility curves at room temperature. The plots of Hcj1/2 vs. T2/3 for magnets A and B over the temperature range 25-300 °C (b).

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