Dependence of macromagnetic properties on the microstructure in high-performance Sm2Co17-type permanent magnets

Abstract

Microstructure characteristics are important for the high-performance Sm2Co17-type permanent magnets to achieve high intrinsic coercivity (Hcj) and large magnetic field at the knee-point (Hknee). In this work, the correlation between microstructures and magnetic properties has been systematically studied. The different microstructures were obtained by two procedures: by adjusting the aging temperature and optimizing the Zr content. On one hand, with increase of aging temperature from 1063 K to 1103 K, the cell size and the lamellar phase density increase from 75.1 nm and 0.014 1/nm to 101.5 nm and 0.043 1/nm, respectively, and the average peak Cu concentration at the cell boundaries reaches 21.9 at% which is helpful for obtaining relatively high Hcj and Hknee. As the aging temperature increases further to 1143 K, a much larger cell size and with incomplete cell boundaries results in an irregular distribution of Cu concentration at the cell boundaries. In this case, the Hknee is low even though the magnet shows a high Hcj. On the other hand, the increase of Zr content also promotes an increase in both the lamellar phase density and the average peak Cu concentration at the cell boundaries, giving rise to high Hcj and Hknee. Taking into consideration the aging temperature and Zr content, one can conclude that a lower aging temperature and lower Zr content produce a lower lamellar phase density and average Cu concentration at the cell boundaries and this leads to a lower Hcj and Hknee of the magnets. To further confirm this correlation between the microstructures and magnetic properties, a magnet of Sm(CobalCu0.062Fe0.285Zr0.016)7.6 was aged at a higher temperature of 1143 K to increase the lamellar phase density. As expected, the lamellar phase density increases from 0.008 to 0.013 1/nm; however, the cell size increases simultaneously from 142.5 to 247 nm. The magnet exhibits a much higher but uneven Cu concentration at the cell boundaries. As a result, the Hcj increases from 1.64 to 10.18 kOe, while Hknee just increases from 1.09 to 3.91 kOe.