Structure and Thermal Stability of a Bulk Nanocrystalline ${\hbox {Sm}}_{0.8}{\hbox {Tm}}_{0.2}{\hbox {Co}}_{5.2}$ Permanent Magnet

The structure and thermal stability were studied for bulk nanorcystalline Sm_0.8Tm_0.2Co_5.2 permanent magnets produced by spark plasma sintering technique. X-ray diffraction results show that the magnet exhibits CaCu₅ crystal structures. Transmission electron microscopy observation indicates that the microstructure of the magnet was composed of fine and uniform grains with an average size of about 50 nm. Magnetic measurement shows that the Curie temperature ( TC) of the magnet is 983 K, the magnetization and the remanence (Mr) under 9 T of the magnet are 71.72 and 47.82 emu/g, respectively, and the coercivity (Hci) of the magnet reaches as high as 25.70 kOe. Moreover, the Mr of the magnet keeps almost invariant as the temperature increases from 373 K to 573 K, and the Mr and Hci temperature coefficient in the range of 373 K-773 K are -0.082%/K and -0.144%/K, demonstrating the excellent thermal stability of the magnet.