Magnetic and structural properties of SmCo7-xTix magnets

The main phase in as-east SMCo7-xTix (x = 0.3, 0.4 0.5, 0.6) magnets is fou nd to have the TbCU7-tYPe structure. The c/a ratio decreases with increasin g Ti concentration x, but the unit cell volume increase with x. A minor amo unt of a rhombohedral Th2Zn17-type phase was detected at x = 0.3, 0.4, and an another Ce2Ni7-type phase with low Curie temperature appeared when x exc eeds 0.5. No more than 0.1 T of intrinsic coercivity was obtained in the as -east samples. After annealing, the TbCU7-tYPe SMCo7-xTix magnets decompose d into 1 : 5 and 2:17 phases, with a slight increase in coercivity compared with the corresponding as-cast samples up to a maximum of 0.24T. The as-mi lled amorphous SMCo7-xTix magnets recrystallised with TbCu7-type structure after annealing at 750 degreesC for 2h. High intrinsic coercivities of more than 2.0T were obtained for almost all compositions, and maximum coercivit y of 2.5T was found for the ball-milled SmCo6.6Ti0.4 magnet. The high coerc ivity of the ball-milled SMCo7-xTix magnets is attributed to the strong pin ning of the walls of the 'interaction domains' by the network of grain boun daries between the nanocrystalline grains. (C) 2001 Elsevier Science B.V. A ll rights reserved.