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 found to have the TbCU7-tYPe structure. The c/a ratio decreases with increasing Ti concentration x, but the unit cell volume increase with x. A minor amount 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 exceeds 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 decomposed 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-milled 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 coercivity of 2.5T was found for the ball-milled SmCo6.6Ti0.4 magnet. The high coercivity of the ball-milled SMCo7-xTix magnets is attributed to the strong pinning of the walls of the 'interaction domains' by the network of grain boundaries between the nanocrystalline grains. (C) 2001 Elsevier Science B.V. All rights reserved.