Magnetic properties and microstructure of SmCo5+α-Fe nanocomposite magnets prepared by mechanical alloying

Preparation of nanocomposite permanent magnets composed of SmCo5 as a hard magnetic phase and alpha -Fe as a soft magnetic phase has been tried by mechanical alloying of a mixture of SmCo5 and alpha -Fe powders and subsequent heat treatment for crystallization. The amount of the soft alpha -Fe phase was varied, and the effects of Fe content on the magnetic properties have been investigated. The mechanically alloyed (SmCo5)(1-x)Fe-x powders were found to be composed of the Sm-Co amorphous phase and the alpha -Fe phase. The composite of a SmCo5 phase (1-5 phase) and an alpha -Fe phase obtained by heat treatment at 823 or 873 K. On the other hand, after crystallization at 923 or 1073 K, the 2-17 phase was formed instead of the 1-5 phase. The (SmCo5)(1-x)Fe-x powders crystallized at 873 K showed fine microstructures composed of grains 10-20 nm in size. The values of remanence Mr of the (SmCo5)(1-x)Fe-x powders significantly increased with increasing Fe content, on the other hand, the values of coercivity linearly decreased. The maximum value of maximum energy product (BH)max, 105.8 kJ/m(3), was obtained for the (SmCo5)(75)Fe-25 powder. In the demagnetization curves of the (SMCo5)(1-x)Fe-x powders in the second quadrant, any step due to the presence of soft phases was not detected and the recoil loops showed a large reversible magnetization reaching about 60%. From these results, it is evident that exchange coupling between the soft and hard phases was obtained in this study. (C) 2001 Elsevier Science B.V. All rights reserved.