Structure and magnetic properties of mechanically-alloyed SmZr(CoFe) nanophase hard magnets

Summary form only given. In the recent search for new high temperature permanent magnetic materials, research has concentrated on bulk Sm/sub 2/Co/sub 17/ type magnets. The usual approach to development of coercivity in these bulk materials is to prepare a nanophase cellular microstructure with cell walls which act as pinning sites. In this work, a systematic investigation of structural and magnetic properties is carried out on Sm/sub x/Zr/sub y/(Co/sub 1-z/Fe/sub z/)/sub 100-x-y/ nanocrystalline powders, where 13 /spl les/ x /spl les/ 15, 0 /spl les/ y /spl les/ 5, and 0 /spl les/ z /spl les/ 0.5. The samples were prepared by mechanical alloying followed by an optimized annealing procedure. X-ray diffraction patterns showed that the as-milled powders were amorphous. Substitution of Fe leads to small amounts of /spl alpha/-Fe crystallites in a few compositions. Initially, powders with y = 0 were prepared with a view to optimize the Fe content to yield the best room temperature coercivity and remanence. It was found that z = 0.1 was the best Fe content for all Sm compositions. Samples without Zr showed a mixture of Th/sub 2/Ni/sub 17/ and Th/sub 2/Zn/sub 17/-type structures and room temperature coercivity of 1.4 T. All other compositions were then prepared by varying x and y and keeping z = 0.1. These samples also showed a mixture of Sm/sub 2/Co/sub 17/ phases along with minor amounts of SmCo/sub 5/, dependent on Zr content. Maximum coercivity of 1.7 T at room temperature is obtained in the composition Sm/sub 14/Zr/sub 3/(Co/sub 09/Fe/sub 01/)/sub 83/. Enhanced remanence (/spl sigma//sub r///spl sigma//sub s/ /spl ges/ 0.65) is achieved in all compositions, indicating the intergrain exchange coupling among the fine grains. Initial magnetization curves show that the magnetization behavior in these materials is pinning controlled. A discussion of the variation of magnetic properties with alloying addition and selection of suitable alloys for further studies at high te- perature are presented.