Magnetic properties and structure of bulk nanocrystalline Sm(CoCuFeZr)7.6 sintered magnet

Abstract

Structure and magnetic properties were studied for Sm͑Co 0.74 Cu 0.12 Fe 0.1 Zr 0.04 ͒ 7.6 nanocrystalline ball milled powders and bulk magnet consolidated via spark plasma sintering technique. The amorphous milling powders crystallize to TbCu 7 structure or a mixture of Th 2 Zn 17 and CaCu 5 structures when annealed below or above 1023 K, respectively. The coercivity of the powders decreases from 1.27 to 0.56 T as the annealed temperature increases from 923 to 1223 K. The bulk magnet also exhibits a TbCu 7 structure with an average grain size of 32 nm. Magnetic measurements show that the remanence is 0.49 T and the coercivity reaches as high as 1.42 T. The Mr/Ms ratio of 0.63 demonstrates the existence of intergrain exchange coupling among the nanograins. The magnet exhibits the coercivity of 0.27 T at 773 K.

Thermodynamic and experimental study on phase stability in nanocrystalline alloys

“…a hexagonal Th 2 Ni 17 -type crystal structure (b-Sm 2 Co 17 ) exists stably at room temperature instead of a rhombohedral Th 2 Zn 17 -type crystal structure (a-Sm 2 Co 17 ), which is well known as the stable room-temperature phase in the conventional polycrystalline Sm 2 Co 17 alloys. Since the nanostructured single-phase Sm 2 Co 17 is the basis for the nanocrystalline Sm 2 Co 17 -type magnets of various compositions [26,27], the understanding of phase transformation characteristics in nanocrystalline Sm 2 Co 17 alloy will facilitate the development of nanocrystalline Sm 2 Co 17 -type alloys with superior magnetic properties for applications at room temperature and high temperatures.…”