The effect of particle size and consolidating pressure on the magnetic properties of Sm(Co, Fe, Cu, Zr)z bonded magnets

The effect of particle size on the B-r, BHmax and specific density of Sm(Co0.62Fe0.29Cu0.07Zr0.02)(8.0) and Sm(Co0.70Fe0.21Cu0.07Zr0.02)(8.0) bonded magnets has been systematically investigated. It was found that magnets made of powders with a top size less than 53 mu m have a low specific density and, hence, low B-r and BHmax values. Magnets made of powders of about 250 mu m top size, with a composition of Sm(Co0.62Fe0.29Cu0.07Zr0.02)(8.0), yield a specific density of 7.0 gm/cc (84% of theoretical density), a B-r of more than 8.1 kG, and a BHmax of about 15 MGOe, A slight decrease in B-r and BHmax was noticed when the particle top size was increased beyond 710 mu m. This decrease in B-r and BHmax may be attributed to the imperfect grain alignment arising from the fact that each particle may consist of multigrain grains with a random orientation. Because of the slightly lower Fe content, magnets with a composition of Sm(Co0.70Fe0.21Cu0.07Zr0.02)(8.0) exhibit slightly lower B-r and BHmax values when compared to those of Sm(Co0.62Fe0.29Cu0.07Zr0.02)(8.0). However, the relationships of B-r and BHmax to particle size are nearly identical for both compositions. When the powder top size was fixed at about 250 mu m, a consolidating pressure of 8 T/cm(2) appears to be sufficient to obtain magnets with a specific density of 6.9 gm/cc and with a reasonable grain alignment. For Sm(Co0.62Fe0.29Cu0.07Zr0.02)(8.0) bonded magnets, a B-r of 8.5 kG, H-c of 8.5 kOe, H-ci of 23.0 kOe, BHmax of 16.7 MGOe, and H-k Of 8.0 kOe were obtained. (C) 1998 American Institute of Physics. [S0021-8979(98)22411-X].