Preparation of Sm2Fe17Nx anisotropic powder by mechanical grinding in NH3 atmosphere

Sm2Fe17Nx, powders with magnetic anisotropy have been prepared by mechanical grinding (MG) in NH3 atmosphere using a rotary ball mill. The hydrogen content of Sm2Fe17Nx powders after MG increased rapidly till 72 Its with increasing MG time, and showed the maximum at 72 ks. Beyond 72 ks, it decreased with increasing MG time. On the other hand, the nitrogen content monotonously increased with MG time, and it was kept constant beyond 432 ks. Though the powder after MG for 288 ks absorbed 35000 ppm of nitrogen, the magnetic properties of this powder were deteriorated due to the distortion which was introduced into the powder during MG. The powders were prepared by MG for shorter periods between 18 similar to 144 ks and subsequent nitriding. Their magnetic properties such as remanence and rectangularity of the demagnetization curve were extremely improved. The remanence over 1.0 Wb.m(-2) and the maximum energy product of 129 kJ.m(-3) (16.1 MGOe) were obtained for the powders prepared by MG for 18 and 36 ks and subsequent nitriding. X-ray diffraction patterns of the powders aligned in the magnetic field showed the growth of the (006) peak. This indicates that these powders have the magnetic anisotropy. It is considered that an increase of MG time deteriorates the magnetic anisotropy due to the pulverization of powders.