Magnetic Properties of Sm_2Fe_(17)N_x Powders Prepared by Mechanical Grinding

摘要

Using Sm_(2.5)Fe_(17) alloy powder of - 100 mesh, the preparation of Sm_2Fe_(17)N_x magnetic powder whose grain size is finer than the single magnetic domain size was carried out by mechanical grinding (MG) and subsequent heat treatments for crystallization, nitriding and annealing. The effects of MG time and heat treatment on the factors such as the grain size, nitrogen and oxygen content, the precipitation of a-Fe and magnetic properties have been investigated. The results obtained are summarized as follows:(1) The grain size of powders after MG was about 10-30 nm and it was extremely finer in comparison with the single magnetic domain size of about 300 nm. Although the grain size was coarsened by the subsequent heat treatments, it was about 50 nm even after annealing.(2) The precipitation of #alpha#-Fe was caused by the oxidation of powder, and it was confirmed that the oxygen content of the powder should be lower than 9000 ppm in order to prevent the #alpha#-Fe precipitation.(3) The maximum coercivity of 2.24 MA centre dot m~(-1) was obtained under the following condition; i.e., MG time: 108 ks, crystallization: at 1023 K for 1.8 ks, nitriding: at 723 K for 129.6 ks and annealing: at 623 K for 7.2 ks in N_2.