Improvement of Magnetic Properties of Sm₂Fe₁₇Nx Powder Prepared by MG

Abstract

The preparation of Sm₂Fe₁₇N_x permanent magnet powders was tried by mechanical grinding (MG) and the subsequent nitriding without crystallization heat treatment which was usually needed to obtain Th₂Zn₁₇ structure in the conventional method by MG or mechanical alloying (MA). MG was carried out in NH₃ gas with a rotary ball mill. The powder after MG for 324ks (90hr) had the sufficient nitrogen content of about 35000ppm. The magnetic properties of this powder, however, was insufficient because of the influence of distortion introduced during MG. In order to decrease the distortion, powders were prepared by MG for short time of 18ks-72ks (5hr-20hr). Although these powders contained an insufficient nitrogen of around 10000ppm, nitriding at 723K for 21.6ks in N₂ raised nitrogen content up to 35000ppm. The powder after MG for 18ks and the subsequent nitriding showed the good rectangularity in the demagnetization curve. From this curve, the saturation magnetization and the remanence were confirmed to be about 1.23Wb⋅m_-2 and 1.06Wb⋅m_-2, respectively.