Sm-(Fe, Mn)-N Magnet Powder Made by Reduction and Diffusion Method

Abstract

We have produced Sm₂(Fe, Mn)₁₇N_x coarse powders by a reduction and diffusion (R/D) method and investigated the characteristics. The Sm₂(Fe, Mn)₁₇ mother alloy powder made by the R/D method showed rounded shape and sharp particle size distribution, and was consisting of almost only Th₂Zn₁₇-type phase with minor α-Fe. For the nitrided Sm₂(Fe, Mn)₁₇N₃ compound, the Mn addition increased the lattice constants of the Th₂Zn₁₇ structure and decreased both Curie temperature and magnetization of the compound. The nitrogen content of Sm₂(Fe_,Mn)₁₇N_x coarse powder increased with increasing coercive force and decreasing magnetization. The nitrogenation of x>5 resulted in high corecive force more than 900 kA/m. The highest magnetic properties of Sm₂(Fe_0.95Mn_0.05)₁₇N_x coarse powder is B_r=1.10 T, H_cJ=720 kA/m and (BH)_max=193 kJ/m³ at x=4.2. The Sm₂(Fe_0.95Mn_0.05)₁₇N_x magnet powder indicated good thermal stability. The deterioration of coercive force of Sm₂(Fe_0.95Mn_0.05)₁₇N_4.5 powder after exposure at 160 °C for 160 h was as small as those of MQP-O and Sm₂Co₁₇ powders. The coercive force of an Sm₂(Fe_0.95Mn_0.05)₁₇N_x injection molded magnet with PPS was almost the same as the powder used. The time dependence of irreversible flux loss at 180 °C was similar to that of Sm₂Co₁₇ bonded magnets.