Potentiodynamic polarization measurements for Sm2Fe17N3 magnetic powders in organic solvents with H3PO4 were performed to determine which additives promote passivation in the ball-milling process and improve the coercivity of the ball-milled powders at high temperatures. Surface films that contained FePO4 formed on the Sm2Fe17N3 powders in the solvents with H3PO4 and inhibited the dissolution reaction during anodic polarization. It would appear that the FePO4-containing surface film acts as a barrier against oxidation at high temperatures. It was demonstrated that the addition of either PO(OCH3)(3) or HNO3 to an isopropyl alcohol solution in the ball-milling process suppressed the decrease in coercivity above 500 K. (C) 2016 Elsevier Ltd. All rights reserved.