Role of Washing Solvents in Defining the Magnetic Performance of Sm2Fe17N3 Obtained by Reduction Diffusion

Calciothermic reduction-diffusion (RD) is one of the leading synthesis methods for Sm2Fe17N3 (SmFeN), but sintering of such RD-derived powders is hampered by oxidation and CaO byproducts. Here, we systematically evaluate how post-synthesis washing solvents govern powder chemistry and magnetic performance. RD-synthesized SmFeN powder was washed with several aqueous and non-aqueous solvents using identical washing protocols. This was followed by an assessment of both the as-washed powder as well as after annealing at 425 degrees C. Phase content was quantified by synchrotron PXRD and Rietveld refinement and SEM/EDS. The oxygen content of the powders was determined via inert gas fusion and the magnetization by DC magnetometry. While all aqueous-based solutions were able to remove CaO, the non-aqueous solutions were only effective with extended washing times. Prior to annealing, the crystalline phases and magnetic properties of the as-washed powders were largely the same regardless of washing solvent. However, differences emerge after annealing, where water-based washing markedly lowers the coercivity (H-c similar to 3.8-4.3 kOe). In contrast, non-aqueous NH4Cl-methanol washing protocols were more effective in preserving coercivity (H-c similar to 4.9-5.9 kOe). We attribute this to lower oxygen content in the non-aqueous samples (similar to 9400 ppm v similar to 6400 ppm, respectively) which in turn reduced the formation of alpha-Fe during annealing. These results highlight the importance of solvent choice in washing RD-synthesized SmFeN and demonstrate that non-aqueous protocols, which better limit oxidation, outperform aqueous solvents despite the need for longer washing times.