The effects of nitriding on the magnetic properties of Sm–Fe- and Sm–Fe–Ta-based materials

Interstitial Sm–Fe-based nitrides with compositions close to that of Sm2Fe17N3 are an interesting class of hard magnetic materials. In this series of experiments we characterised the nitrogenation process using a vibrating-sample magnetometer (VSM) and a thermogravimetric differential thermal analyser (TG/DTA). The VSM was fitted with a high-temperature furnace tube and a system for varying the atmosphere around the sample with different gases between 10−2 mbar and 1 bar. The experiments involved two alloys, with the compositions Sm13.7Fe86.3 and Sm13.8Fe82.2Ta4.0, and three different particle sizes, <2 mm, <200, and <15 μm. The results show that the nitriding process is very sensitive to the composition and the particle size, and that nitriding at higher temperatures can result in a nitrogen disproportionation and a loss of the Sm2Fe17 phase.