High coercivity in Sm2Fe17N<i>x</i> magnets

Using mechanical alloying and a subsequent two-step heat treatment we produced magnetically isotropic microcrystalline Sm2Fe17Nx samples with room-temperature coercivities up to 24 kA/cm (30 kOe). The remanence and the energy product are equivalent to similarly prepared Nd-Fe-B samples, but the properties at elevated temperatures are superior because of the high Curie temperature of 470 °C and the large anisotropy field of 14 T at room temperature. From differential scanning calorimetry it is concluded that the 2:17 nitride is metastable. It decomposes into Sm nitride and α-Fe above 600 °C.