Rare-earth iron-based intermetallic compounds and their carbides: Structure and magnetic behaviors

The structural and magnetic properties of Sm2Fe17-xMoxSm2Fe17-xMox, its out of equilibrium precursor SmFe9-yMoySmFe9-yMoy and their carbides are investigated by means of powder X-ray diffraction, magnetic measurements and high-resolution transmission electron microscopy. The structure of the nanocrystalline Sm1-s(Fe,Mo)5+2sSm1-s(Fe,Mo)5+2s alloys are governed by the s Sm vacancy rate and the x   amount of Mo. In this work, the Rietveld analysis shows that for s=0.33s=0.33 the structure is R3¯m of Th2Zn17Th2Zn17-type and P6/mmmP6/mmm with the stoichiometry 1/91/9 for s=0.36s=0.36. Moreover, it points out a lattice expansion along the c  -axis after Mo substitution for Fe and reveals a 6c6c preferential occupation for Mo atoms in R3¯m structure, and 2e2e for the out of equilibrium hexagonal precursor. Upon carbon insertion, the lattice expansion favors the Curie temperature increase up to 35% for Sm2Fe16.42Mo0.58C2Sm2Fe16.42Mo0.58C2 and 49% for the metastable SmFe8.7Mo0.3CSmFe8.7Mo0.3C carbide. The Curie temperature and the coercive field of the 1/91/9 carbides are higher than those of 2/172/17 ones. This makes the out of equilibrium hexagonal precursor a competitive candidate for use as permanent magnet.