Nanocrystallite Fe-O alloys investigated by Moessbauer- and x-ray diffraction

Full text: Ternary skutterudites RExTM4X12 are of large interest because of their high thermoelectric potential. To get more information about magnetic ground state we have investigated samples with RE = Yb, Nd, Pr and TM = Fe by magnetic and high field Moessbauer investigations. From x-ray investigation the Fe and Sb sublattice is found to be fully occupied, whereas a considerable amount of voids is present in the RE - sublattice (e.g. for Pr x = 0.73). Theoretical investigations predict zero moment at the Fe-site. In contrast to this magnetic measurements point to a considerable large Fe-moment. Although there exist only one crystallographic site for Fe, from analysis of the 57Fe x-ray and Moessbauer investigations were carried out on powders produced by milling of Fe2O3 + α-Fe mixtures in a high energy ball mill and subsequent low-temperature annealing. The nanocrystalline composite alloys obtained after milling, contained FeO and α-Fe with an average crystallite size of 15-20 nm as well as an amorphous phase. Alloys subjected subsequent annealing contained, however, only α-Fe + Fe3O4 with an average crystallite size of about 20 nm. Unlike the starting materials the produced powders had properties, which were characteristic for hard magnetic materials. (author)