A 57Fe Mössbauer study of nanostructured Sm2Fe17−xCoxC3

Sm2Fe17−xCoxC3 (x ≤ 2) were synthesized by means of reaction with solid hydrocarbon at 693 K on Sm2Fe17−xCox powders obtained by high energy milling and subsequent annealing at 1125 °C. X-ray diffraction analysis by Rietveld method has shown that both series crystallize in the rhombohedral Th2Zn17-type structure. The Curie temperature TC increase of Sm2Fe17−xCoxC3 versus Co content is only ruled by electronic effect less pronounced than for the non-carbonated series. The analysis of their Mössbauer spectra, have been analyzed on the basis of the binomial law. The hyperfine parameter sets were assigned according to the relationship between the Wigner-Seitz cell volume of each iron site and their isomer shift δ so that δ{6c} > δ{18h} > δ{18f} > δ{9d}. It results that Co preferentially occupies the 18h site with the recurrent sequence HHF{6c} > HHF{9d} > HHF{18f} > HHF{18h}. This sequence is in agreement with the number of iron near-neighbors. The increase with Co content of hyperfine field, is correlated to the increase of the core electron polarization field ruled by the asymmetrical filling of the 3d band by the additional 3d Co electron.