Structure and hyperfine properties ofSm2(Fe,Si)17

Abstract

Nanocrystalline iron-rich intermetallic compounds ${\mathrm{Sm}}_{2}{\mathrm{Fe}}_{17\ensuremath{-}x}{\mathrm{Si}}_{x}$ $(x=0,$ 0.5, 1, 1.5, and 2) were studied by means of x-ray diffraction and M\ossbauer spectroscopy coupled with Curie temperature and magnetization measurements. The mechanically alloyed and annealed compounds are single-phase with the rhombohedral ${\mathrm{Th}}_{2}{\mathrm{Zn}}_{17}$-type structure. The Curie temperature is found to increase with Si content x, whereas the unit-cell parameters, calibrated against Bragg reflections of a standard Si powder that was mixed with our samples, are found to decrease. The magnetic moment per Fe atom, deduced from magnetization measurements at 4.2 K up to 90 kOe, increases with x. The best Rietveld agreement factor favors a preferential occupation of Si on the $18h$ site. These results are corroborated by the M\ossbauer spectroscopy measurements obtained from 295 K down to 77 K. The M\ossbauer spectra analysis is based on the correlation between the Wigner-Seitz volume and the isomer-shift evolution of each specific site $6c,$ $9d,$ $18f,$ and $18h$ of the $R3\ifmmode\bar\else\textasciimacron\fi{}m$ structure. For all Si concentrations the magnitude of the hyperfine fields is ${H}_{\mathrm{hf}}(6c)g{H}_{\mathrm{hf}}(9d)g{H}_{\mathrm{hf}}(18f)g{H}_{\mathrm{hf}}(18h).$ The mean hyperfine field decreases with x content.