Mössbauer study of amorphous FeF3

Abstract

An amorphous sample of Fe${\mathrm{F}}_{3}$ (enriched in $^{57}\mathrm{Fe}$) has been prepared by vapor deposition at liquid-nitrogen temperature, and its 4.2-K M\"ossbauer Zeeman spectrum is reported. The spectrum consists of six well-resolved broad experimental lines, which indicates the existence of a distribution of electric field gradients, hyperfine fields, and isomer shifts at the iron sites. A quantitative analysis of mean line positions, root-mean-square widths, and line shapes of the six M\"ossbauer lines enables us to obtain new information concerning the statistical distribution of iron environments in the glassy matrix. The electric-field-gradient distribution at the iron sites is composed of equal proportions with positive and negative principal values. The distribution of Zeeman quadrupole-shift energies is very closely of symmetric Gaussian form. The hyperfine-field distribution $p(H)$ possesses a small-amplitude low-field "tail" which at 4.2 K contains (5\ifmmode\pm\else\textpm\fi{}2)% of the total sites. A theoretical explanation of the origin and shape of the tail is given, and it is expected to disappear completely in the limit $T\ensuremath{\rightarrow}0$. The limiting shape of $p(H)$ as $T\ensuremath{\rightarrow}0$ is quantitatively established and is significantly asymmetric about its peak. Numerical values are given for the separate root-mean-square widths of isomer shift, quadrupole shift, and hyperfine-field distributions and for correlations between these variables.