A Mössbauer study on the surface hyperfine field of uniform hematite particles

Abstract

A Mössbauer spectroscopic study was performed on uniform spherical hematite particles (99±9 nm, Sample I) and those enriched with⁵⁷Fe on the surface (Sample II). A striking difference was found between the spectra of these two samples, in that Sample I showed a spectrum with nearly symmetrical resonant absorption lines, while Sample II showed a spectrum with the lines broadened toward the central peaks asymmetrically. But after the⁵⁷Fe-enriched sample was heated to 623 K, the spectral lines became narrower due to the diffusion of the surface⁵⁷Fe-ions into the bulk. The above results showed that the centripetal broadening of the spectral lines for small uniform hematite particles resulted from a surface effect. The surface exhibited a hyperfine field about 5.2% lower than that for the bulk. The wider distribution of the surface hyperfine field was explained by structural inhomogeneity of the surface.