Mössbauer effect in natural strunzite, ferristrunzite and ferrostrunzite

Abstract

The temperature dependence of the ferric and ferrous hyperfine fields in natural samples of strunzite, ferristrunzite and ferrostrunzite is determined by Mossbauer spectroscopy between 4.2 K and their magnetic transition temperatures (T N), i.e. 50.5±0.5 K, 43.0±0.5 K and 44.0±0.5 K respectively, which are determined by Mossbauer thermoscanning. Two dominating magnetically split ferric subspectra were consistently present in all of the samples and are related to the Fe(1) and Fe(2) sites in the crystallographic structure, but an unambiguously assignment to a specific site is not possible. The difference between the corresponding hyperfine fields is very small. In the strunzite sample these fields are well defined and rather weakly dependent of temperature. In the other samples the corresponding hyperfine fields are more distributed especially at higher temperatures (below T N). The relative contribution in the spectra of the third magnetic ferric component differs strongly between the samples and is assigned to ferric ions at the Mn site. At the lowest temperatures applied, its hyperfine field exceeds all other field values, but it decreases rather rapidly with increasing temperature, in so far that the corresponding spectral lines make a crossover with the lines of the other ferric subspectra. The magnetically split spectra of ferrostrunzite consist additionally of a ferrous magnetic component, which could be successfully analysed by introducing two magnetically split ferrous subspectra, which strongly overlap with each other but also with the ferric components. At higher temperatures in the magnetic region all subspectra overlap more and in the case of ferri- and ferrostrunzite the ferric hyperfine fields were distributed over a wider range.