SPIN-FLIP AND TROILITE-MNP STRUCTURE TRANSITION IN FES AS STUDIED BY MOSSBAUER-SPECTROSCOPY

Synthetic FeS (troilite) was analyzed by Mossbauer spectroscopy in the temperature range 283 less-than-or-equal-to T less-than-or-equal-to 460 K. Spectra were analyzed applying the full Hamiltonian. The alpha transition between the troilite and MnP-type structures was completed at 413 K on heating. Compared with literature data of a meteoritic troilite, the behavior differed as follows: the transition occurred without hysteresis, with a steeper slope in an MnP structure concentration ([MnP]) vs temperature plot, with a lower [MnP] at room temperature, and with heating and cooling trends coinciding. The spin flip in the MnP structure occurred rapidly and is suggested to be coupled to the ease of the alpha transition. The absence of trace elements, e.g. Cr, in the synthetic sample is suggested to be of importance to the rapid spin flip and alpha transition. A reported increase in compressibility of troilite with increased pressure is suggested to be due to a successive weakening of the Fe3 cluster bond strength. The relatively scarce occurrence of electron transfer enzymes with reaction centres with three Fe atoms is suggested to be due to an evolutionary drawback caused by the possibility of forming energetically stable Fe3 clusters unsuitable for reaction.