Mossbauer line tracking study of alpha-transition in FeS.

P. MENDOZA ZÉLIS; G. A. PASQUEVICH; A. VEIGA; M. B. FERNÁNDEZ VAN RAAP; F. H. SÁNCHEZ

La Plata

Conferencia; XI Latin American Conference on the Applications of the Mössbauer Effect; 2008

The structural transition on slightly non stoichiometric FeS is studied by Mössbauer Spectroscopy and Mössbauer Line Tracking methodology. Recent results from different authors lead to uncertainties about FeS transitions that appear in phase diagram handbooks. According to the most recent reports the superstructure derived form the NiAs-type structure transforms into the MnP orthorhombic one near 400K. Both phases coexist within a temperature interval which, depending on sulphur concentration, goes from a few degrees to around 200 K. They are antiferromagnetic with iron atoms located at unique crystallographic sites. The environment of the probes are dierent enough as to allow hyperne elds from both phases to be distinguished. For a Mössbauer Line Tracking experiment a conventional pulse height selection branch, and a Mössbauer driving system in which a novel programmable constant-velocity scaler replaces the usual multiscaler, are used. This set up allows the independent measurement of any channel of a Mössbauer spectrum during an arbitrary period of time. Then, the acquisition of a spectrum region does not necessarily include its central part. Here, this methodology is used to perform a quasi-continuous temperature study of the transition. One or more absorption lines, from both phases, can be followed simultaneously while temperature is varied within the coexistence region. This work is also used as an appropriate test for this novel technique. Therefore, not only the physics of the transition is treated in this contribution, but a description of the technique and a discussion of the applied line tracking algorithm are also presented.