INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
Mössbauer Effect Scanning Experiments
G.A. PASQUEVICH; P. MENDOZA ZÉLIS; A. VEIGA; N. MARTÍNEZ; M.B. FERNÁNDEZ VAN RAAP; F.H. SÁNCHEZ
Conferencia; XII Latin American Conference on teh applications of the Mössbauer Effect; 2010
Universidad Nacional Mayor de San Marcos
The recording of the Mössbauer effect as a function of γ-ray Doppler energy (γΕ) and ofan external parameter (EP), such as temperature, pressure, solid state reaction time, magneticfield, etc., can be regarded as the observation of a γ-ray absorption surface as a function ofγΕ and ΕP. Simple representations of this statement are the γΕ temperature and γΕ magneticfield absorption surfaces shown below. The question which emerges from this consideration is: What is the most convenientway of moving about in this γΕ−ΕP space when performing an experiment with a givenobjective? In this talk we will present and discuss several experimental ideas that we have beendeveloping during the last 10 years in response to this question. Some experiments are scans atselected fixed values of γΕ: for example the study of the hyperfine field temperature dependencein the antiferromagnet FeSn2 and in the ferromagnet Fe3Si, the thermal evolution ofFe73.5Si13.5Nb3Cu1B9 from amorphous to nanocrystalline (Finemet) ribbons, and the magneticresponse of α-Fe, Fe90Zr3B7 nanocrystalline (Nanoperm) ribbons, and Al/Metglass/Al trilayersunder oscillating magnetic fields. In other experiments γΕ was varied following a preconceivedstrategy. In some cases spectral regions, where the manifestation of a minority component phasewas expected, where recorded during longer times, allowing their observation andquantification. In other cases a temperature dependent region of interest (ROI) was establishedon the basis of previous experiments. In this way absorption line tracking experiments havebeen performed in FeSn2 and magnetic transitions have been observed in Fe1-xS and[Fe(Htrz)2(trz)](BF4) (Triazol). Recently a new approach involving magnetic fields wasinitiated, which we have named Mösbauer susceptibility, which will be the subject of acontributed talk. The analysis of most of these experiments is performed using Mössbauer effect knownexpressions. However, special care has to be taken in considering absorber thickness effects inorder to produce quantitative precise evaluations of the results. Moreover, and especially whenmaterials magnetic responses are studied, saturation polarization combined effects must betaken into account. When this is done, new physics emerges and allows for example theexperimental determination of the mean values of the square of the three cosine directors of themagnetic moments corresponding to a given Fe site. This differs from what happens whenmeasuring thin absorbers, in which case just one cosine director mean square value can beobtained. The theoretical analysis has been confirmed performing field dependent experimentson thick and thin α-Fe absorbers. The experimental approach subject of this talk has lead to the development of somepieces of hardware and software. The hardware includes from constant velocity signalgenerators with optimized waveforms, to new versatile programmable multiscalers.