IFLP   13074
Unidad Ejecutora - UE
congresos y reuniones científicas
Mössbauer Effect Scanning Experiments
Conferencia; XVII ava Latin American Conference on the application of the Mossbauer Effect; 2010
Institución organizadora:
San Marcos University
Mössbauer Effect Scanning Experiments G.A. Pasquevich, P. Mendoza Zélis, A. Veiga, N. Martínez, M.B. Fernández van Raap and F.H. Sánchez1 La Plata Institute of Physics and Physics Department, Facultad de Ciencias Exactas, Universidad Nacional de La Plata. C.C. 67, (1900) La Plata, Argentina The recording of the Mössbauer effect as a function of -ray Doppler energy () and of an external parameter (P), such as temperature, pressure, solid state reaction time, magnetic field, etc., can be regarded as the observation of a -ray absorption surface as a function of andP. Simple representations of this statement are the Doppler velocity – temperature and Doppler velocity – magnetic field absorption surfaces shown below. The question which emerges from this consideration is: What is the most convenient way of moving about in this P space when performing an experiment with a given objective? In this talk we will present and discuss several experimental ideas that we have been developing during the last 10 years in response to this question. Some experiments are scans at selected fixed values of : for example the study of the hyperfine field temperature dependence in the antiferromagnet FeSn2 and in the ferromagnet Fe3Si, the thermal evolution of Fe73.5Si13.5Nb3Cu1B9 from amorphous to nanocrystalline (Finemet) ribbons, and the magnetic response of -Fe, Fe90Zr3B7 nanocrystalline (Nanoperm) ribbons, and Al/Metglass/Al trilayers under oscillating magnetic fields. In other experiments was varied following a preconceived strategy. In some cases spectral regions where the manifestation of a minority component phase was expected, where recorded during longer times, allowing their observation and quantification. In other cases a temperature dependent region of interest (ROI) was established on the basis of previous experiments. In this way absorption line tracking experiments have been 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 was initiated, which we have named “Mösbauer susceptibility”, but this will be the subject of a contributed talk. The analysis of most of these experiments is performed using Mössbauer effect known expressions. However special care has to be taken in considering absorber thickness effects in order to produce quantitative precise evaluations of the results. Moreover, and especially when materials magnetic responses are studied, saturation – polarization combined effects must be taken into account. When this is done, new physics emerges and allows for example the experimental determination of the mean values of the square of the three cosine directors of the magnetic moments corresponding to a given Fe site. This differs from what happens when measuring thin absorbers, in which case just one cosine director mean square value can be obtained. The theoretical analysis has been confirmed performing field dependent experiments on thick and thin -Fe absorbers. The experimental approach subject of this talk has lead to the development of some pieces of hardware and software. The hardware includes from constant velocity signal generators with optimized waveforms, to new versatile programmable multiscalers. 1sanchez@fisica.unlp.edu.ar