Thickness and polarization effects in magnetic Mössbauer scans

P. MENDOZA ZÉLIS; PASQUEVICH G.A; L. LENCINA

La Plata, Argentina

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

Over the last years, the Mossbauer Scan, that is the Mossbauer transmission recorded at xed photon energies as a function of a given physical parameter such as temperature, external eld, etc., is being developed as a useful quantitative tool, complementary to Mossbauer spectroscopy [1,2]. Magnetic Mossbauer Scans (MMS) [2], in particular, seem to be promising because they are of easy implementation, and additional information can be obtained. When using this technique, the Mossbauer transmission is recorded while the sample is subject to an ac magnetic eld. For a pure magnetic hyperne splitting, the Mossbauer absorption lines intensity depends on the sample magnetic moments distribution. If a thin absorber is considered, this dependence is only determined by the mean square projection (MSP) of the magnetic moments distribution in the gamma ray direction. For thicker absorbents, the Mossbauer pattern also depends on the asymmetry of the MSP over the plane perpendicular to the gamma ray direction. This thickness eect occurs due to the fact that the gamma beam changes its polarization state as it goes through the sample. In fact, this eect appears even if the source is not polarized. Then, a properly chosen set of MMSs allows the determination of the magnetic moments MSP dependence on the magnetic eld applied in a quasi-continuous way.The aim of this work is to deepen our knowledge about this new technique; thus, we simulate the expected MMS patterns for dierent magnetic moments distribution and their dependence according to the applied magnetic eld, by using dierent models and a proper numerical analysis.Finally, we envisage the quantication of the error quantication made in the determination of MSP, when the information about the magnetic moment distribution is obtained from Mossbauer spectra using a thin lm approximation. We perform this numerical study for several sample thicknesses by modelling dierent magnetic moments distributions.[1] P. Mendoza Zelis, G. Pasquevich, F. H. Sanchez, N. Martinez and A. Veiga. "A newapplication of Mossbauer eect thermal scans: determination of the magnetic hyperfineeld temperature dependence", Physics Letter A, 298, (2002) pp 55.[2] A. Veiga, N. Martinez, P. Mendoza Zelis, G.A. Pasquevich, F.H. Sanchez, "Advancesin constant-velocity Mossbauer instrumentation", Hyperfine Interact. 167 (2006), pp 905.