From: ifeffit-bounces@millenia.cars.aps.anl.gov [ifeffit-bounces@millenia.cars.aps.anl.gov] on behalf of NIRAWAT THAMMAJAK [n.thammajak@gmail.com]
Sent: Friday, May 11, 2012 12:26 PM
To: XAFS Analysis using Ifeffit
Subject: [Ifeffit] Debye function model, Math expression

Hello,

May I add more questions to this. I do a research on magnetic materials. Bond lenghts and geometries are really important to understand the magnetic interactions and I think EXAFS is the promising tool for this. I have measured the EXAFS spectra for quite a complex material system. There are 3 sites of absorbing atom (Fe) in the crystal structure, therefore I created 3 FEFF models to fit the data with different amplitudes. Closest neighbours are oxygen atoms, and then Li. The strongest scatterers are La atoms sitting ~4.26 angtrom away from the absorbing atom, which contribute a significant 3rd shell. Yes, there are many paths to include. Math expressions together with bulk structure details obtained from neutron diffraction help to minimise the parameters somewhat. However, there are thermal factorss, very small but too many of them.

I measured my sample at 1.5 K, then sigma^2 are quite small. Could you please suggest any papers, models, or math expressions constraining these factors at low temperature. Would it be sensible to constrain them as 0, or a range of small numbers obtained from the significant shells?

Thank you very much,
Nirawat.