Neutron Magnetic Refinement in TOPAS 7 using ions not in magdata.dat

nathan_d_arndt

Hello,

I am trying to refine the magnetic contribution to the scattering of a CW neutron scattering data, unfortunately two of the magnetic ions that are in my structure are not included in the magnetic form factor file (magdata.dat).

I have been able to find the magnetic form factors at an ILL page. I believe I should be able to just add the lines that are need into magdata.dat, but as this is my first time using TOPAS I wanted to ask here if there is a way to do this that does not involve changes to the files within the TOPAS directory.

Any help, tricks, or confirmation would be appreciated. If this is the path to fixing this issue I will of course be making a back up of the original magdata.dat file.

Thank you in advance!

johnsoevans

That should be all you need to do.
Just be careful that the coefficients you use correspond to the equations used in TOPAS. They are stated at the top of magdata.dat. Note in particular that you need to retain the two 0.000 values in the table. There are some parameterisations around that use more terms that the A,a,B,b,C,c,D formalism in topas (e.g. Kobayashi uses 10 terms for <j0>) . You can't just type the extra values into the columns with zeros. Apologies if this is patronising, but others have done this!
You can leave regular TOPAS notes in magdata.dat to record changes you make.

nathan_d_arndt

Thank you for the quick response! No apologies needed, I feel much more comfortable editing the file now.