Dear Ross, Thanks for your reply. Sorry for being so exclusive in my initail mail, of course I should have included everyone! The title of PhD student also applies to me.
I've seen a talk about SARAh by Andrew Wills at ISIS and was impressed by it. Therefore I've already downloaded it but didn't succeed in using it yet. The problem is actually already at the beginning: In my GSAS file I created a second phase with P1 and just copied the atoms of the main phase over. I loaded that file by clicking <GSAS Controls>, <Load GSAS EXP file> How do I then define the MAT file? Sorry, it must be obvious but I can't find it. I am happy to read some documentation but couldn't find any on the website ( http://www.chem.ucl.ac.uk/people/wills/index.html). Thanks again for your help Alex 2009/7/23 Ross H Colman <ucca...@ucl.ac.uk> > Dear Alex, > > You addressed your email to "experts on magnetic refinement" so I > apologise if I am the only person to reply for I am a lowly PhD student. > > I am afraid I am not going to answer your questions directly but instead > point you to the program that I use for magnetic refinements. Its free > software available on CCP14 called SARAh. It allows you to input your > magnetic atom sites, space group and k-vector then has the ability to > modify your fullprof pcr file depending on how you wish to do the > refinement. > > The process is a little involved, as it uses representational theory to > reduce your problem to symmetry allowed structures, rather than freely > refining all variables, but it has step by step instructions and I think > there are even some online help videos for using it now. > > Available from: > www.CCP14.ac.uk or > www.chem.ucl.ac.uk/people/wills/index.html > > Best regards and good luck > Ross Colman > > > > Dear experts on magnetic refinement, > > > > We recently got some nice data on GEM, ISIS and I was able to get a > decent > > structural fit using GSAS and FullProf. > > > > Now I would like to refine the magnetic structure but this is my first > > time > > so I struggle to give FullProf what it wants. > > > > Since I'm a novice treating the magnetic data I'd have some general > > questions about the input (which I attached below). The general structure > > of > > the pcr file seems to be OK, because it is read by FP but unfortunately > in > > the current form leads to a singular matrix. I'm sure I've done something > > wrong with the input parameters. > > > > Here is a quick outline of what I want to achieve: > > There are two magnetic ions in the structure. Mn and Co, but Co has a > very > > small moment (we know that from neutron diffraction from the 80's). The > > moments seem to order in two incommensurate spiral structures (one for Mn > > and one for Co) with the k-vector along c-axis. I thought it is best to > > include a separate purely magnetic phase in FP. Would you agree and if > yes > > can I still do a multi-bank refinenment? > > > > Here is the snippet from the pcr file which was inspired by Ho2Cu2O5, an > > example from the FP webpage (questions below): > > > ---------------------------------------------------------------------------------------------------------------------------------------------- > > CoMnSi(magnetic > > reflection) > > > > ! > > !Nat Dis Mom Jbt Isy Str Furth ATZ Nvk More > > 2 0 0 -1 -1 0 0 0.0000 2 1 > > !Jvi Jdi Hel Sol Mom Ter > > 3 0 0 0 0 0 > > !Contributions (0/1) of this phase to the 6 patterns (FOR simplicity I > > deleted all but the first pattern to get started) > > 1 > > !Irf Npr Jtyp Nsp_Ref Ph_Shift for Pattern# 1 > > -1 13 -1 0 0 > > ! Pr1 Pr2 Pr3 Brind. Rmua Rmub Rmuc for Pattern# 1 > > 0.000 0.000 1.000 1.000 0.000 0.000 0.000 > > P -1 <--Space group symbol > > !Nsym Cen Laue MagMat > > 4 1 3 1 > > ! > > SYMM x,y,z > > MSYM u,v,w,0.0 > > SYMM -x,-y,z+1/2 > > MSYM u, v,-w,0.0 > > SYMM x+1/2,-y+1/2,z > > MSYM -u,v,-w,0.0 > > SYMM -x+1/2,y+1/2,z+1/2 > > MSYM u,-v,-w,0.0 > > ! > > !Atom Typ Mag Vek X Y Z Biso Occ Rm > > Rphi Rtheta > > ! Im Iphi Itheta beta11 beta22 beta33 MagPh > > Co1 MCO2 1 1 0.15609 0.25000 0.05324 0.00000 1.00000 > > 0.3 23.0 > > 45.0 > > > > 220.00 0.00 230.00 280.00 0.00 0.0 > > 0.0 0.0 > > 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 > > 0.00 0.00 0.00 0.00 0.00 0.00 > > Mn1 MMN2 1 2 0.02093 0.25000 0.68070 0.00000 1.00000 > > 3.1 178.0 > > 13.0 > > > > 0.00 0.00 0.00 0.00 0.00 > > 0.0 0.0 0.0 > > 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 > > 0.00 0.00 0.00 0.00 0.00 0.00 > > !-------> Profile Parameters for Pattern # 1 > > ! Scale Extinc Bov Str1 Str2 Str3 Strain-Model > > 4.8798 0.0000 0.0000 0.0000 0.0000 0.0000 0 > > 1.00000 0.00 0.00 0.00 0.00 0.00 > > ! Sig-2 Sig-1 Sig-0 Xt Yt Z1 > > Z0 Size-Model > > ! 0.000 186.666 0.000 <- Instr. par. + shifts. Only shifts > are > > refined > > 0.000 33.363 0.000 0.000 0.000 0.000 > > 0.000 0 > > 350.00 31.00 0.00 0.00 0.00 0.00 > > 0.00 > > ! Gam-2 Gam-1 Gam-0 LStr LSiz > > ! 0.000 0.000 0.000 <- Instr. par. + shifts. Only shifts are > > refined > > 0.000 0.000 0.000 0.000 0.000 > > 0.00 0.00 0.00 0.00 0.00 > > ! a b c alpha beta gamma > #Cell > > Info > > 5.866537 3.692333 6.856417 90.000000 90.000000 > > 90.000000 > > > > 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 > > ! Pref1 Pref2 alph0 beta0 alph1 Kappa > > ! Instr. par. + shifts: 1.597107 24.016417 1.496805 46.025921 > > <- > > Only shifts are refined > > 1.000000 0.000000 0.000000 -3.937651 0.000000 0.000000 > > 0.00 0.00 0.00 40.00 0.00 0.00 > > !Absorption correction parameters > > 0.00000 0.00 0.00000 0.00 ABS: ABSCOR1 ABSCOR2 > > !Propagation vector 1 > > 0.00000 0.00000 0.2300000 > > 0.00 0.000 1.000 > > !Propagation vector 2 > > 0.00000 0.00000 0.2000000 > > 0.0000 0.0000 1.000 > > > ------------------------------------------------------------------------------------------------------------------------------------------------ > > > > Questions (forgive me if they are obvious but I'm really just starting) > > > > 1) How do I decide on the space group? With incommensurate structures is > > it > > always just P -1 > > > > 2) Cen: IF I choose P -1 as the space group don't I have to set Cen to 2 > > (i.e. centro-symmetric) > > > > 3)Laue: Is that the Laue symm of the the underlying crystallographic > > phase? > > > > 4)SYM and MSYM: Is there a way to create them or do I have to deduce them > > by > > the space group I choose. Because for P -1 I wouldn't expect a +1/2 > > component in them (do they come from the Laue sym?). There is really not > > much about this in the FP manual > > > > 5) Atom types: Where in the manual do I find the correct types I have to > > use? Is it always just M in front of the atom? > > > > 6)Do I enter the propagation vectors just as I did it, or do I have to do > > something different? > > > > > > To whoever takes the time in answering even just a small number of these > > questions or giving any advice I am really thankful. I'm very intrigued > by > > this magnetic neutron scattering business but it's sometimes hard to keep > > on > > top of all the arising issues. > > > > With best regards > > Alex > > > > >
