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 >
