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
