I have been struggling with a similar problem recently. I can't seem to
create non-zero magnetic moments for my magnetic phase is GSAS.
Presumably this is because I've input my magnetic symmetry information
incorrectly and they are disallowed or constrained to zero.
Assuming the GSAS spin colors black and red correspond to white and
black respectively, I'm still having trouble relating the colored
Shubnikov groups to the GSAS input menus.
This is from the 'Edit magnetic moment' menu:
All of the following data refer to the current space group symbol
The unique symmetry operations and the associated spin colors are
Mx M110
Black Black
The current d-star limit for magnetic reflections is 1.00
No magnetic atoms were found
What is meant by 'unique symmetry operations', and what is the notation
'Mx' and 'M110'? How is this related to those symmetry operations in an
uncolored space group that are combined with the anti-symmetry (i.e.
time-reversal, spin-flip) operation? How are grey groups handled?
The following menu is now available for editing the magnetic moments:
The magnetism editing options are
A - List all of the atoms
C - Change the d* limit for single crystal magnetic reflections
L - List the current settings
M n - Modify the moment on atom sequence number "n"
S - Modify the spin flip model
X - Return to atom editing
Enter magnetism editing option (<?>,A,C,L,M,S,X) >
If I try to create a moment on atom #1 with 'm 1' at the prompt, I get:
Enter magnetism editing option (<?>,A,C,L,M,S,X) >m 1
0.000000 0.000000 0.000000
No magnetic moment is currently defined
Constraints on the moment are 0 0.00 0 0.00 0 0.00
New moment = 0.00000 0.00000 0.00000 0.000 0.000 0.000
Enter magnetism editing option (<?>,A,C,L,M,S,X) >
...and I'm back at the same prompt, with no chance to enter a moment.
As a test, I tried the above sequence with each of the possible
permutations of the spin-flip colors:
Mx M110
Black Black
Mx M110
Black Red
Mx M110
Red Black
Mx M110
Red Red
All of these give the same results, i.e. I cannot enter a magnetic
moment.
Hopefully I'm just missing something obvious. If someone could point me
at a reference or a worked example I would be grateful.
Thanks,
-- John Henry
John Henry J. Scott
NIST Microanalysis Research Group
http://www-sims.nist.gov/Division/Contacts.html