Hi Andrew,
A word on GSAS vs Fullprof:
GSAS can only handle a magnetic structure that can be defined by a unit
cell. So, your incommensurate structure would need to be close to a
lock-in value to work, i.e. (0 0 0.32) is close to (0 0
1/3).
While it is a lot easier to use a super cell, the peak positions don't
line up. In this gratuitous self citation:
"High-resolution powder neutron diffraction study of helimagnetic order
in CrP1-xVxO4 solid solutions"
J. P. Wright, J. P. Attfield, W. I. F. David, and J. B. Forsyth
Phys. Rev. B 62, 992 (2000)
... there is an example of a (~1/3,0,0) that didn't lock in. The
conclusion was that the student could not avoid learning to use a
program that has propagation vectors ;-)
Cheers,
Jon
