[sdpd] FullProf help with magnetic phase

[Richard Kodama <rkodama...@uic.edu>]

Hello Folks,
   I've been having trouble fitting neutron powder diffraction patterns of 
NiO, a relatively simple antiferromagnet, using FullProf.  Basically, the 
nuclear part of the fit is no problem, but I have trouble with the magnetic 
part.  I've tried a number of methods, but I'll describe what seems to be 
the most straightforward one.  I define a purely magnetic phase, using 
JBT=5.  I define no propagation vectors, and a doubled unit cell.  I 
specify P1 space group and no symmetry elements (the structural space group 
is F m -3 m or R -3 m, depending on whether you consider a slight trigonal 
distortion).  I define positions of ALL magnetic ions in the doubled cell 
(32 Ni2+ ions), with occupancy 1.0.  For each ion, I specify a phase of 0.0 
or 0.5, depending on which sublattice the moment is on.  When I run 
FullProf, after convergence is reached, I get a warning dialog saying 
"Sum(Iobs=0): have you really reflections?".  Then the displayed pattern 
doesn't seem to have any magnetic peaks.
   Can anyone help me out?  Is there an example of a similar approach to 
defining a magnetic phase that someone can point me to?

Thanks,
Richard

______________________________________
Richard Kodama, Assistant Professor
University of Illinois at Chicago
Department of Physics, M/C 273
845 W. Taylor St.
Chicago, IL  60607-7059
voice: 312-996-5358, fax: 312-996-9016
email: rkodama...@uic.edu


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