I am refining the magnetic structures and moments on NdMnAsO powder. I met a weird situation:
Based on the symmetry analysis, Nd and Mn have the overlapped symmetry Gama10 (AFM arrangement in ab plane for Nd or Mn). I tried two methods to test such magnetic structures at 2K.
1). I produced a new PCR using the same Gama10 for both magnetic Nd and Mn atoms and copy it in the main PCR. There are two phases in the updated PCR; structure, magnetic structures of both Nd and Mn. I obtained very good refinement with the magnetic moments of Nd and Mn along a axis.
2). I produced two individual PCRs for Mn and Nd atoms using the same symmetry Gama10 and copied them in the main PCR. In this case, I have three phases: structure, Nd magnetic structure and Mn magnetic structure. However, I cannot refine it well even I use the same magnetic moments of Nd and Mn that I obtained from the above method.
Why does this happen? In my understanding, these two methods should yield the same results. Is there something wrong with the 2nd method? Does that mean I cannot use individual PCR for each magnetic atom and I must I use one PCR for all the magnetic atoms?
I also want to try using Gama10 (AFM in ab plane for Mn) and Gama3 (FM along c for Nd) to create two individual PCRs to check this magnetic structure. If I must use one PCR for these two magnetic atoms, how can I refine such magnetic structure using the different symmetries?
I appreciate your help in advance!
I suspect that this is a bug which is probably there in the FullProf program. Please contact my colleague Juan Rodriguez-Carvajal of Institut Laue-Langevin and ask him for advice. Again this may be due to complexity of the magnetic structure in NdFeAsO which is nor really properly solved. The reported single crystal neutron diffraction results are not consistent with those of neutron powder diffraction.
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