Magnetic Rietveld Refinement

lijia-zhou

Dear all

I follow Magnetic Rietveld Refinement of LaMnO3 example to process my data.
First I used Nuclear + Magnetic Combination
I created a separate magnetic supercell with new a(mag)=a(nuclear), b(mag) = a(nuclear),. c(mag) = 2c(nuclear)
It can be runed, but When I run magnetic data, the following happens：
Error:
Space group P1 is not centrosymmetric
Number of equivalent positions 1
Number of hkls generated for D:\TOPAS-5\sg\pmmm.sg 341
Space group Pmmm is centrosymmetric
Number of equivalent positions 8
Number of hkls generated for D:\TOPAS-5\sg\p1.sg 4228
Magnetic moment mlz of site Co1 cannot be refined as it has no derivative

This is my INP file
This
str
phase_name "nuclear"
space_group "P1"
a !lpa_15 16.645701_0.000191
b !lpb_15 15.253487_0.000184
c lpc_15 3.686826`
al !lpal_15 90.05477_0.00516
be !lpbe_15 89.97054_0.00589
ga !lpga_15 90.03257_0.00700
volume 936.103`
scale scale_nuclear 0.0285600186`
r_bragg 7.3673367
CS_L(@, 36.74702`)
Phase_Density_g_on_cm3( 6.89852`)

str
phase_name "Phase_1_magnetic"
mag_only_for_mag_sites
mag_space_group P1
a lpa_15 16.645701_0.000191
b lpb_15 15.253487_0.000184
c =2*lpc_15;: 7.373652

al !lpal_15 90.05477_0.00516
be !lpbe_15 89.97054_0.00589
ga !lpga_15 90.03257_0.00700
volume 936.103`
scale =scale_nuclear;: 0.0285600186`
r_bragg 100
CS_L(@, 20.00000`_LIMIT_MIN_0.3)
site Co1 A1(!xCo1 , 0.75420 ,0.75142) A2(!yCo1 , 0.86543, 0.86190) A3(!z1Co1 , 0.00805, 0.01289) occ Co 1.000 beq !valCo 0.43764_0.02010
mlx 0.00000 mly 0 mlz mlzz 0 MM_CrystalAxis_Display( 0.00000, 0.00000, 0.00000)
………
site Co16 A1(!xCo9 , 0.50091 ,0.50075) A2(!yCo9 , 0.36968, 0.36981) A3(!z1Co9 , 0.02375, 0.01726) occ Co 1.000 beq !valCo 0.43764_0.02010
mlx 0.00000 mly 0 mlz mlzz= mlzz16;: 0 MM_CrystalAxis_Display( 0.00000, 0.00000, 0.00000)

Secound I see point 3 of the mag example at
http://community.dur.ac.uk/john.evans/topas_workshop/tutorial_lamno3_…
I created a separate magnetic supercell with new a(mag)=b(nuclear), b(mag) = a(nuclear), c(mag) = 2c(nuclear).
Question1, I refine the nuclear structure by allowing each of a1 to a204 to refine. Their amplitudes will not be close to zero ,does it mean that our nuclear model is not good?
Question2, I tried to run TOPS and it is feasible，Although the results obtained were not very good. When I want to export its magnetic structure observation, it was not acceptable.I used this command http://topas.dur.ac.uk/topaswiki/doku.php?id=out_cif_mag

Thanks
Lijia

johnsoevans

One problem is that you don't have any sites in your nuclear structure, just magnetic.
If you try and refine 204 displacive mode amplitudes (equivalent to 204 xyz coordinates) the refinement is very likely to give non zero values as the an parameters will be highly (infinitely) correlated. At the very least some will be describing a floating origin in p1.

lijia-zhou

Dear john

I tried to add the atomic position in the nuclear phase, and then went to the finishing, it was able to run, but the magnetic information did not run very well, the result was 0. I think there should be a problem with my magnetic structure.
I also encountered a very big problem. I used the idea of symmetric mode to refine it. This method is very effective, but I can't export the magnetic structure model. I am trying to export the magnetic structure model using Out_CIF_mag.

macro Out_CIF_mag(file) {
out file
Out_String("data_topas_output")
Out(Get(sp_grp_char), "\n\n_mag_space_group_BNS_number %s")
Out(Get(a), "\n_magnetic_cell_length_a %V")
Out(Get(b), "\n_magnetic_cell_length_b %V")
Out(Get(c), "\n_magnetic_cell_length_c %V")
Out(Get(al), "\n_magnetic_cell_angle_alpha %V")
Out(Get(be), "\n_magnetic_cell_angle_beta %V")
Out(Get(ga), "\n_magnetic_cell_angle_gamma %V")

Out_String("\n\nloop_")
Out_String("\n_magnetic_space_group_symop_id")
Out_String("\n_magnetic_space_group_symop_operation_xyz")
Out_String("\n_magnetic_space_group_symop_operation_mxmymz")
Out_String("\n_magnetic_space_group_symop_operation_timereversal")
Out(Get(mag_sp_xyzs_txt), "%s")

Out_String("\n\nloop_")
Out_String("\n_magnetic_atom_site_label")
Out_String("\n_magnetic_atom_site_type_symbol")
Out_String("\n_magnetic_atom_site_fract_x")
Out_String("\n_magnetic_atom_site_fract_y")
Out_String("\n_magnetic_atom_site_fract_z")
Out_String("\n_magnetic_atom_site_occupancy")
Out_String("\n_magnetic_atom_site_B_iso_or_equiv")
atom_out file append
load out_record out_fmt out_eqn
{
"\n%s" = Get_From_String(Get(current_atom), site);
" %s" = Get_From_String(Get(current_atom), atom);
" %V" = Get_From_String(Get(current_atom), x);
" %V" = Get_From_String(Get(current_atom), y);
" %V" = Get_From_String(Get(current_atom), z);
" %V" = Get_From_String(Get(current_atom), occ);
" %V" = Get_From_String(Get(current_atom), beq);
}

out file append
Out_String("\n\nloop_")
Out_String("\n_magnetic_atom_site_label")
Out_String("\n_magnetic_atom_site_moment_crystalaxis_mx")
Out_String("\n_magnetic_atom_site_moment_crystalaxis_my")
Out_String("\n_magnetic_atom_site_moment_crystalaxis_mz")
atom_out file append
load out_record out_fmt out_eqn
{
"\n%s" = Get_From_String(Get(current_atom), site);
"%11.5f" = Get(a) Get_From_String(Get(current_atom), mlx);
"%11.5f" = Get(b) Get_From_String(Get(current_atom), mly);
"%11.5f" = Get(c) Get_From_String(Get(current_atom), mlz);
}
}

When I enter this macro setting, it is operational, but I can't get the file for the structural model.

Thanks

Lijia