This tutorial will walk you through how to simulate the dipole fields in probable low-moment ferromagnet Ba₂NaOsO₆, and thus obtain constraints on the size of the magnetic moments, using MµCalc. The analysis detailed here was published in //Physical Review B// (PRB 84 144416 (2011), arXiv:1103.1039). A more detailed version of the analysis is available in Andrew Steele’s thesis, in Chapter 4, Low-moment magnetism in Ba₂//M//OsO₆ (//M// = Li, Na). (Please note that the additional analysis relating to rotating moments to obtain their probable direction is not currently available via the MµCalc user interface, and had to be performed by modifying the source code.)

An [Install MµCalc](old tutorial]], explaining how to use MµCalc for pre-Bayesian, simple examination of a crystal structure for sites with fields corresponding to the observed frequencies in an experiment, is available for reference.

[[install), then launch it: open a terminal window and navigate to the installation directory; then type ''python mmcalc.py'' and press enter.

All commands are issued by typing a letter (case-insensitive). (On a few operating systems or terminals this may need to be followed by enter.) c opens the crystal menu.

(S) space group (not set) (U) length unit (not set) (A) a (not set) (B) b (not set) (C) c (not set) (1) alpha (not set) (2) beta (not set) (3) gamma (not set) (T) atoms (not set) (M) magnetic properties (D) draw crystal (V) save crystal (L) load crystal (Q) back to main menu

Please choose an option by pressing the letter

Enter each piece of structural information by pressing the relevant letter followed by enter. You will be presented with an input screen. Enter the value required; MµCalc should alert you with an error message if the value you enter is invalid.

The structural data for Ba₂NaOsO₆ were obtained from

• The space group is $Fm\bar{3}m$; barred values are entered as a hyphen-minus followed by the number, so enter ''Fm-3m'' or, alternatively, the space group number, ''225''.
• Choose a length unit. Nanometres are preferred since they are SI and still relatively convenient, but angstroms and metres are possible alternatives. To enter lengths in metres, use (scientific) e notation; for example, 0.4426 nm would be 4.426e-10.
• $a = b = c = 0.4426\text{ nm}$
• $α = β = γ = 90°$

Next, you must add atoms in the atoms menu. This deals with fractional coordinates and electrical charge((The charge information entered does not currently serve any purpose, so feel free to ignore that if you do not have that information for your compound!)); magnetic properties are specified in a more general way later. Add atoms with the following parameters:

• Ba, $x = y = z = 0.25$, $q = +2|e|$
• Na, $x = y = z = 0.5$, $q = +1|e|$
• Os, $x = y = z = 0$, $q = +7|e|$
• O, $x = 0.5, y = z = 0$, $q = -2|e|$

After adding these, your atom menu should look like this:

1            Mn           0.0          0.0          0.0          2            
2            O            0.5          0.0          0.0          -2           

 (A)  add atom
 (D)  delete atom
 (E)  edit atom
 (Q)  back to crystal menu

Please choose an option by pressing the letter 

You have now entered all of the required structural information, and the crystal menu should look like this:

 (U)  length unit (nm)
 (A)  a (= 0.4426 nm)
 (B)  b (= 0.4426 nm)
 (C)  c (= 0.4426 nm)
 (1)  alpha (= 90.0°)
 (2)  beta (= 90.0°)
 (3)  gamma (= 90.0°)
 (T)  atoms (MnO)
 (M)  magnetic properties
 (D)  draw crystal
 (V)  save crystal
 (L)  load crystal
 (Q)  back to main menu

Please choose an option by pressing the letter

FIXME The above still refers largely to MnO, and there's more to add below...

High-five a colleague. You're done!

Further to the paper listed previously (PRB, arXiv), the Ba₂//M//OsO₆ system is examined in more detail in Chapter 3 of Andrew Steele's DPhil thesis. Chapter 2 of his thesis also contains useful background about dipole field simulation, and the Bayesian technique used in this analysis.