spinw.structfact method

calculates magnetic and nuclear structure factor

Syntax

sFact = structfact(obj, kGrid,Name,Value)

sfTable = structfact(obj, kGrid,Name,Value)

Description

sFact = structfact(obj, kGrid,Name,Value) returns the calculated structure factors in units of barn. Magnetic structures (FM, AFM and helical) are checked against FullProf. The structure factor includes the site occupancy and Debye-Waller factors calculated from obj.unit_cell.biso, using the same definition as in FullProf.

Input Arguments

obj: spinw object.
kGrid: Defines the reciprocal lattice vectors where the structure factor is to be calculated. For commensurate structures these are the possible positions of the magnetic Bragg peaks. For incommensurate helical/conical structures 3 Bragg peaks positions are possible: $$(\mathbf{k}-\mathbf{k}_m,\mathbf{k},\mathbf{k}+\mathbf{k}_m) around every reciprocal lattice vector. In this case still the integer positions have to be given and the code calculates the intensities at all three points.

Name-Value Pair Arguments

'mode'

String, defines the type of calculation:

mag Magnetic structure factor and intensities for unpolarised neutron scattering.
nucn Nuclear structure factor and neutron scattering intensities.
nucx X-ray scattering structure factor and intensities.

'sortq'

Sorting the reflections according to increasing momentum value if true. Default is false.

'formfact'

If true, the magnetic form factor is included in the structure factor calculation. The form factor coefficients are stored in obj.unit_cell.ff(1,:,atomIndex). Default value is false.

'formfactfun'

Function that calculates the magnetic form factor for given $Q$ value. value. Default value is @sw_mff, that uses a tabulated coefficients for the form factor calculation. For anisotropic form factors a user defined function can be written that has the following header:

F = formfactfun(atomLabel,Q)

where the parameters are:

F row vector containing the form factor for every input $Q$ value
atomLabel string, label of the selected magnetic atom
Q matrix with dimensions of $[3\times n_Q]$ , where each column contains a $Q$ vector in $Å^{-1}$ units.

'gtensor'

If true, the g-tensor will be included in the structure factor calculation. Including anisotropic g-tensor or different g-tensor for different ions is only possible here.

'lambda'

Wavelength. If given, the $2\theta$ value for each reflection is calculated.

'dmin'

Minimum $d$ -value of a reflection, all higher order reflections will be removed from the results.

'output'

String, defines the type of the output:

struct Results are returned in a struct type variable, default.
table Results are returned in a table type output for easy viewing and exporting.

'tol'

Tolerance of the incommensurability of the magnetic ordering wavevector. Deviations from integer values of the ordering wavevector smaller than the tolerance are considered to be commensurate. Default value is $10^{-4}$ .

'fitmode'

Speed up the calculation for fitting mode (omitting cloning the spinw object into the output). Default is false.

'fid'

Defines whether to provide text output. The default value is determined by the fid preference stored in swpref. The possible values are:

0 No text output is generated.
1 Text output in the MATLAB Command Window.
fid File ID provided by the fopen command, the output is written into the opened file stream.

Output Arguments

sFact

Structure with the following fields:

F2 Magnetic structure factor in a matrix with dimensions $[3\times n_{hkl}]$ .
Mk Square of the 3 dimensional magnetic structure factor, dimensions are: $[n_{ext}(1)\cdot f_{ext}(1)\times n_{ext}(2)\cdot f_{ext}(2)\times n_{ext}(3)\cdot f_{ext}(3)]$ , where $n_{ext}$ is the size of the extended unit cell.
hkl Contains the input $Q$ values in a matrix with dimensins of $[3\times n_{hkl}]$ .
hklA Same as hkl, but in Å $^{-1}$ units in the $xyz$ Cartesian coordinate system.
incomm Whether the spectra calculated is incommensurate or not.
formfact Cell containing the labels of the magnetic ions if form factor in included in the spin-spin correlation function.
{tth} $2\theta$ value of the reflection for the given wavelength, only given if a wavelength is provided.
obj Clone of the input obj object.

sfTable

Table, optional output for quick viewing and saving the output into a text file.