sw_neutron#

Syntax#

spectra = sw_neutron(spectra,Name,Value)

Description#

spectra = sw_neutron(spectra,Name,Value) calculates the neutron scattering cross section for polarised and unpolarised neutrons. The function reads the calculated spin-spin correlation function \(\mathcal{S}^{\alpha\beta}(\mathbf{Q},\omega)\) and calculates the neutron scattering cross section for unpolarized neutrons using the formula:

\[S_\perp(Q,\omega)=\sum_{\alpha\beta}(1-\hat{q}^\alpha\hat{q}^\beta)\cdot S^{\alpha\beta}(Q,\omega)\]

It also calculates spin-spin correlation function in the Blume-Maleev coordinate system and the complete polarised neutron scattering cross section.

{% include note.html content=” The Blume-Maleev coordinate system is a cartesian coordinate system with \(x_{BM}\), \(y_{BM}\) and \(z_{BM}\) basis vectors defined as:
\(x_{BM}\) parallel to the momentum transfer \(Q\),
\(y_{BM}\) perpendicular to \(x_{BM}\) in the scattering plane,
\(z_{BM}\) perpendicular to the scattering plane. “ %}

Input Arguments#

spectra: Input structure, contains spin-spin correlation functions. Supported inputs are produced by spinw.spinwave, spinw.powspec and [spinw.scga].

Name-Value Pair Arguments#

'n': Normal vector to the scattering plane, in real space (\(xyz\) coordinate system), stored in a row vector with 3 elements. Default value is [0 0 1].
'uv': Cell, that contains two vectors defining the scattering plane in rlu. If given overwrites the n parameter value. For example: {[1 0 0] [0 1 0]} stands for the \((h,k,0)\) scattering plane.
'pol': If true the cross sections in the Blume-Maleev coordinate system will be also calculated (inP, Pab and Mab fields of the output spectra). Default value is false.

Output Arguments#

spectra

Same as the input spectra plus the following additional fields:

param Input parameters.
Sperp \(S_\perp(i_{mode},\mathbf{Q})\) unpolarised neutron scattering cross section, stored in a matrix with dimensions of \([n_{mode}\times n_{hkl}]\).
intP \(I_P(P_i,i_{mode},\mathbf{Q})\) polarised neutron scattering cross section, when only the incident neutron polarization is analyzed. It is stored in a matrix with dimensions of \([3\times n_{mode}\times n_{hkl}]\).
Pab \(I_{Pab}(P_f,P_i,i_{mode},\mathbf{Q})\) complete polarised neutron scattering cross section, when the polarisation of both the incident (\(P_i\)) and the scattered (\(P_f\)) neutrons are analyzed. Stored in a matrix with dimensions of \([3\times 3\times n_{mode}\times n_{hkl}]\).
Mab \(M_{ab}(P_f,P_i,i_{mode},\mathbf{Q})\) components of the spin-spin correlation function in the blume-Maleev coordinate system, stored in a matrix with dimensions of \([3\times \times3 n_{mode}\times n_{hkl}]\).

If several domains exist in the sample, Sperp, intP, Pab and Mab will be packaged into a cell, that contains \(n_{twin}\) number of matrices.

The meaning of the indices above:

\(P_i\): index of incident polarisation (\(1=x_{BM}\), \(2=y_{BM}\) or \(3=z_{BM}\)),
\(P_f\): index of final polarisation (\(1=x_{BM}\), \(2=y_{BM}\) or \(3=z_{BM}\)),
\(i_{mode}\): index of spin wave mode,
\(\mathbf{Q}\): index of momentum transfer.