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:

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

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.

See Also

sw_egrid | spinw | spinw.spinwave