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McStas: Magnon_bcc Component

[ Identification | Description | Input parameters | Output parameters | Links ]

The Magnon_bcc Component

A sample for AFM or FM magnon scattering based on cross section expressions from Squires, Ch.8.2

Identification

  • Author: Kim Lefmann
  • Origin: KU
  • Date: 23.10.08 - 24.07.18
  • Version:(Unknown)

Description

Single-cylinder shape.
Absorption included.
No multiple scattering.
No incoherent scattering emitted.
No attenuation from coherent scattering. No Bragg scattering.
bcc crystal n.n. and n.n.n. interactions only
Can do either FM or AFM order upon a flag
Assume J>0 for both FM and AFM. MUST BE CHANGED FOR CONSISTENCY
If AFM, the order is two-sublattice, e.g. the AFM Bragg ordering vectors are Q = (1 0 0) and equivalent.
One magnon branch only
Assume spin along z
Possible easy axis anisotropy along z
No external field

KNOWN BUGS:
Gives zero scattering for too large J values (for AFM J=0.362, h approx 1). Probably this is a malfunction of zridd or call thereof
The value of the absolute scattered intensity is clearly too high. This is probably due to unit confusion. The relative intensity scaling seems about right.

Algorithm:
0. Always perform the scattering if possible (otherwise ABSORB)
1. Choose direction within a focusing solid angle
2. Calculate the zeros of (E_i-E_f-hbar omega(kappa)) as a function of k_f
3. Choose one value of k_f (always at least one is possible!)
4. Perform the correct weight transformation

Input parameters

Parameters in boldface are required; the others are optional.
Name Unit Description Default
radius m Outer radius of sample in (x,z) plane  
yheight m Height of sample in y direction  
sigma_abs barns Absorption cross section at 2200 m/s per atom  
sigma_inc barns Incoherent scattering cross section per atom  
a AA bcc Lattice constant  
FM 0 means AFM [1] Flag for whether the order if FM 0
J1 nn [meV] spin-spin interaction 1  
J2 nnn [meV] spin-spin interaction 2  
D mev single ion anisotropy  
s 1 spin  
DW 1 Debye-Waller factor  
T K Temperature  
target_x m position of target to focus at . Transverse coordinate 0
target_y m position of target to focus at. Vertical coordinate 0
target_z m position of target to focus at. Straight ahead. 0
target_index 1 relative index of component to focus at, e.g. next is +1 0
F2 1 magnetic form factor squared 1
focus_r m Radius of sphere containing target. 0
focus_xw m horiz. dimension of a rectangular area 0
focus_yh m vert. dimension of a rectangular area 0
focus_aw deg horiz. angular dimension of a rectangular area 0
focus_ah deg vert. angular dimension of a rectangular area 0
verbose print if verbose==1 [1] flag for test printing 0

Output parameters

Name Unit Description Default
V_rho AA^-3 Atomic density  
V_my_s m^-1 Attenuation factor due to incoherent scattering  
V_my_a_v m^-1 Attenuation factor due to absorbtion  
DV  
parms  

Links


[ Identification | Description | Input parameters | Output parameters | Links ]

Generated automatically by McDoc, Peter Willendrup <peter.willendrup@risoe.dk> / Fri Oct 11 07:30:14 2019


Last Modified: Friday, 11-Oct-2019 09:30:14 CEST
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