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McStas: Magnon_bcc

[ Identification | Description | Input 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

  • Site:
  • Author: Kim Lefmann
  • Origin: KU
  • Date: 23.10.08 - 24.07.18

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.
NameUnitDescriptionDefault
radiusmOuter radius of sample in (x,z) plane
yheightmHeight of sample in y direction
sigma_absbarnsAbsorption cross section at 2200 m/s per atom
sigma_incbarnsIncoherent scattering cross section per atom
aAAbcc Lattice constant
FM1Flag for whether the order if FM (0 means AFM)0
J1meVspin-spin interaction 1 (nn)
J2meVspin-spin interaction 2 (nnn)
Dmevsingle ion anisotropy
s1spin
DW1Debye-Waller factor
TKTemperature
target_xmposition of target to focus at . Transverse coordinate0
target_ymposition of target to focus at. Vertical coordinate0
target_zmposition of target to focus at. Straight ahead.0
target_index1relative index of component to focus at, e.g. next is +10
F21magnetic form factor squared1
focus_rmRadius of sphere containing target.0
focus_xwmhoriz. dimension of a rectangular area0
focus_yhmvert. dimension of a rectangular area0
focus_awdeghoriz. angular dimension of a rectangular area0
focus_ahdegvert. angular dimension of a rectangular area0
verbose1flag for test printing (print if verbose==1)0
AT ( , , ) RELATIVE
ROTATED ( , , ) RELATIVE

Links


[ Identification | Description | Input parameters | Links ]

Generated on 2024-01-03 11:47:43


Last Modified: Wednesday, 03-Jan-2024 19:59:11 CET
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