Component Manual for the Neutron Ray-Tracing Package McStas, version 3.9

14.75  The SpinWave_BCO McStas Component

A sample for FM and AFM magnon scattering from a oI lattice based on cross section expressions from Marshall and Lovesey ch.9.

Identification

Description

Single-cylinder shape. Absorption included. No multiple scattering. No incoherent scattering emitted. No attenuation from coherent scattering. No Bragg scattering. Bravais lattice only. (i.e. just one spin per sublattice unit cell)

Algorithm: 0. Always perform the scattering if possible (otherwise ABSORB) 1. Choose direction within a focusing solid angle 2. Choose mode seperated by applied B-field 3. Calculate the zeros of (E_i-E_f-hbar omega(kappa)) as a function of k_f 4. Choose one value of k_f (always at least one is possible!) 5. 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

1

sigma_inc

barns

Incoherent scattering cross section per atom

0

a1

Å

Lattice constants of orthorhombic body centred lattice

a2

Å

Lattice constants of orthorhombic body centred lattice

a3

Å

Lattice constants of orthorhombic body centred lattice

j

meV

Coupling constant to body centered spins

ja

meV

Coupling constant to nearest neighbours along a

jb

meV

Coupling constant to nearest neighbours along b

jc

meV

Coupling constant to nearest neighbours along c

j_110

meV

Coupling constant to nearest neighbours +x+y

0

j_110_prime

meV

Coupling constant to nearest neighbours +x-y

0

S

1

Spin of magnetic ions

D

meV

Uniaxial anisotropy; easy axis is c-axis. Non-positive value assumed

B

T

Field strength of external magnetic field applied along z-axis

FM

1

Tag for ferromagnetic system if FM==1

0

Fq

1

Magnetic form factor

1

mode_input

1

Index of mode(s) to simulate

2

DW

1

Debye-Waller factor

1

T

K

Temperature

e_steps_low

1

Number of low-energy steps in zrid

e_steps_high

1

Number of high-energy steps in zrid

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

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

1

Verbosity level

0

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