# ITC Volume M

An exploratory outline of a future volume on magnetic structures for the International Tables of Crystallography, based on commission discussions that began during summer 2013. Moved here on 22/04/15 from the old CMS Wiki, which is no longer supported. External input is welcome.

- Magnetic symmetry
- Magnetic symmetry operations
- Magnetic point groups
- Magnetic line groups
- Magnetic plane groups
- Magnetic space-groups
- Magnetic superspace groups
- Magnetic subperiodic groups

- Magnetic scattering (both x-rays and neutrons)
- Magnetic cross sections
- Magnetic form factors
- Magnetic diffraction experiments
- Polycrystalline (powder) neutron diffraction
- This is probably the largest and most important group.
- The results are often over interpreted and conclusions may not be unique.
- Much of directional info and interaction with external constraints is lost.
- Can be used with or without incident-beam polarization.

- Single-crystal diffraction with unpolarised neutrons
- Requires relatively large crystals (~0.5mm^3)
- Allows collection of larger data sets leading to less ambiguity.
- Magnetic domains may cause problems.
- Experiments using external constraints are possible (e.g. magnetic field, electric field, uniaxial stress)

- Single crystal diffraction with polarised neutrons: polarisation dependence of the scattered intensity
- Employ either incident or scattered beam polarizers.
- Details of magnetisation distribution
- Separation of magnetic and nuclear scattering
- Structural response to applied constraints
- Not for Laue experiments due to lack of good white-beam polarizers.

- Single-crystal diffraction with polarisation analysis
- Employ both incident and scattered beam polarizers.
- The experimental relationship between polarisation directions of the incident and scattered beams has three common varieties.
- Uniaxial: Pi and Pf are parallel
- XYZ: Allows diagonal elements of the polarisation matrix to be determined
- Spherical: Allows determination of all elements of the polarisation matrix

- Unique confirmation of moment directions relative to crystal axes and external constraints.
- Fine details of complex structures

- Diffuse neutron scattering from disordered or nanoscale materials
- Pair-distribution-function analysis of local magnetic order
- Small-angle scattering from mesoscopic magnetic order
- Reflectometry studies of magnetic films and surfaces

- Q-omega neutron spectroscopy of dynamic magnetic structures
- Resonant X-ray magnetic scattering
- Non-resonant X-ray magnetic scattering

- Polycrystalline (powder) neutron diffraction

- Magnetic structure
- Structure types (with examples)
- Parameterization
- Commensurate k-vectors
- Wave approach
- Supercell approach
- Representational approach

- Incommensurate k-vectors
- Wave approach
- Representation approach

- Commensurate k-vectors
- The practical application of magnetic symmetry
- Magnetic domains

- Magnetic physical property tensors