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.

1. Magnetic symmetry
   • Magnetic symmetry operations
   • Magnetic point groups
   • Magnetic line groups
   • Magnetic plane groups
   • Magnetic space-groups
   • Magnetic superspace groups
   • Magnetic subperiodic groups
2. 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
3. Magnetic structure
   • Structure types (with examples)
   • Parameterization
     • Commensurate k-vectors
       • Wave approach
       • Supercell approach
       • Representational approach
     • Incommensurate k-vectors
       • Wave approach
       • Representation approach
   • The practical application of magnetic symmetry
   • Magnetic domains
4. Magnetic physical property tensors