We introduce and explain the magnetic structure analysis capabilities of the crystallographic computing program JANA2020. JANA2020 is a widely used tool for solving and refining crystal structures, including regular, twinned, modulated, and composite materials, utilizing X-ray, neutron, and electron diffraction data. One of its advanced features allows for determining and describing magnetic structures from powder and single-crystal neutron diffraction experiments. This capability is crucial for materials where the arrangement of magnetic moments (spins) becomes ordered below a certain temperature, resulting in magnetic phases essential in fundamental physics and practical applications, such as magnetic materials and devices.
The magnetic option in JANA2020 uses concepts of magnetic symmetry, including magnetic space groups and superspace groups, to handle commensurate (periodic) and incommensurate (modulated) magnetic structures. The program can simultaneously refine the atomic (nuclear) and magnetic structures, considering the symmetry constraints and how magnetic moments are distributed throughout the crystal. The article explains the mathematical foundation for calculating magnetic structure factors, essential for interpreting neutron diffraction data and distinguishing between nuclear and magnetic scattering contributions.
JANA2020 is unique in its ability to handle complex cases, such as modulated magnetic structures where the magnetic ordering does not follow the same periodicity as the atomic lattice, and even cases where magnetic and structural modulations are coupled. The program supports group-representation analysis and magnetic symmetry approaches, allowing users to test and refine different models against experimental data. The article also presents several examples of real magnetic structures solved using JANA2020, illustrating its power and flexibility in analyzing various magnetic materials.
Figure: Symmetry restrictions as presented in the magnetic option of JANA2020 for the magnetic structures of (a,b) Dy2Co3Al9 (commensurate, 2 K) (Gorbunov et al., 2018) and (c,d) Ho3Co (incommensurate, 18 K) (Goswami et al., 2024). The listing of restrictions used during refinements can be consulted for each magnetic atom through the button ‘Show symmetry restrictions’ (a,c); or for all magnetic (and non-magnetic) atoms in the unit cell in the refinement listing (b,d).