2020 Triennial Report of the IUCr Commission on Magnetic Structures
Following the Montreal Congress in August 2017, the voting members of the commission include Branton Campbell (Chair, USA), Maxim Avdeev (Australia), Maria Teresa Fernandez-Diaz (France), Ovidu Garlea (USA), Margarida Henriques (Czech Republic), J. Manuel Perez-Mato (Spain), Juan Rodriguez-Carvajal (France), Taku Sato (Japan), Andrew Wills (UK), and Oksana Zaharko (Switzerland). The commission’s consultants include: Mois Aroyo (Spain), Javier Campo (Spain), Daniel Litvin (USA), Alexander Pirogov (Russia), and Wieslawa Sikora (Poland). Following the congress in Hyderabad, it was decided that in the coming term, J. Manuel Perez-Mato would serve as Secretary of the commission, Danny Litvin would continue to serve as liaison to the Commission for Nomenclature, and Maria-Teresa Fernandez-Diaz would continue to serve as liaison to the Commission on Neutron Scattering.
53rd International School of Crystallography
The commission organized and conducted the 53rd course of the International School of Crystallography at the Ettore Majorana Research Foundation in Erice, Italy, on the subject of Magnetic Crystallography (https://crystalerice.org/2019/welcome.php), during the ten days from May 31st to June 9th of 2019.
Commission members who participated in organization and/or lectures and workshops:
- Branton Campbell (Brigham Young University, USA) – science director
- Maria Teresa Fernandez-Diaz (Institut Laue-Langevin, France) – science director
- Manuel Perez-Mato (Unversidad del Pais Vasco, Spain) – science director
- Maxim Avdeev (ANSTO Australian Center for Neutron Scattering, Australia)
- Ovidiu Garlea (ORNL Neutron Scattering Division, Oak Ridge, USA)
- Margarida Henriques (CAS Institute of Physics, Prague, Czech Republic)
- Vaclav Petricek (CAS Institute of Physics, Prague, Czech Republic)
- Juan Rodriguez-Carvajal (Institut Laue-Langevin, Grenoble, France)
- Taku Sato (Tohoku University, Tohoku, Japan)
- Andrew Wills (University College London, London, UK)
- Oksana Zaharko (Paul Scherrer Institut, Villigen, Switzerland)
Others who contributed lecture and workshop presentations:
- Laurent Chapon (Diamond Light Source, Didcot, UK)
- Luis Elcoro (University of the Basque Country, Bilbao, Spain)
- Oscar Fabelo (Institut Laue-Langevin, Grenoble, France)
- Dmitry Khalyavin (RAL ISIS Facility, Didcot, UK)
- Harold Stokes (Brigham Young University, Provo, USA)
- Robert Von Dreele (ANL Advanced Photon Source Argonne, USA)
The local organizing team was led by Annalisa Guerri (University of Florence, Italy) and Paola Spadon (University of Padova, Italy), and included computing and technical support from Andrea Giaccherini (University of Florence, Italy), Andy Stewart (University of Limerick, Ireland), and Erin Davis (USA).
The school was advertised internationally, with a special emphasis on reaching out to researchers in countries that are not typically well represented at such meetings. There were no restrictions on geographical affiliations of the participants. From among the roughly 100 applicants, 64 participants (not including the presenters) were selected based on their preparation and ability to benefit from attendance; this was the maximum number that facility-space limitations allowed. The participants and presenters came from 25 different nationalities and country affiliations, more than half of which were outside of Western Europe or North America. There were significant numbers from each of Russia and Eastern Europe, Asia, South America, and India. More than one third of the attendees were women.
The magnetic-crystallography program was organized to address key advances in magnetic-structure research, as well as the foundational and state-of-the-art of theoretical, experimental, and computational capabilities that made these advances possible. The school included a roughly 50/50 combination of lectures and hands-on workshops. Three hours of workshops were held each morning, with two sessions conducted in parallel. The state-of-the art computational tools represented in the workshops included FullProf, JANA 2006, SARAh, the Bilbao Crystallography Server, the ISOTROPY Software Suite, GSAS-II, and TOPAS. Both introductory and advanced tutorial exercises were provided, in order to fully engage beginners and experts alike. Three hours of lectures were presented each afternoon. Topics included the experimental determination and communication of magnetic structures, the theoretical and mathematical foundations of magnetic symmetry and representational analysis, and a wide variety of applications. Each of the 17 presenters, in addition to contributing a lecture, also provided lecture notes in manuscript form. The technical program ended with a one-hour panel discussion of questions submitted by the participants.
Of 40 submitted participant abstracts, 10 were selected for oral presentations (22 minutes or 15 minutes), including Shivani Sharma (JNCASR, Bengaluru, India), Anna Matveeva (Petersburg Nuclear Physics Institute, Gatchina, Russia), Jose Luis Garcia-Munoz (ICMAB-CSIC, Barcelona, Spain), Stephanie Gneuwuch (U. Maryland, USA), Anuradha Vibhakar (U. Oxford, UK), Elena Solana Madruga (U. Edinburgh, UK), Stefanie Siebeneichler (Stockholm U., Sweden), Fernando Pomiro (U. Warwick, UK), Claire Colin (Institut Néel, U. Grenoble-Alpes, France), and Francoise Damay (Laboratoire Léon Brillouin, Gif-sur-Yvette, France). The two poster sessions for participant research were also of very high quality and were well attended during the school. Three of these posters were selected by a panel of judges for awards, which were presented during the closing ceremony, which included Premakumar Yanda (JNCASR, Bengaluru, India), Rebecca Scatena (U. Bern, Switzerland), and Guru Khalsa (Cornell U., USA).
To facilitate interaction between and among the participants and presenters, the school included a rich social program, which included several social dinners, an evening with local musicians and performers, excursions to historical sites in the region, and daily lunch and coffee breaks. In the relaxed atmosphere, the organizers attempted to become personally acquainted with each participant. We are confident that the school initiated many long-term friendships and collaborations.
Preparations for the IUCr Congress in Prague
In preparation for the IUCr Congress in Prague, the commission met online to brainstorm, select, and prioritize topics potential topics. Then, in May 2019, Oksana Zaharko, our representative to the International Planning Committee, traveled to Prague to negotiate the final program. Her outstanding efforts and negotiation skills made it possible to organize 15 sessions with magnetic-structure themes or components, among which 9 microsymposia and 3 keynote lectures were sponsored or co-sponsored by the commission (listed below). Oksana’s invaluable service on the IPC is greatly appreciated by all.
- Methods and software developments for magnetic-structure analysis (MS-22)
- Magnetic structures of novel and functional materials (MS-30)
- Topological magnetic order and quasiparticles (MS-87)
- Magnetic structures at extreme conditions and in extreme samples (MS-61)
- Symmetry aspects of magnetic order and magnetic properties (MS-68)
- Frustrated magnetic order and emerging science (MS-45)
- Molecular magnets and metal-organic frameworks, including quantum cryst. approaches (MS-51)
- Structural, electronic and magnetic ordering: from fundamental physics to functionality (MS-38)
- New applications of coherent scattering (MS-40)
- The science of symmetry breaking, Stokes Harold (KN-35)
- Quantum crystallography and spintronic materials, Macchi Piero (KN-15)
- Dithiadiazolyl radicals as building blocks for molecular magnetic materials (KN-12)
For the IPC meeting in Prague, Oksana, together with B.J. Campbell, J. M. Perez-Mato, and T. Sato, submitted a manuscript on “Magnetic Structure Research, Future and Future Trends”, which was subsequently published in Materials Structure 26 (2), 97-100 (2019). (http://www.xray.cz/ms/bul2019-2/cms.pdf)
In early 2019, the commission advertised the IUCr Congress actively and widely within various magnetic-structure research communities, with special emphasis placed on identifying researchers in developing nations. Because the congress was postponed for a year due to the COVID-19 pandemic, this advertising thrust was repeated again in early 2020.
The magCIF working group actively discussed a variety of revisions to the standard magCIF dictionary that was developed by the commission in previous years: (1) Improvement of the descriptions of tags related to magnetic moments and incommensurate magnetic modulations. (2) Addition of a tag for the magnitude of a magnetic moment. (3) Creation of a new category for rotational moments (applicable to the pivot points of rigid units) that is highly analogous to that for magnetic moments. (4) Progress on categories for magnetic reflection data from diffraction experiments. (5) Debate on the possible addition of origin-referenced modulation parameters, as an alternative of the atom-referenced ones, which are currently used in the superspace formalism.
Also regarding the development of extended CIF standards for the communication of magnetic structures, the commission began work on the symmetry-mode CIF (smCIF) dictionary, which will standardize the concise and unambiguous description of magnetic and other symmetry-lowered crystal structures in terms of symmetry-modes (basis functions of matrix representations of the parent symmetry group, often referred to as representation analysis). The most efficient and complete approach to the description of a magnetic structure simultaneously employs both a magnetic symmetry group and symmetry-mode information, which are fully compatible. The smCIF dictionary will facilitate such descriptions. A first draft of the smCIF dictionary, including some examples, was proposed by Branton Campbell, and is now under discussion by an ad-hoc working group of interested people among the membership and the consultants of the commission. In accordance with our terms of reference, these CIF related activities have included communication with the chair of the COMCIFS commission, James Hester.
In 2018, Branton Campbell and Harold Stokes presented a proposal for an international-standard magnetic space-group symbol, and in 2020, Juan Rodriguez-Carvajal presented a related proposal for Hall symbols for magnetic space groups. Both proposals were discussed and debated by the commission, and improved by the feedback received. The magnetic Hall symbol concept recently appeared J. Appl. Cryst. (2021). 54, 338-342.
Software development and reference materials
Software and reference materials supporting the modeling, solution, refinement, and visualization of magnetic structures have seen significant development during the years 2018-2020. Commission participants contributed to much of this development.
The Bilbao Crystallographic Server upgraded the MTENSOR program to include magnetic phases, as reported in Acta Cryst. (2019) A75, 438-447. It now calculates the symmetry-adapted forms of physical-property tensors that include magnetic properties.
The Bilbao Crystallographic Server has continued to add to the MAGNDATA database of magnetic structures, which has grown rapidly to include roughly 1500 structures. Their team estimate this to be approximately 25% of the magnetic structures in the scientific literature which are sufficiently complete and unambiguous to catalog. An author-search feature has been added to the user interface, and a structure-submission feature for new structures is expected soon.
The first version of FullProf (version 7.00) able to refine magnetic structures (powder and single crystals) having up to three independent modulations within the superspace formalism was distributed in May 2019. The symmetry constraints on modulation functions was fully implemented for an arbitrary set of propagation vectors and harmonics. Spherical coordinates can be used to describe modulation amplitudes facilitating the use of extra-constraints beyond symmetry. Presently, only magnetic modulations are available, though displacive, occupational and ADP modulations will be also implemented in the future. The program outputs a magnetic P1-symmetry CIF file that can be directly read by VESTA to visualize a user-selected supercell. A conventional modulated mCIF file is also output with the refined magnetic structure. This file can be read by JMOL/MVISUALIZE to plot the magnetic structure.
Le Bail fits using superspace groups was also fully implemented in FullProf with an output adequate to perform, in a second stage, a simulated annealing run working with the full powder profile to solve magnetic structures ab initio. All modulation functions are included in the simulated annealing method with all kind of constraints compatible with the symmetry.
The program mCIF_to_PCR from the Bilbao Crystallographic Server has been extended to accommodate incommensurate structures with superspace-group symmetry. After importing a CIF from ISODISTORT, mCIF_to_PCR automatically allows one to prepare the input file for FullProf using a superspace groups in whatever setting.
The program WinPLOTR-2006 in the FullProf Suite has been modified in order to identify the different kind of reflections: nuclear, magnetic of mixed (up to six integer indices), when using superspace description.
SARAh was recently launched as a webApplication in order to stabilize its development base and move away from issues related to legacy Windows operating systems. As part of a goal to bring representational analysis calculations closer to the two-colour groups, the web version now determines isotropy groups and related magnetic point groups of the little group Gk for and their basis vectors, as well as those of the kernel calculations. Calculations can be done for commensurate and incommensurate structures alike.
GSAS-II now fully supports magnetic structures, including those with one incommensurate modulation. The search for a correct description of a magnetic structure is simplified in GSAS-II where a special version of the k-SUBGROUPSMAG tool from the Bilbao Crystallographic Server is called with the parent chemical space-group operations, selected k-vectors, and some option flags. The result is parsed by GSAS-II to extract the generated magnetic space groups, transformation matrices, origin shift vector, conjugacy classes (if any), and supergroup lists. GSAS-II also examines the magnetic atom positions to determine if any or all can carry a nonzero moment, flagging those space groups with atoms that can.
JANA2006 performs representation analysis for and commensurate cases based on the irreducible representation data published by H. T. Stokes, B. J. Campbell and R. Cordes, Acta Cryst. (2013). A69, 388-395. This allows it to use the same symbols as in ISODISTORT. The procedure for importing the models from ISODISTORT was considerably improved. Furthermore, Jana was upgraded to the new version, Jana 2020, which allows parallel refinement of several models. The graphical interface for the new Jana2020 has also been further developed.
In the ISOTROPY Software Suite, the symmetry-allowed forms of Wyckoff sites are now presented for magnetic and non-magnetic incommensurate structures. Magnetic and non-magnetic incommensurate symmetry groups have been fully implemented in both FINDSYM and ISOCIF, so that it is possible to detect the actual or pseudo symmetry (with tolerances on atomic parameters and Fourier coefficients) of an incommensurate structure. The magnetic superspace groups (MSSGs) with up to three modulations have now been fully enumerated for the first time, and have been incorporated into all of the modulation-capable software tools in the suite.
Structure and magnetic neutron diffraction (2020) by Alexander N. Pirogov and Mikhail A. Semkin, Ural University Publishing House, Ekaterinburg, 169 pages, provides a new Russian-language source of tutorial materials for students who are new to magnetic neutron diffraction.
During the years 2018-2020, the commission has encouraged high-quality magnetic-structure research through the support of roughly 30 national and international conferences, schools, and workshops. This support by the commission and its individual members and consultants has included sponsorship, direct meeting organization, grant writing, organization and/or chairing of conference sessions, workshop presentations, and both invited and contributed lectures.
Other plans or interests of the commission include the following:
(1) Expand efforts to educate the crystallographic and broader structural-science communities in the art of unambiguously and concisely describing a magnetic structure.
(2) Continue to promote the wide-spread adoption of the magCIF standard amongst crystallographic software developers.
(3) Extend magCIF to support magnetic structure factors, magnetic reflection conditions, low-dimensional magnetic order, short-range magnetic order, etc.
(4) Expand the MAGNDATA database of magnetic structures into an exhaustive resource.
(5) Support the development of tools that convert between OG and BNS presentations of a commensurate magnetic-structure (in magCIF format), and between commensurate-supercell and incommensurate-wave descriptions of a commensurate magnetic structure.
(6) Develop long-term strategies for supporting and preserving computational tools and data resources relevant to the determination and communication of magnetic structures.
(7) Prepare a new volume of the International Tables of Crystallography that focuses on magnetic symmetry, magnetic diffraction, and magnetic structures.
Branton J. Campbell (Commission Chair)
Manuel Perez-Mato (Commission Secretary)