2014 Triennial Report of the Commission on Magnetic Structures
The IUCr Commission for Magnetic Structures was established by the General Assembly at the last triennial congress (Madrid, Spain, 2011). This new commission’s consideration encompasses a broad range of magnetic structure types, including commensurate magnetic structures, modulated and otherwise aperiodic magnetic structures, low-dimensional magnetic structures, disordered magnetic structures, etc. The original terms of reference presented with the request to create the commission are as follows:
- Establish standards for the description and dissemination of magnetic structures and their underlying symmetries (representations of propagation vector group, ‘complete’ representation of the group necessary for multi-k structures, 3D magnetic Shubnikov space groups, superspace symmetry … ), and promote these standards within the IUCr and among other research communities that rely on magnetic structure information.
- Develop CIF standards for magnetic structures and promote their use in crystallographic software. This activity will be developed in collaboration with the IUCr Committee for the Maintenance of the CIF Standard (COMCIFS).
- Develop a database for magnetic structures based on the sharing of magnetic CIF files.
- Cooperate with other IUCr Commissions in establishing and maintaining standards of common interest, such as magnetic symmetry-group tables, magnetic nomenclature and magnetic form factor data.
- Encourage communication and cultivate consensus among research communities that have independently developed diverse approaches to characterizing and describing magnetic structures.
- Promote the sponsorship and organization of magnetic-structure sessions, symposia, workshops and schools at triennial congresses of the IUCr, at the meetings of its Regional Associates, and at the meetings of other professional societies that tend to rely heavily on magnetic structure information. This should include sessions dedicated to the analysis of neutron scattering data and magnetic X-ray scattering data.
Following the inaugural commission meeting at the IUCr Congress in Madrid in August 2011, the CMS has conducted its business primarily through email correspondence. We have also conducted two internet-video conferences that spanned 16 time zones (10th October 2013 and 11 February 2014).
In 2012, the CMS reviewed and approved the new book, Magnetic Group Tables, authored by commission member Daniel Litvin (Pennsylvania State University, USA) for online publication by the IUCr. These extensive tables contain almost twelve thousand pages of tabulated data and graphics, which include magnetic point groups in 1, 2 and 3 dimensions, magnetic space groups in 1, 2 and 3 dimensions, magnetic Frieze groups, magnetic rod groups and magnetic layer groups. The data presented for each group includes graphical and tabulated information following the format of the International Tables of Crystallography Volume A, and also includes standard sets of coset representatives, maximal subgroups of index , and a comparison of Belov-Neronova-Smirnova and Opechowski-Guccione symbols. The tables are accompanied by a 100-page book, which contains examples that guide the user in the interpretation and use of each type of table. This monumental work took many years to complete, and is of great value to all who work with magnetic symmetry and/or magnetic structures. The complete tables are made freely available at http://www.iucr.org/publ/978-0-9553602-2-0 as part of the celebration of the 2014 International Year of Crystallography.
Near the end of the year, the CMS created a new website at https://magcryst.org, which in addition to providing basic information about the commission and its activities, provides a flexible means of advertising and supporting a variety of conferences and workshops. In addition to specific pages for events organized, sponsored, or otherwise advertised by the commission, we also provide an extensive list of othe meetings where high-quality magnetic-structure research is to be presented (https://magcryst.org/meetings/).
In 2012, the CMS conducted a review of the coordinate systems used to describe magnetic structures, and of the refinement packages that implement each one. The system that employs projections of the moment (in Bohr-magneton units) onto the possibly non-orthogonal axes of the unit cell is favored for publication and dissemination, though each of the other systems can be important in computations and some intuitive descriptions. A summary of this discussion is available on the commission wiki at http://cmswiki.byu.edu/wiki/Magnetic_Coordinates.
During the past three years, the commission has actively discussed three common methods of describing a magnetic structure: the supercell description, the wave description (a.k.a. propagation-vector description), and the representational (group-theoretical) description. Each description type has a distinct parameter set, which if treated in a fully general way, can be converted into any of the other descriptions. And each description can be executed with or without taking magnetic symmetry into account. We are working to define the minimal components that make each description complete and unambiguous, and to define standard procedures for converting between different descriptions. Such standards will make the communication of magnetic structures much more reliable. The commission has already begun to discuss an outline for a new volume of the International Tables that would focus on magnetic tructures, though there is much to do before undertaking this project.
In 2013, we saw a great deal of software development in support of magnetic symmetry and various types of magnetic structural analysis, examples being FULPROF, JANA, the Bilbao Crystallographic Server, and the ISOTROPY suite. As these tools continue to develop and interact, the importance of the pending magnetic CIF standard is growing. Commission efforts to establish the most basic components of a magnetic CIF dictionary that accomodates both commensurate and incommensurate magnetic structures have intensified in early 2014. A first-draft proposal to COMCIFS should be ready prior to the 2014 Congress in Montreal. Based on these developments, J. Manuel Perez-Mato and his colleagues at UPV/EHU in Bilbao have begun the difficult task of preparing an online database of magnetic structures, which is expected to utilize the new magnetic CIF standard. Primary resources in this effort include the book “Magnetic structures determined by neutron diffraction” by Andrzej Oles, and the structure collection of Wieslawa Sikora. We note the recent passing (18 January 2014) of Professor Oles with sadness.
From 2011 to 2013, the members and consultants of the CMS have furthered the goals of the commission through the organization, sponsorship or support of conferences, symposia, workshops, schools and courses at nearly 25 research venues covering a broad range of topics. Many of these meetings were not specifically organized under the auspices of the commission, but substantially furthered its objectives of promoting magnetic neutron scattering and magnetic structure determination. At most of these events, commission members and consultants played a key organzational role.
Wieslawa Sikora (AGH University of Science and Technology, Krakow, Poland) represented our commission on the International Program Committee of the 2014 IUCr Congress. At the spring-2013 IPC meeting in Montreal, she was instrumental in the planning of an impressive array of lectures and microsymposia related to magnetic crystallography (https://magcryst.org/meetings/iucr-congress-2014/). This will be an exciting and important congress for researchers in this field.
In celebration of the International Year of Crystallography, the CMS has also organized a three-day workshop on “The Role of Magnetic Symmetry in the Description & Determination of Magnetic Structures” (https://magcryst.org/meetings/cmsworkshop2014). This sattelite meeting of the 2014 IUCr Congress will be held on 14-16 August 2014 at the Brockhouse Institute for Materials Research at McMaster University, which is located in the city of Hamilton near Toronto, Canada. In addition to addressing the theoretical foundations of magnetic crystallography, the workshop will include hands-on software tutorial sessions and a number of applications lectures that demonstrate the effective of magnetic symmetry to simplify structural description and analysis.
Branton J. Campbell