Abstract

Keywords: Magnetic order, Phase transitions, Diffraction

Correspondence should be directed to: W.Sikora,
Faculty of Physics and Nuclear Techniques, University of Mining and Metallurgy,
al.Mickiewicza 30, 30-059 Krakow, Poland
e-mail: sikora@novell.ftj.agh.edu.pl
fax: (48)-12-340010

Short introduction to the Database of Magnetic Structures

The source files are orga8nized in a way related to the CIF standard [1]. The first set of data, concerning the crystallographic parameters of a given compund, uses the exact forms of CIF data names. The description concerns the paramagnetic phase (PF), right above the first magnetic phase transition and all the magnetic phases below. It includes: the symmetry space group, cell parameters and atomic positions with the corresponding measurement temperatures. The coordinate system used for description of the PF should be chosen according to the International Tables for Crystallography (ITC) [2].
Here you can see a filled CIF form used for the crystalline data. The remaining sets of data concern the description of the magnetically ordered phases found in the respective compound. For each magnetic phase a separate data set is built. The data files for a sequence of magnetic phases in one compound are labelled in the order of decreasing temperatures. The description of each magnetic phase is done in a coordinate system consistent with the respective crystallographic phase description. We present here both a vocabulary of magnetic keywords and a filled form used for the magnetic data.

The preliminary version of the entry forms has been discussed with the participants of "Workshop on Application of Symmetry Analysis ..." held in Krakow(Poland) in June 1996, and here we present the final form prepared after the ECNS'96 conference (held in Zurich).

The data files for each magnetic phase include:

• the temperature stability range
• the magnetic structure determination method
• the values of magnetic moments
• the magnetic unit cell (for commensurate structures) as multiplicity of crystallographic cell in x,y,z direction
• verbal magnetic structure description
• the orientations of magnetic moments (MM) at the respective atomic sites in the conventional crystallographic unit cell (the Mx, My, Mz components of MM vector or its length and the respective spherical angles)
• the specification of magnetic space group (according to Opechowski, Guccione [3]) or spin space group (according to Litvin, Opechowski [4])
• the description of the ordering wave vector (in two frames: one connected with unit cell reciprocal to conventional cell and second reciprocal to primitive cell) including the k-vector star (according to Kovalev [5]) or the symmetry point in the Brillouin zone (according to Miller-Love [6])
• the irreducible representation of the symmetry space group of the paramagnetic phase, connected with the considered magnetic ordering (named according to Opechowski [5] or Miller-Love [6])
• the symmetry based order parameters (given for each magnetic phase as the components of the respective magnetic structure in the symmetrized coordinate system e.g. as the coefficients of the linear combination of the basic vectors of the irreducible representation mentioned above).

For all the above data the respective references are given, when available. A sample reference list is presented here.

The information is presented by a program written in C++, providing a possibility to search the database using several various criteria (elements, symmetry group etc.). For the chosen magnetic phase the information is presented in three blocks: the crystalline data, the magnetic structure and the list of references. The display is splitted vertically into two windows, so that two data blocks (choosen by the user) can be seen at the same time. In each window the information can be scrolled up and down. When required a picture of crystalline unit cell or magnetic structure can be loaded into one of the windows. Here you can see:

• sample picture of a crystalline cell
• sample picture of the magnetic cell

Our intention is to distribute the database only as a datafile, presented by the program mentioned above. The reason for that is to provide the possibility of a permanent update and the correction of errors. We plan to distribute the package on the "registered users" basis with rather small registration fee. We expect the users to contribute to the database both by the filled in entry forms as well as the correction of data records. In our opinion the above rules should provide the required flexibility and also a form of quality control.

Acknowledgments

References:

• 1. S.R.Hall, F.H.Allen, I.D.Brown, Acta Cryst. A47 (1991), 655-685
• 2. International Tables for Crystallography, Volume A, ed. Theo Hahn, D.Reidel Publishing Company, Dordrecht/Boston 1983
• 3. W.Opechowski, R.Guccione, Magnetism, Voll.IIA, Eds. G.T.Rado and H.Suhl, Academic Press, NY, 1965
• 4. D.B.Litvin, W.Opechowski, Physica 76, 1974, 538-554
• 5. O.V.Kovalev, Representations of the Crystallographic Space Groups. ed.T.H.Stokes and D.M.Hatch,
  Gordon and Breach Science Publ., 1993
• 6. S.C.Miller, W.S.Love, Tables of Irreducible Representations of Space Groups ..., published by Pruett Press,
  Boulder Colorado 1967

To order the empty data forms by e-mail or just to send a comment you can send an e-mail to the authors at the

AGH Institute of Physics.

Distribution

Preliminary version of the presentation program, providing a possibility to browse the contents of the database, is already available. The program searches for the requested compound, shows the text description files and draws pictures of both crystalline and magnetic structure of the compund. Together with program a sample database is provided, including 30-40 compounds with rather simple magnetic structures. The preliminary version is not able to deal with the more complicated, modulated magnetic structures, which will available later, in the fully developed presentation program.

The program can be downloaded in the form of a ZIP archive, including the program, the index and body of the database and two additional modules. All the files should be unpacked into one directory. For the proper work of the program about 560K of free operational memory is required. You can control the program both by mouse and the keyboard. All possible comments and bug descriptions are very welcome. The authors will try to correct the bugs as well as take into account all the users suggestions in the future versions of the program.

New !

You can download the program by clicking HERE (ver.099e) or HERE (ver.099f).

Last updated on: Oct. 01-st, 1998