scholarly journals Magnetic Option in Jana2006: A Unified Approach by Shubnikov (Super)space Groups

2014 ◽  
Vol 70 (a1) ◽  
pp. C520-C520
Author(s):  
Vaclav Petricek ◽  
Michal Dusek
Keyword(s):  
Parent Phase ◽  
Magnetic Scattering ◽  
Unified Approach ◽  
Space Groups ◽  
Magnetic Structures ◽  
Structure Factors ◽  
Generalized Symmetry ◽  
Magnetic Symmetry ◽  
Two Phases ◽  
Unified Description

The concept of Shubnikov (magnetic) symmetry becomes frequently used for description, solution and refinement of magnetic structures. Its growing importance is connected with the ease of application to various classes of magnetic structures having the translation periodicity identical, commensurate or incommensurate with the nuclear one. Recently generalized superspace approach [1] for incommensurately modulated magnetic structures allows for combination of nuclear and magnetic modulations. This unified description helps fully understand e.g. multiferroic phases. The program Jana2006 (http://jana.fzu.cz) combines the concept of Shubnikov (super)space groups with the representational analysis based on the decomposition of the magnetic configuration space into basis modes, which transform according to different physically irreducible representations (irreps) of the space group of the paramagnetic phase [2]. Moreover, Jana2006 can launch the recently developed program ISODISTORT [3] to obtain similar but more general analysis. The generalized symmetry concept facilitates data processing where symmetry related reflections for single crystal data can be merged and the list of generated reflections for powder data can be reduced to independent ones. Another benefit concerns calculation of magnetic structure factors, stability of refinement and logical way to describe twin domains. Unlike in the Fullproff program [6], Jana2006 can combine the nuclear and magnetic scattering internally without necessity to introduce two phases. It can also calculate magnetic structures with modulated parent phase where the modulation appears before the magnetic phase transition. The lecture shows manifold possibilities how to refine modulated magnetic structures from various experiments. Several recently solved magnetic structures will be presented.

scholarly journals A historical introduction to the symmetries of magnetic structures. Part 1. Early quantum theory, neutron powder diffraction and the coloured space groups

2017 ◽  
Vol 32 (2) ◽  
pp. 148-155 ◽  
Author(s):  
Andrew S. Wills
Keyword(s):  
Time Reversal ◽  
Magnetic Ordering ◽  
Neutron Powder Diffraction ◽  
Quantum Mechanical ◽  
Langevin Model ◽  
Space Groups ◽  
Magnetic Structures ◽  
Black And White ◽  
Magnetic Symmetry ◽  
Looking Back

This paper introduces the historical development of the symmetries for describing magnetic structures culminating in the derivation of the black and white and coloured space groups. Beginning from the Langevin model of the Curie law, it aims to show the challenges that magnetic ordering presented and how different symmetry frameworks were developed to meet them. As well as explaining core ideas, later papers will show how the different schemes are connected. With these goals in mind, the maths related is kept to the minimum required for clarity. Those wishing to learn more details are invited to engage with the references. As well as looking back and reviewing the development of magnetic symmetry over time, particular attention is spent on explaining where the concept of time-reversal has been applied. That time-reversal has different meaning in classical and quantum mechanical situations, has created confusions which continue to propagate.

scholarly journals A collection of magnetic structures with cif-like files as a database seed

2014 ◽  
Vol 70 (a1) ◽  
pp. C1369-C1369
Author(s):  
Samuel Gallego ◽  
J. Manuel Perez-Mato ◽  
Emre Tasci ◽  
Luis Elcoro ◽  
Mois Aroyo ◽  
...  
Keyword(s):  
Magnetic Moments ◽  
Parent Phase ◽  
Point Group ◽  
Original Data ◽  
Quantitative Information ◽  
Isotropy Subgroup ◽  
Magnetic Structures ◽  
Structure Description ◽  
Magnetic Symmetry ◽  
The Cost

We report the release within the Bilbao Crystallographic server [1] of a webpage providing detailed quantitative information on a representative set of published magnetic structures. Under the name of MAGNDATA (www.cryst.ehu.es/magndata) more than 140 entries are available. Each magnetic structure has been saved making use of magnetic symmetry, i.e. Shubnikov magnetic groups for commensurate structures, and magnetic superspace groups for incommensurate ones. This ensures a unified communication method and a robust and unambiguous description of both atomic positions and magnetic moments. The origin and main crystallographic axes of the parent phase are usually kept, with the cost of often using a non-standard setting for the magnetic symmetry. The magnetic point group is also given, so that the allowed macroscopic tensor properties can be derived. The fact that magnetic structures are being described according to various methods, often with ambiguous information, has forced an elaborate interpretation and transformation of the original data. For this purpose the freely available internet tools MAXMAGN [1] and ISODISTORT [2] have been our essential tools. Most of the analyzed structures happen to possess maximal magnetic symmetries within the constraints imposed by the magnetic propagation vector, and the relevant model could be derived in a straightforward manner using MAXMAGN [1]. In a few cases a lower symmetry is realized, but then it corresponded to one isotropy subgroup of one or several irreducible representations (irreps) of the paramagnetic grey space group, and ISODISTORT [2] could be applied to model the structure. Although the structure description is done using magnetic groups, the active irrep(s) are also given in most cases. The entries of the collection can be retrieved in a cif-like format, which is supported by internet tools as STRCONVERT [1] and ISOCIF [2], the visualization program VESTA [3], and some refinement programs (JANA2006, FULLPROF). Each entry also includes Vesta files that allow the visualization of a single magnetic unit cell.

MAGNDATA: towards a database of magnetic structures. I. The commensurate case

2016 ◽  
Vol 49 (5) ◽  
pp. 1750-1776 ◽  
Author(s):  
Samuel V. Gallego ◽  
J. Manuel Perez-Mato ◽  
Luis Elcoro ◽  
Emre S. Tasci ◽  
Robert M. Hanson ◽  
...  
Keyword(s):  
Magnetic Moments ◽  
Parent Phase ◽  
Point Group ◽  
Quantitative Information ◽  
Isotropy Subgroup ◽  
Published Data ◽  
Cell Orientation ◽  
Space Group ◽  
Magnetic Structures ◽  
Magnetic Symmetry

A free web page under the name MAGNDATA, which provides detailed quantitative information on more than 400 published magnetic structures, has been developed and is available at the Bilbao Crystallographic Server (http://www.cryst.ehu.es). It includes both commensurate and incommensurate structures. This first article is devoted to explaining the information available on commensurate magnetic structures. Each magnetic structure is described using magnetic symmetry, i.e. a magnetic space group (or Shubnikov group). This ensures a robust and unambiguous description of both atomic positions and magnetic moments within a common unique formalism. A non-standard setting of the magnetic space group is often used in order to keep the origin and unit-cell orientation of the paramagnetic phase, but a description in any desired setting is possible. Domain-related equivalent structures can also be downloaded. For each structure its magnetic point group is given, and the resulting constraints on any macroscopic tensor property of interest can be consulted. Any entry can be retrieved as a magCIF file, a file format under development by the International Union of Crystallography. An online visualization tool using Jmol is available, and the latest versions of VESTA and Jmol support the magCIF format, such that these programs can be used locally for visualization and analysis of any of the entries in the collection. The fact that magnetic structures are often reported without identifying their symmetry and/or with ambiguous information has in many cases forced a reinterpretation and transformation of the published data. Most of the structures in the collection possess a maximal magnetic symmetry within the constraints imposed by the magnetic propagation vector(s). When a lower symmetry is realized, it usually corresponds to an epikernel (isotropy subgroup) of one irreducible representation of the space group of the parent phase. Various examples of the structures present in this collection are discussed.

Magnetic symmetry in the Bilbao Crystallographic Server: a computer program to provide systematic absences of magnetic neutron diffraction

2012 ◽  
Vol 45 (6) ◽  
pp. 1236-1247 ◽  
Author(s):  
Samuel V. Gallego ◽  
Emre S. Tasci ◽  
Gemma de la Flor ◽  
J. Manuel Perez-Mato ◽  
Mois I. Aroyo
Keyword(s):  
Neutron Diffraction ◽  
Computer Program ◽  
Magnetic Moments ◽  
General Information ◽  
Resolving Power ◽  
Space Groups ◽  
Magnetic Structures ◽  
Starting Point ◽  
Magnetic Symmetry ◽  
Symmetry Operations

MAGNEXTis a new computer program available from the Bilbao Crystallographic Server (http://www.cryst.ehu.es) that provides symmetry-forced systematic absences or extinction rules of magnetic nonpolarized neutron diffraction. For any chosen Shubnikov magnetic space group, the program lists all systematic absences, and it can also be used to obtain the list of the magnetic space groups compatible with a particular set of observed systematic absences. Absences corresponding to specific ordering modes can be derived by introducing effective symmetry operations associated with them. Although systematic extinctions in neutron diffraction do not possess the strong symmetry-resolving power of those in nonmagnetic crystallography, they can be important for the determination of some magnetic structures. In addition,MAGNEXTprovides the symmetry-adapted form of the magnetic structure factor for different types of diffraction vectors, which can then be used to predict additional extinctions caused by some prevailing orientation of the atomic magnetic moments. This program, together with a database containing comprehensive general information on the symmetry operations and the Wyckoff positions of the 1651 magnetic space groups, is the starting point of a new section in the Bilbao Crystallographic Server devoted to magnetic symmetry and its applications.

scholarly journals A complicated quasicrystal approximant ∊16 predicted by the strong-reflections approach

2010 ◽  
Vol 66 (1) ◽  
pp. 17-26 ◽  
Author(s):  
Mingrun Li ◽  
Junliang Sun ◽  
Peter Oleynikov ◽  
Sven Hovmöller ◽  
Xiaodong Zou ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Unit Cell ◽  
Space Groups ◽  
Inverse Fourier Transformation ◽  
Transmission Electron ◽  
Structure Factors ◽  
Precession Electron Diffraction ◽  
Density Map ◽  
Electron Density Map ◽  
Good Agreement

The structure of a complicated quasicrystal approximant ∊16 was predicted from a known and related quasicrystal approximant ∊6 by the strong-reflections approach. Electron-diffraction studies show that in reciprocal space, the positions of the strongest reflections and their intensity distributions are similar for both approximants. By applying the strong-reflections approach, the structure factors of ∊16 were deduced from those of the known ∊6 structure. Owing to the different space groups of the two structures, a shift of the phase origin had to be applied in order to obtain the phases of ∊16. An electron-density map of ∊16 was calculated by inverse Fourier transformation of the structure factors of the 256 strongest reflections. Similar to that of ∊6, the predicted structure of ∊16 contains eight layers in each unit cell, stacked along the b axis. Along the b axis, ∊16 is built by banana-shaped tiles and pentagonal tiles; this structure is confirmed by high-resolution transmission electron microscopy (HRTEM). The simulated precession electron-diffraction (PED) patterns from the structure model are in good agreement with the experimental ones. ∊16 with 153 unique atoms in the unit cell is the most complicated approximant structure ever solved or predicted.

Neutrons Not Entitled to Retire at the Age of 60: More than Ever Needed to Reveal Magnetic Structures

2011 ◽  
Vol 170 ◽  
pp. 263-269 ◽  
Author(s):  
Clemens Ritter
Keyword(s):  
Rare Earth ◽  
Giant Magnetoresistance ◽  
High Temperature Superconductivity ◽  
Functional Materials ◽  
Symmetry Analysis ◽  
Magnetic Shape Memory ◽  
Magnetic Structures ◽  
Magnetic Symmetry ◽  
The Rare Earth

In 1949 Shull et al. [1] used for the first time neutrons for the determination of a magnetic structure. Ever since, the need for neutrons for the study of magnetism has increased. Two main reasons can be brought forward to explain this ongoing success: First of all a strong rise in research on functional materials (founding obliges) and secondly the increasing availability of easy to use programmes for the treatment of magnetic neutron diffraction data. The giant magnetoresistance effect, multiferroic materials, magnetoelasticity, magnetic shape memory alloys, magnetocaloric materials, high temperature superconductivity or spin polarized half metals: The last 15 years have seen the event of all these “hot topics” where the knowledge of the magnetism is a prerequisite for understanding the underlying functional mechanisms. Refinement programs like FULLPROF or GSAS and programs for magnetic symmetry analysis like BASIREPS or SARAH make the determination of magnetic structures accessible for non specialists. Following a historical overview on the use of neutron powder diffraction for the determination of magnetic structures, I will try to convince you of the easiness of using magnetic symmetry analysis for the determination of magnetic structures using some recent examples of own research on the rare earth iron borate TbFe3(BO3)4 and the rare earth transition metal telluride Ho6FeTe2.

scholarly journals Double antisymmetry in magnetic structures

2014 ◽  
Vol 70 (a1) ◽  
pp. C518-C518
Author(s):  
Brian VanLeeuwen ◽  
Mantao Huang ◽  
Daniel Litvin ◽  
Venkatraman Gopalan
Keyword(s):  
Magnetic Structure ◽  
Structure Determination ◽  
Time Reversal ◽  
Time Reversal Symmetry ◽  
Space Group ◽  
Space Groups ◽  
Magnetic Structures ◽  
Recent Introduction ◽  
Symmetry Constraints

This work follows from the recent introduction of the rotation-reversal operation intended to be analogous to the time-reversal operation used to describe the symmetry of magnetic structures. As a second independent antisymmetry operation, this operation "doubles" the antisymmetry of the magnetic space groups, hence the term double antisymmetry. Supposing the consideration of both rotation-reversal and time-reversal symmetry, it was found that there are 17,803 types of symmetry that a crystal could exhibit; the 1,651 magnetic space group types being a subset of these, just as the 230 crystallographic space group types are a subset of the magnetic space group types. In addition to discussing the methods applied to determine these types, describing their properties, and listing their symmetry diagrams (available online), the implications for symmetry constraints in magnetic structure determination will be explored.

Neutron Studies of the Iron-based Family of High Tc Magnetic Superconductors

2008 ◽  
Vol 1148 ◽  
Author(s):  
Jeffrey W. Lynn
Keyword(s):  
Magnetic Order ◽  
Spin Dynamics ◽  
Magnetic Scattering ◽  
Anisotropic Pressure ◽  
Itinerant Electron ◽  
Superconducting Transition ◽  
Orthogonal Direction ◽  
Magnetic Structures ◽  
Se Doping ◽  
Iron Based

AbstractWe briefly review recent neutron scattering investigations carried out at the NIST Center for Neutron Research on the crystal structures, magnetic structures, and spin dynamics of the iron-based ROFe(As,P) (R=La, Ce, Pr, Nd), and (Ba,Sr,Ca)Fe2As2 systems. All the undoped materials exhibit universal behavior, where a tetragonal-to-orthorhombic structural transition occurs between ˜100−220 K, below which the systems become antiferromagnets. The magnetic structure within the a-b plane consists of chains of parallel Fe spins that are coupled antiferromagnetically in the orthogonal direction, with an ordered moment typically less than one Bohr magneton. Hence these are itinerant electron magnets, with a spin structure that is consistent with Fermi-surface nesting and a spin wave bandwidth ˜200 meV. The rare-earth moments order antiferromagnetically at low T like ‘conventional’ magnetic-superconductors. With doping, the structural and magnetic transitions are suppressed in favor of superconductivity, with superconducting transition temperatures up to 56 K, while the Ce crystal field linewidths are affected when superconductivity sets in. The application of pressure in CaFe2As2 transforms the system from a magnetically ordered orthorhombic material to a ‘collapsed’ non-magnetic tetragonal system which is superconducting at lower T when anisotropic pressure is applied. Fe1+xTe shows a transition from a monoclinic to orthorhombic low T structure with increasing x, and a crossover from commensurate to incommensurate magnetic order. Se doping suppresses the magnetic order, while incommensurate magnetic scattering is observed in the superconducting regime.

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