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Lack of a threefold rotation axis in α‐Fe 2 O 3 and α‐Cr 2 O 3 crystals
Author(s) -
Stękiel Michał,
Przeniosło Radosław,
Sosnowska Izabela,
Fitch Andrew,
Jasiński Jacek B.,
Lussier Joey A.,
Bieringer Mario
Publication year - 2015
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s205252061500342x
Subject(s) - crystallography , monoclinic crystal system , crystal structure , space group , trigonal crystal system , rotation (mathematics) , bar (unit) , group (periodic table) , space (punctuation) , crystal (programming language) , symmetry (geometry) , materials science , condensed matter physics , chemistry , physics , x ray crystallography , diffraction , geometry , optics , mathematics , meteorology , computer science , linguistics , organic chemistry , philosophy , programming language
The crystal structure of α‐Fe 2 O 3 and α‐Cr 2 O 3 is usually described with the corundum‐type trigonal crystal structure based on the space group . There are, however, some observations of the magnetic ordering of both α‐Fe 2 O 3 and α‐Cr 2 O 3 that are incompatible with the trigonal symmetry. We show experimental evidence based on X‐ray powder diffraction and supported by transmission electron microscopy that the symmetry of the crystal structure of both α‐Fe 2 O 3 and α‐Cr 2 O 3 is monoclinic and it is described with the space group C 2/ c (derived from by removing the threefold rotation axis). The magnetic orderings of α‐Fe 2 O 3 and α‐Cr 2 O 3 are compatible with the magnetic space groups C 2/ c and C 2/ c ′, respectively. These findings are in agreement with the idea from Curie [(1894), J. Phys. 3 , 393–415] that the dissymmetry of the magnetic ordering should be associated with a dissymmetry of the crystal structure.