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Crystallite size effect on the monoclinic deformation of the bcc crystal structure of chromium

DOI: 10.1016/j.physb.2017.10.086 DOI Help

Authors: R. Przeniosło (University of Warsaw) , P. Fabrykiewicz (University of Warsaw) , I. Sosnowska (University of Warsaw) , D. Wardecki (University of Warsaw) , W. A. Slawinski (ISIS Facility) , H. Y. Playford (ISIS Facility) , R. Hempelmann (University of Saarland) , M. Bukowski (University of Saarland)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physica B: Condensed Matter

State: Published (Approved)
Published: October 2017
Diamond Proposal Number(s): 16499

Abstract: The modulated spin density wave magnetic orderings observed in chromium suggests that the crystal structure of chromium cannot be described by the cubic space group Im3¯m . Our experimental studies of polycrystalline and nanocrystalline chromium by synchrotron radiation (SR) and neutron powder diffraction show a hkl-dependent Bragg peak broadening which can be interpreted by the low-symmetry monoclinic space group P21/n instead of the high symmetry cubic space group Im3¯m . The monoclinic angle is βm = 90.05 (1)° and 90.29 (1)° for for polycrystalline Cr and nanocrystalline Cr, respectively. The relative monoclinic distortion observed in chromium is 5 times larger than those reported for several oxides: BiFeO3 , α−Fe2O3 , Cr2O3 and calcite. The symmetry of the magnetic transverse spin density wave (TSDW) and the longitudinal spin density wave (LSDW) observed in Cr are described by using the superspace groups P21/n(0β0)00 and P21′/n′(0β0)00 , respectively. These superspace groups describe both the magnetic modulations and the atomic position modulations reported in the literature. The monoclinic symmetry of chromium is a robust effect which is observed in the paramagnetic as well as in the TSDW and LSDW phases.

Journal Keywords: Chromium; Antiferromagnetism; Spin density wave; Symmetry; Superspace groups; X-ray and neutron diffraction

Diamond Keywords: Antiferromagnetism

Subject Areas: Physics, Materials

Instruments: I15-1-X-ray Pair Distribution Function (XPDF)

Other Facilities: ID-31 at ESRF

Added On: 31/10/2017 14:38

Discipline Tags:

Quantum Materials Physics Hard condensed matter - structures Magnetism Materials Science

Technical Tags:

Diffraction Scattering X-ray Powder Diffraction Pair Distribution Function (PDF)