Room temperature antiferromagnetic order in superconducting X_yFe_{2 −x}Se₂(X = Rb, K): a neutron powder diffraction study

Abstract

Abstract.Magnetic and crystal structures of superconducting X y Fe 2−x Se 2 (X= Rb and K with T c =31.5 K and 29.5 K) have been studied by neutron powder diffraction at room temperature. Both crystals show ordered iron vacancy pattern and the crystal structure is well described in the I4/m space group with the lattice constants a =8.799, c =14.576 and a =8.730, c =14.115Å and the refined stoichiometry x=0.30(1), y=0.83(2) and x=0.34(1), y=0.83(1) for Rb-and K-crystals respectively. The structure contains one fully occupied iron position and one almost empty vacancy position. Assuming that the iron moment is ordered only on the fully occupied site we have sorted out all eight irreducible representations (irreps) for the propagation vector k = 0 and have found that irreps τ 2 and τ 7 well fit the experimental data with the moments along c-axis. The moment amplitudes amounted to 2.15(3) µ B , 2.55(3) µ B for τ 2 and 2.08(6) µ B , 2.57(3) µ B for τ 7 for Rb-and K-crystals respectively. Irrep τ 2 corresponds to the Shubnikov group I4/m and gives a constant moment antiferromagnetic configuration, whereas τ 7 does not have Shubnikov counterpart and allows two different magnetic moments in the structure.

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Vacancy-induced nanoscale phase separation in KxFe2−ySe2Lazarević1, Abeykoon2, Stephens3 et al. 2012Phys. Rev. B487620View full textAdd to dashboardCite

“…The recent discovery of block checkerboard antiferromagnetic order of superconducting materials A x Fe 2−y Se 2 , A = K, Rb, Cs and Tl) has invoked considerable debate in the scientific community. [1][2][3][4][5][6] It was shown that the appearance of antiferromagnetism is a consequence of the Fe vacancy ordering. 7,8 These unique properties among the superconductors opened a question whether Fe vacancies stabilize or destroy the superconductivity.…”