Canted Antiferromagnetism on Rectangular Layers of Fe2+ in Polymorphic CaFeSeO

• Published in: Inorganic chemistry Vol. 56; no. 8; pp. 4271 - 4279
• Main Authors: Lai, Kwing To, Komarek, Alexander Christoph, Fernández-Díaz, Maria Teresa, Chang, Pi-Shan, Huh, Sungjoon, Rosner, Helge, Kuo, Chang-Yang, Hu, Zhiwei, Pi, Tun-Wen, Adler, Peter, Ksenofontov, Vadim, Tjeng, Liu Hao, Valldor, Martin
• Format: Journal Article
• Language: English
• Published: American Chemical Society 17.04.2017
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.6b02098

From stoichiometric amounts of CaO, Fe, and Se, pure powders and single crystals of quaternary Ca [ FeSe 2 / 2 O 2 / 2 ] ∞ 2 can be obtained by solid-state reaction and self-flux growth, respectively. The as-synthesized compound exhibits a polymorphic crystal structure, where the two modifications have different stacking sequences of [ FeSe 2 / 2 O 2 / 2 ] 2 − ∞ 2 layers. The two polymorphs have similar unit cells but different crystal symmetries (Cmc21 and Pnma), of which the former is non-centrosymmetric. Fe is divalent (d6) and high-spin, as proven by X-ray spectroscopy, Mössbauer spectroscopy, and powder neutron diffraction data. The latter two, in combination with magnetic susceptibility and specific heat data, reveal a long-range antiferromagnetic spin order (T N = 160 K) with a minor spin canting. CaFeSeO is an electronic insulator, as confirmed by resistivity measurements and density functional theory calculations. The latter also suggest a relatively small energy difference between the two polymorphs, explaining their intimate intergrowth.