Canted Antiferromagnetism on Rectangular Layers of Fe²⁺ in Polymorphic CaFeSeO

Abstract

From stoichiometric amounts of CaO, Fe, and Se, pure powders and single crystals of quaternary [Formula: see text] 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 [Formula: see text] layers. The two polymorphs have similar unit cells but different crystal symmetries (Cmc2 and Pnma), of which the former is non-centrosymmetric. Fe is divalent (d) 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 = 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.

Successive Phase Transitions in Fe2+ Ladder Compounds Sr2Fe3Ch2O3 (Ch = S, Se)

“…XAS at the 3d transition metal (TM) L 2,3 edges is a very sensitive technique to establish their valence states, spin states, and local symmetries in the solid state matter. − Figure shows that the Fe-L 2,3 XAS spectrum of (a) Sr 2 Fe 3 S 2 O 3 has its main weight at the same energy position as that of an Fe 2+ reference (b) CaFeSeO and (c) Mg 0.94 Fe 0.04 O, but is shifted by 1.6 eV to lower energies with respect to Fe 3+ reference (d) α-Fe 2 O 3 . This confirms an Fe 2+ valence state of Sr 2 Fe 3 S 2 O 3 , agreeing with the expectations from the chemical compositions.…”

Function of Tetrahedral ZnS3O Building Blocks in the Formation of SrZn2S2O: A Phase Matchable Polar Oxysulfide with a Large Second Harmonic Generation Response

“…These close packed layers are stacked parallel with A 2+ layers perpendicular to the hexagonal c -axis, unlike SrZn 2 S 2 O, where the layers are parallel to the hexagonal c -axis. Another example is CaFeSeO, crystallizing in the space group Cmc 2 1 , , which can be considered to be a member of a homologous series (AO)­(MQ) n (M = Fe, Zn; n = 1, 2) to which CaFeSeO and SrZn 2 S 2 O belong. CaFeSeO contains puckered sheets consisting of FeSe 2 O 2 tetrahedra located in the ac plane that are also vertically separated by Ca 2+ layers oriented parallel to the hexagonal c axis.…”

“…One of the most useful elements for optical applications is Zn 2+ with a d 10 electron configuration, where for oxychalcogenides, large band gap, optically transparent, polar materials have been reported, including BaZnSO, SrZnSO, and CaZnSO . These compositions are related to several iron and cobalt oxychalcogenide phases, CaFeSO, CaCoSO, and CaFeSeO. ,, The symmetries and tilts of these compositions are quite varied and result in different space groups, for example, BaZnSO ( Cmcm ), SrZnSO ( P 6 3 mc ), CaFeSO ( P 6 3 mc ), CaZnSO ( P 6 3 mc ), CaFeSeO ( Cmc 2 1 ), and CaFeSeO ( Pmcn ); furthermore, multiple polymorphs can crystallize together.…”

Synthesis, Crystal Structure, and Physical Properties of Layered LnCrSe2O (Ln = Ce–Nd)

“…To date, researchers are interested in the oxychalcogenides based on late transition metals (Fe, Co, Cu, Ag, Zn, Cd) for their abundant physical properties and potential applications. Taking Fe as an example, the reported Fe-based oxychalcogenides include the superconducting [Li 0.8 ­Fe 0.2 OH]­[Fe Q ] ( Q = S, Se), − the semiconductive CaFe Q O ( Q = S, Se), − the antiferromagnetic Ln 2 Fe 2 Q 2 O 3 ( Ln = La, Ce; Q = S, Se), and Sr 2 Fe 3 ­Se 2 O 3 with much complex magnetic ordering. , Even though the oxychalcogenides in the Ln / M /Q/O ( Ln = rare earth metal, M = early transition metals) family have also been explored, researches on their physical properties remain far to be desired. − Hence, more work should focus on the early transition metal oxychalcogenides as well as their physical properties.…”