Temperature and composition phase diagram in the iron-based ladder compounds Ba1-xCsxFe2Se3

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We investigated the iron-based ladder compounds (Ba,Cs)Fe₂Se₃. Their parent compounds, BaFe₂Se₃ and CsFe₂Se₃, have different space groups, formal valences of Fe and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, X-ray diffraction and powder neutron diffraction measurements were conducted to obtain temperature and composition phase diagram of this system. Block magnetism observed in BaFe₂Se₃ is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe₂Se₃ is not so fragile against Ba doping. New type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe₂Se₃, but inter-ladder spin configuration is different. Intermediate compounds show insulating behavior, nevertheless finite T-linear contribution in specific heat was obtained at low temperatures.