Common crystalline and magnetic structure of superconducting A₂Fe₄Se₅ (A=K,Rb,Cs,Tl) single crystals measured using neutron diffraction

Single-crystal neutron diffraction studies on superconductors A₂Fe₄Se₅ , where A=Rb, Cs, (Tl, Rb), and (Tl, K) (T_c ∼30K), uncover the same Fe vacancy ordered crystal structure and the same block antiferromagnetic order as in K₂Fe₄Se₅ . The Fe order-disorder transition occurs at T_S =500-578K, and the antiferromagnetic transition at T_N =471-559K with an ordered magnetic moment ∼3.3μ_B / Fe at 10 K. Thus, all recently discovered A intercalated iron selenide superconductors share the common crystalline and magnetic structure, which are very different from previous families of Fe-based superconductors, and constitute a distinct new 245 family.