Hydrothermal design of magnetic heterolayer iron-based superconductors

Recently, a new iron-based superconductor, (Li_1-xFe_xOH)FeSe (critical temperature, T_c = 43 K), was reported. Pachmayr et al. and Lu et al. reported observation of ferromagnetism and antiferromagnetism, respectively, in this 43 K superconductor, but no magnetic peak(s) have been observed for this system in several neutron diffraction studies. Thus, our current work aimed at controlling this magnetism through selective doping of other transition metals onto the Li site within the (Li_1-xFe_xOH)^δ+ spacer layers. We have synthesized powder and single crystals (Li_1-x-yFe_xM_yOH)FeSe samples (M = Cr, Mn, Co, Ni, Cu, Zn) through a hydrothermal ion-exchange reaction of KFe_2-2yM_2ySe₂ precursors. These samples have been characterized by x-ray diffraction, electrical resistivity, and magnetic susceptibility to confirm their crystal structure, chemical composition and the influence of transition metal dopants on their superconductivity and magnetism. Neutron diffraction revealed correlation between magnetism and the crystal structure tuned by transition metal dopants in the spacer layers which coexists with superconductivity. Our work demonstrates coexistence of superconductivity and magnetism can be designed through chemical manipulation of heterolayer transition metal chalcogenides.