Effect of Zn doping on magnetic order and superconductivity in LaFeAsO

Abstract

We report Zn-doping effect in the parent and F-doped LaFeAsO oxy-arsenides. Slight Zn doping in LaFe_{1- x}Zn_xAsO drastically suppresses the resistivity anomaly around 150 K associated with the antiferromagnetic (AFM) spin density wave (SDW) in the parent compound. The measurements of magnetic susceptibility and thermopower confirm further the effect of Zn doping on AFM order. Meanwhile Zn doping does not affect or even enhances the T_c of LaFe_1-xZn_xAsO_0.9F_0.1, in contrast to the effect of Zn doping in high-T_c cuprates. We found that the solubility of Zn content (x) is limited to less than 0.1 in both systems and further Zn doping (i.e. x ≥0.1) causes phase separation. Our study clearly indicates that the non-magnetic impurity of Zn²⁺ ions doped in the Fe₂As₂ layers affects selectively the AFM order and superconductivity remains robust against the Zn doping in the F-doped superconductors.