Abstract
We report Zn-doping effect in the parent and F-doped LaFeAsO oxy-arsenides. Slight Zn doping in LaFe1- xZnxAsO 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 Tc of LaFe1-xZnxAsO0.9F0.1, in contrast to the effect of Zn doping in high-Tc 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.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. Through the various doping approaches, it is widely believed that high-Tc superconductivity appears from the suppression of spin-density wave type antiferromagnetic (AFM) order in iron arsenides. In contrast to high-Tc cuprates, superconductivity can be induced even by doping Co or Ni in Fe sites, or P doping in As sites. The competition of AFM and superconducting orders implies that the superconducting paring mechanism might have a magnetic origin.
Main results. In Zn doped parent compound LaFeAsO, the addition of Zn was found to suppress the AFM transition and to turn the system into a semiconductor-like phase instead of superconducting phase. While in the superconducting LaFeAsO0.9F0.1, Zn doping almost has no influence on the superconductivity. It is clear that Zn doping selectively destroys the AFM transition but without resulting in a superconducting phase. Nevertheless Zn doping does not severely disturb the existing superconducting state although it does not create one.
Wider implications. This is a surprising example in which a mechanism that suppresses the AFM order does not instigate superconductivity. This will be very important for the further development of theoretical models behind both superconducting and AFM transitions in these interesting compounds.