Suppressed Antiferromagnetism and Superconductivity in As-deficient Iron-based Superconductor of SrFe1.8Co0.2Asx

Iron-based superconductors namely Sr(Fe1.8Co0.2)As-1.8 (FeAs1.8) and Sr(Fe1.8Co0.2)As-1.85 (FeAs1.85) with As deficiency are prepared by solid-state reaction. X-ray diffraction reveals that the polycrystalline phase forms in the studied samples, identical to typical SrFe2As2 (122) matrix. Resistive and magnetic measurements show that the superconducting transition temperatures (T-c) are about 19 K for both FeAs1.8 and FeAs1.85. Compared with the performances of typical iron-based 122 superconductors arising from Co doping, the present samples show the suppressed superconductivity. Moreover, the antiferromagnetic (AFM) phase correlated with spin-density-wave (SDW) is reduced as well. The AFM transition temperature decreases to 122 K for FeAs1.85, while such a phase transition is absent at all for FeAs1.8, one sample with less As, implying that the existence of SDW and antiferromagnetism is more sensitive to As content.