Ferromagnetism in CuFeSb: Evidence of competing magnetic interactions in Fe-based superconductors

In this talk, we will report a new layered iron-pnictide compound CuFeSb [1]. This material shares similar layered tetragonal structure with iron-based superconductors, with Fe square planar sheets forming from the edge-sharing iron antimony tetrahedral network. CuFeSb differs remarkably from Fe-based superconductors in the height of anion Z$_{anion}$ from the Fe plane; Z$_{Sb}$ for CuFeSb is $\sim$1.84 {\AA}, much larger than Z$_{As}$ (1.31-1.51 {\AA}) in FeAs compounds and Z$_{Te}$ ($\sim$1.77 {\AA}) in Fe$_{1+y}$Te. In contrast with the metallic antiferromagneticor superconducting state of iron pnictides and chalcogenides under current studies, CuFeSb exhibits a metallic, ferromagnetic state with $T_{c} =$ 375 K. This finding provide strong experimental evidence for the competition between antiferromagnetic and ferromagneticcorrelations in layered Fe-based superconductors, and that the nature of magnetic coupling within the Fe plane is indeed dependent on the height of anion as predicted in theories [2,3].\\[4pt] [1] B. Qian\textit{ et al.}, Phys. Rev. B \textbf{85}, 144427 (2012).\\[0pt] [2] C.-Y. Moon,\textit{ et a.l}, Phys. Rev. Lett \textbf{104}, 057003 (2010).\\[0pt] [3] W.-G. Yin, \textit{et al.}, Phys. Rev. Lett \textbf{105}, 107004 (2010).