FeAs-Based Superconductivity: A Case Study of the Effects of Transition Metal Doping on BaFe2As2
The recently discovered FeAs-based superconductors are a new, promising set of materials for technological and basic research. They offer transition temperatures as high as 55 K as well as essentially isotropic, and extremely large, upper, superconducting critical fields, in excess of 40 T at 20 K. In addition, they may well provide insight into exotic superconductivity that extends beyond just FeAs-based superconductivity, perhaps even shedding light on the still-perplexing CuO-based high-Tc materials. Whereas superconductivity can be induced in the RFeAsO (R = rare earth) and AEFe2As2 (AE = Ba, Sr, Ca) families by several means, transition metal (TM) doping of BaFe2As2 [e.g., Ba(Fe1–xTMx)2As2] offers the easiest experimental access to a wide set of materials and states. In this review, we present an overview and summary of the effect of TM-doping (TM = Co, Ni, Cu, Pd, and Rh) on BaFe2As2. The resulting phase diagrams reveal the nature of the interaction between the structural, magnetic, and superconducting phase transitions in these compounds and delineate a region of phase space that allows for the stabilization of superconductivity.