Doping effect of Cu and Ni impurities on the Fe-based superconductor Ba0.6K0.4Fe2As2 Peng Cheng, Bing Shen, Fei Han and Hai-Hu Wen EPL, 104 3 (2013) 37007 Published online: 04 December 2013 DOI: 10.1209/0295-5075/104/37007