CO-doping effects on the transport and magnetic properties of FeTe

Here we report a systematic investigation of Co-doping effects on the magnetism and transport properties of Fe1+yTe single crystals. It is found that the anti-ferromagnetism transition temperature decreases upon Co doping, and a spin-glass like behavior emerges at low temperature. With substituting more than x=0.09 Co for Fe, both the metallic behavior and the structural transition disappear, but the density of states at Fermi-level does not change significantly. These results suggest that Co doping does not act as carrier doping but is more likely to bring in random magnetic scatters. In addition, the analysis of RH measurements reveals that the Fermi-level reconstruction is not closely related to the long rang AFM transition, which further supports for the local moment picture with frustrated character in dominating the AFM ground state of Fe1+yTe.