Doping effects of Sb in FeTe_1-xSb_x single crystals

We investigated the doping effects of Sb on the magnetic, transport and structural properties in FeTe_1-xSb_x single crystals. Resistivity, magnetic susceptibility and heat capacity experiments consistently reveal that the magnetic/structural transition temperature T_N ~ 70 K in undoped Fe_1.05Te is gradually suppressed by Sb doping, but no superconductivity is observed for x up to 10%. It is found that the electronic heat capacity coefficient gamma increases with Sb content, implying the increase of the density of states at Fermi level. Referring to previous calculation reports, this means that the Sb substituent plays a role of hole carrier doping, which is consistent with our measurements on Hall coefficient. Structural Analysis shows that Sb doping induces an expansion of the lattice along the a axis and a shrinkage along the c axis. Our work suggests that the antiferromagnetism in Fe_1+yTe may be different in nature with other parent compounds of FeAs-based systems.