Superconductivity induced by Ni doping inSmFe1−xNixAsO

Abstract

Superconductivity with a Tc of about 10 K is observed in the Ni-dopedSmFe1−xNixAsO system. The measurements of resistivity and magnetic susceptibility show that the spin-density wave(SDW) order is quickly suppressed with increasing Ni content, and superconductivity emerges asx≥0.04.Tcmid shows a maximum of 10.8 Kat x = 0.06, and it drops to lowerthan 2 K as x>0.12. Meanwhile,the upper critical field (Hc2(0)) is estimated to be about 40 T for the optimally-doped sample (x = 0.06). The normal state thermopower is negative for all the Ni-doped samples,indicating that an electron-type charge carrier dominates in the transportproperties. Moreover, the magnitude of the room-temperature thermopowerincreases with increasing Ni content, and then shows a broad peak aroundx = 0.06.We found that there is an obvious correlation between the anomalously enhanced thermopower andsuperconductivity. A phase diagram is derived based on the transport measurements and a dome-likeTc(x) curve is established.