  In this paper we report the comparative study of superconductivity by 3d
(Co), 4d (Rh), 5d (Ir) element doping in SmFeAsO. X-ray diffraction patterns
indicate that the material has formed the ZrCuSiAs-type structure with a space
group P4/nmm. It is found that the antiferromagnetic spin-density-wave (SDW)
order in the parent compounds is rapidly suppressed by Co, Rh, and Ir doping,
and superconductivity emerges. Both electrical resistance and magnetization
measurements show superconductivity up to around 10 K in SmFe1-xMxAsO (M = Co,
Rh, Ir). Co, Rh and Ir locate in the same column in the periodic table of
elements but have different electronic band structure, so comparative study
would add more ingredients to the underlying physics of the iron-based
superconductors.
