  We report synthesis, structural details and magnetization of SmFe1-xCoxAsO
with x ranging from 0.0 to 0.30. It is found that Co substitutes fully at Fe
site in SmFeAsO in an iso-structural lattice with slightly compressed cell. The
parent compound exhibited known spin density wave (SDW) character below at
around 140 K. Successive doping of Co at Fe site suppressed the SDW transition
for x = 0.05 and later induced superconductivity for x = 0.10, 0.15 and 0.20
respectively at 14, 15.5 and 9K. The lower critical field as seen from
magnetization measurements is below 200Oe. The appearance of bulk
superconductivity is established by wide open isothermal magnetization M(H)
loops. Superconductivity is not observed for higher content of Co i.e. x =
0.30. Clearly the Co substitution at Fe site in SmFe1-xCoxAsO diminishes the Fe
SDW character, introduces bulk superconductivity for x between 0.10 and 0.20
and finally becomes non-superconducting for x above 0.20. The Fe2+ site Co3+
substitution injects mobile electrons to the system and superconductivity
appears, however direct substitution introduces simultaneous disorder in
superconducting FeAs layer and thus superconductivity disappears for higher
content of Co.
