  In this work, we report the simulation of C4+ irradiation and its significant
effects towards the enhancement of the critical current density in
BaFe1.9Ni0.1As2 single crystals. BaFe1.9Ni0.1As2 single crystals with and
without the C-implantation were characterized by magneto-transport and magnetic
measurements up to 13 T over a wide range of temperatures below and above the
superconducting critical temperature, Tc. It is found that the C-implantation
causes little change in Tc, but it can greatly enhance the in-field critical
current density by a factor of up to 1.5 with enhanced flux jumping at 2 K. Our
Monte Carlo simulation results show that all the C ions end up in a well
defined layer, causing extended defects and vacancies at the layer, but few
defects elsewhere on the implantation paths. This type of defect distribution
is distinct from the columnar defects produced by heavy ion implantation.
Furthermore, the normal state resistivity is enhanced by the light C4+
irradiation, while the upper critical field, Hc2, the irreversibility field,
Hirr, and Tc were affected very little.
