  The vanadium doping effects on superconductivity and magnetism of iron
pnictides are investigated in Ba(Fe$_{0.92-x}$Co$_{0.08}$V$_x$)$_2$As$_2$ by
transport, susceptibility and neutron scattering measurements. The doping of
magnetic impurity V causes a fast suppression of superconductivity with T$_c$
reduced at a rate of 7.4~K/1\%V. On the other hand, the long-range commensurate
$C$-type antiferromagnetic order is recovered upon the V doping. The value of
ordered magnetic moments of Ba(Fe$_{0.92-x}$Co$_{0.08}$V$_x$)$_2$As$_2$ follows
a dome-like evolution versus doping concentration x. A possible Griffiths-type
antiferromagnetic region of multiple coexisting phases in the phase diagram of
Ba(Fe$_{0.92-x}$Co$_{0.08}$V$_x$)$_2$As$_2$ is identified, in accordance with
previous theoretical predictions based on a cooperative behavior of the
magnetic impurities and the conduction electrons mediating the
Ruderman-Kittel-Kasuya-Yosida interactions between them.
