  A new metallic radical cation salt
$\kappa$-(BETS)$_2$Co$_{0.13}$Mn$_{0.87}$[N(CN)$_2$]$_3$, where BETS is
bis(ethylenedithio)tetraselenafulvalene, C$_{10}$S$_4$Se$_4$H$_8$, has been
synthesized. In this salt, a part of Mn$^{2+}$ ions are replaced by Co$^{2+}$
which acts as a magnetic dopant with a different effective magnetic moment.
Crystal structure, band structure, conducting and magnetic properties of the
salt have been studied. Below 30 K the material undergoes a metal-insulator
transition, which is suppressed by applying a pressure of ~0.5kbar, leading to
a superconducting ground state. While the structural and conducting properties
are very similar to those of the parent salt
$\kappa$-(BETS)$_2$Mn[N(CN)$_2$]$_3$, magnetic properties associated with
localized moments in the anion layer are found to be surprisingly different.
