  The effects of $n$-type carrier doping by Li intercalation on magnetism in
undoped and Co-doped anatase TiO$_2$ are investigated. We have found that doped
$n$-type carriers in TiO$_2$ are localized mainly at Ti sites near the
intercalated Li. With increasing the intercalation, local spins are realized at
Ti. In the case of Co-doped TiO$_2$, most of the added $n$-type carriers fill
the Co 3$d$ bands and the rest are localized at Ti. Therefore, Co magnetic
moment vanishes by Li intercalation to have a nonmagnetic ground state.
