  We have investigated electron- and hole-doping effects on $A$-site ordered
perovskite manganite NdBaMn$_2$O$_6$, which has the $A$-type (layered)
antiferromagnetic (AFM) ground state. Electrons (holes) are introduced by
partial substitution of Ba$^{2+}$ (Nd$^{3+}$) with Nd$^{3+}$ (Ba$^{2+}$).
Electron-doping generates ferromagnetic (FM) clusters in the $A$-type AFM
matrix. With increasing the electron-doping level, the volume fraction of the
FM phase or the number of the FM clusters is abruptly increasing. In contrast,
the $A$-type AFM phase is robust against the hole-doping, and no FM correlation
is observed in the hole-doped NdBaMn$_2$O$_6$.
