  The discovery of novel structural and physical properties in the $A$-site
ordered manganite $R$BaMn$_2$O$_6$ ($R$ = Y and rare earth elements) has
demanded new comprehension about perovskite manganese oxides. In the present
study, the $A$-site disordered form $R$$_{0.5}$Ba$_{0.5}$MnO$_3$ was
successfully synthesized and compared with $R$BaMn$_2$O$_6$ in the structures
and electromagnetic properties. $R$$_{0.5}$Ba$_{0.5}$MnO$_3$ has a primitive
cubic perovskite cell. Unexpectedly the magnetic glassy states are dominant as
the ground state for $R$$_{0.5}$Ba$_{0.5}$MnO$_3$. A peculiar behavior, the
steplike ultrasharp magnetization and resistivity change, has been observed in
Pr$_{0.5}$Ba$_{0.5}$MnO$_3$.
