  The new perovskite cuprate material Sr$_{8}$CaRe$_{3}$Cu$_{4}$O$_{24}$, which
behaves ferrimagnetically and shows an unusually high Curie temperature ($T_c
\sim$ 440 K), is found from density-functional theory calculation to display
several surprising properties after hole doping or chemical substitution: (1)
Half metal (HM) is realized by replacing Re with W or Mo while $T_c$ remains
high; (2) hole-doped Sr$_{8}$CaRe$_{3}$Cu$_{4}$O$_{24}$ is also HM with high
$T_c$. Moreover, we find that the O atoms will carry a large magnetic moment
after hole doping, which is in sharp contrast with the generally accepted
concept that magnetism in solid requires partially filled shells of $d$ or $f$
electrons in cations. The material Sr$_8$CaRe$_3$Cu$_4$O$_{24}$ is therefore
expected to provide a very useful platform for material design and development.
