Abstract: The new perovskite cuprate material Sr8CaRe3Cu4O24, which behaves ferrimagnetically and shows an unusually high Curie temperature (Tc=440 K), is found from density\|functional theory calculation to display several surprising properties after hole doping or chemical substitution. Half-metal behavior is realized by replacing Re with W or Mo while Tc remains high. The hole-doped Sr8CaRe3Cu4O24 is also a half-metal with high Tc. Moreover, we find that the O atoms will carry a large magnetic moment after hole doping, which is in sharp contrast to the generally accepted concept that magnetism in solids requires partially filled shells of d or f electrons in cations. The material Sr8CaRe3Cu4O24 is therefore expected to provide a very useful platform for material design and development.