We report on the study of some new derivatives of the complex perovskite CaCu3Mn4O12. Ca2+ cations can be replaced by rare earths in the RCu3Mn4O12 (R = rare earths) family, implying an electron doping effect that dramatically affects the magnetic properties. These compounds must be prepared under high pressure conditions. We have synthesized for the first time, at 2 GPa in a piston-cylinder press, some new members of the family, with R = Pr, Sm, Eu, Gd, Dy, Ho, Tm and Yb, for which we describe structural and magnetization data. The materials with non-absorbing rare earths have been studied by means of neutron powder diffraction, allowing us to determine the subtle structural features which are related to the observed physical properties. In fact, for most of the R cations, the ferromagnetic T-C increases remarkably up to 400 K.