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High oxygen pressure techniques were used to prepare two ferromagnetic compounds of the series La(Cu3-xMnx)Mn4O12 (x=1 and x=2). In a previous work, the end member LaCu3Mn4O12 was reported to be cubic, space group Im3, showing a ferrimagnetic structure driven by antiferromagnetic coupling between Cu and Mn magnetic moments below TC=361 K. The partial replacement of Cu2+ by Mn3+ cations does not change the symmetry or space group of La(Cu3-xMnx)Mn4O12. However, the introduction of Mn3+ cations at the square-planar 6b site, occupied by Cu, increases the valence mixing of Mn3+ and Mn4+ ions at the octahedral 8c site. This drives to an increase in the bonding distances in the MnO6 octahedron and a decrease of the Cu&-O distance in the CuO4 polyhedron. Susceptibility measurements indicate that La(Cu3-xMnx)Mn4O12 becomes magnetically ordered below TC=310 K for x=1 and below TC=150- 2002;K for x=2. Neutron powder diffraction (NPD) data reveal a parallel arrangement between the (Cu/Mn)6b and Mn8c moments, in contrast with the antiferromagnetic arrangement described in LaCu3Mn4O12. At low temperature, the ordered magnetic moments determined from NPD data on the 8c Mn site are 2.66(4)muBeta and 2.17(6)muBeta for x=1 and x=2, respectively. For the 6b site, the magnetic moments of the Cu/Mn atoms are 0.72(5)muBeta and 0.75(7)muBeta for x=1 and x=2, respectively.