Enhanced magnetoresistance in CaCu3(Mn4−xRex)O12 (x= 0, 0.1, 0.2) complex perovskites prepared at moderate pressures

New complex perovskites of the series CaCu(MnRe)O have been prepared from citrate precursors under moderate pressure conditions of 2 GPa and 1000 °C, in the presence of KClO as oxidizing agent to stabilize Mn/Mn mixed valence. The polycrystalline samples have been characterized by x-ray diffraction, neutron powder diffraction (NPD), magnetic, and magnetotransport measurements. The crystal structures are cubic, space group Im-3. The unit-cell parameters increase from a = 7.2379(2) Å for the parent (x = 0) compound to a = 7.2420(4) Å for CaCu(MnRe)O. Both oxides adopt a superstructure of the perovskites ABO with long-range 1:3 ordering for Ca and Cu ions at the A sublattice. For the compound doped with Re (x = 0.1), the result of a NPD study shows that Re ions are randomly located at the octahedral positions, being the (Mn,Re)O octahedra strongly tilted, with superexchange (Mn,Re)-O-(Mn,Re) angles of 142.03°. Neutron diffraction data clearly show that some Mn ions are located together with Cu at the square-planar 6b positions. The magnetic structure determined from low-temperature NPD data unveils a ferromagnetic coupling between (Mn,Re) spins at octahedral positions and weak antiferromagnetism with (Cu,Mn) spins. Interestingly, an enhancement of the magnetoresistance effect is observed for the Re-doped compound, well beyond that found for the parent perovskite.
We thank the financial support of the Spanish Ministry of Economy and Competitiveness to the projects MAT2013-41099-R and RyC-2010-06276.