Abstract
Regarding the perovskite oxides AA′3B4O12, we have investigated the solid solution CaCu3(Ru4−xMnx)O12 (0 ≤ x ≤ 4), where the two end members present very different properties: Pauli-paramagnetic and metallic for x = 0 versus ferrimagnetic and half-metallic with colossal magnetoresistance for x = 4. We have prepared x = 0, 0.5, 1.0, 1.5, 2.0, and 3.0 members. All of the samples crystallize in the cubic space group Im3− (No. 204). The unit-cell parameter, volume, and bond distances evolve linearly along the series, decreasing as Mn content (x) increases. The x = 2 sample has been selected for use in a neutron diffraction study of both structure and magnetism. Low-temperature neutron powder diffraction data allowed us to probe the microscopic origin of the magnetism. Unlike the ferrimagnetic end-member with x = 4, we have found that the magnetic arrangement for x = 2 is ferromagnetic, with the magnetic moments of Cu and (Mn, Ru) oriented along the same direction. Resistivity and magnetic susceptibility measurements of this series were also analyzed: the introduction of Ru increases the number of charge carriers in the compound, leading to metallic behavior and a drastic decrease of the magnetoresistance. The magnetic ordering temperature, TC, has also been found to increase as Mn content in the compound increases.
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