Neutron diffraction, Mössbauer and magnetotransport study of Fe-substituted derivatives ofCaCu3Mn4O12 perovskite with colossal magnetoresistance

Abstract

The effect of replacing Mn for Fe in the ferrimagnetic perovskiteCaCu3Mn4O12 has been studied in the series of nominal compositionCaCu3(Mn4−xFex)O12 (x = 0, 0.5, 1.0). These materials have been prepared in polycrystallineform under moderate pressure conditions of 2 GPa, in the presence ofKClO4 as oxidizingagent. The x = 1.0 sample has been studied by neutron powder diffraction and Mössbauer spectroscopy tounravel some structural peculiarities. These oxides crystallize in the cubic space group (No. 204) and contain Ca2+ and (Cu2+,Mn3+) at the Asublattice of the ABO3 perovskite, arranged in a 1:3 ordered array. Neutron diffraction suggests thatMn4+ and Fe3+ occupy at random the octahedral B positions of the perovskitestructure, whereas the Mössbauer study adds a singular feature: 89% ofFe3+ is, effectively, in an octahedral environment, whereas 11% ofFe3+ is located at square-planar positions together withCu2+. The materials have also been characterized by magnetic and magnetotransportmeasurements. All the samples are ferromagnetic and show a progressive decrease ofTC as the Fe contents increases. Also the saturation magnetization and Weiss temperaturesdiminish in the Fe-doped oxides, which suggest an increment of the antiferromagneticinteractions at the (Mn, Fe) octahedral sublattice. The magnetoresistance alsodecreases upon Fe doping, although a sharp low-field response is observed belowTC.