Crystal and magnetic structures of the complex perovskites LaCu3(Mn4–x Fe x )O12 with colossal magnetoresistance

Abstract

Abstract We have studied the series of nominal composition LaCu3(Mn4–x Fe x )O12 (x = 0.5, 1) where Mn is replaced by Fe cations in the ferrimagnetic perovskite LaCu3Mn4O12. These materials have been synthesized in polycrystalline form under moderate pressure conditions of 2 GPa, in the presence of KClO4 as oxidizing agent. All the samples have been studied by neutron powder diffraction (NPD) at room temperature (RT) in order to study the crystal structure. The sample with nominal x = 1 has also been studied by NPD at low temperature to determine its magnetic structure. These oxides crystallize in the cubic space group Im-3 (No. 204) with general formula A'A3B4O12 and contain La3+ and (Cu2+, Mn3+) at the A sublattice of the perovskite, in a 1 : 3 ordered arrangement. NPD suggests that Mn4+/Mn3+ and Fe3+ occupy at random the octahedral B positions of the perovskite structure. The materials have also been characterized by magnetic and magnetotransport measurements. All the samples are ferrimagnetic and show a progressive decrease of T C as the Fe content increases. The replacement of Mn3+ cations by Fe3+ at the octahedral sublattice give rise to a decrease of T C since the Fe ions disturb the ferromagnetic interactions within this magnetic sublattice. The introduction of Fe changes the resistivity response from metallic to a semiconductor behavior. However, the magnetoresistance remains unchanged upon Fe doping and a sharp low-field response is observed below T C.