Crystal structure, magnetic and electrical properties ofCaCu3Mn4−xTixO12 (0.3 ≤ x ≤ 3.0) perovskites

Abstract

The effect of substituting Ti for Mn in the ferrimagnetic perovskiteCaCu3Mn4O12 has been studiedin the series CaCu3Mn4−xTixO12 (x = 0.3,0.5,1.0,1.5,2.0,3.0). Thesematerials have been prepared in polycrystalline form under moderate pressure conditions of 2 GPa and1000 °C in thepresence of KClO4 as an oxidizing agent. The crystal structure is cubic, space group (No. 204); the unit cell parameters vary linearly froma = 7.2361(4) Å (x = 0.3)to a = 7.3489(5) Å (x = 3.0) at room temperature (RT). A neutron powder diffraction studyhas been performed for a selected sample of nominal compositionCaCu3Mn3TiO12. Inthe ABO3 perovskite superstructure, the A positions are occupied byCa2+ and (Cu2.52+Mn0.53+), ordered in a 1:3 arrangement, giving rise to the body-centring of the unit cell. Atthe B positions, Mn and Ti are randomly distributed over the octahedral sites;(Mn,Ti)O6 octahedra areconsiderably tilted by 19°, due to the relatively small size of the A-type cations. The Curie temperatures decrease from 331 K(x = 0.3) to310 K (x = 3.0). The saturation magnetization at 5 K is strongly reduced upon Ti introduction, fromMs = 10.4 μB fu−1 (x = 0.3)to 1.0 μB fu−1 (x = 3.0).All the samples exhibit negative magnetoresistance (MR), reaching a maximum value of 41% for thex = 0.5 sample at 5 K forH = 9 T; the MR(9 T) at RTis as high as 7% for x = 0.5, and shows an appreciable temperature stability.