Magnetic and electrical transport properties of Pb1-xLaxTi1-xMnxO3 ceramics

Pb1-xLaxTi1-xMnxO3 (PLTM100x, x = 0.20, 0.40, 0.50, 0.60, and 0.80) ceramics have been prepared and investigated. X-ray diffractions show all ceramics are crystallized into perovskite structures with tetragonal symmetry for PLTMO20 and orthorhombic symmetry for the other compositions. X-ray photoelectron spectroscopy results confirm that the Mn cations in PLTMO20 and PLTMO40 have the valence state of +3, whereas in other compositions, the Mn cations have mixed valences states of +3 and +4. With increasing x from 0.20 to 0.80, the materials change from superparamagnetic to coexisting ferromagnetic and antiferromagnetic magnetic behaviour whereas all compositions persist insulating behaviour, as confirmed by the magnetization-magnetic field (M-H), the temperature dependent magnetization (M-T) and transport measurements. Especially, the PLTMO80 has a large negative magnetoresistance of 41.5% at 10 K with the applied filed of 2 T. By considering the chemical states of Mn cations, these results are attributed to that the coexistence of metallic ferromagnetic and insulating non-ferromagnetic phases.