Preparation, structure and properties of La0.67Pb0.33(Mn1-xCox)O3-δ

Abstract

La0.67Pb0.33(Mn1-xCox)O3-δ ceramics with x=0, 0.01, 0.03, 0.06, 0.1 and 0.15 have been prepared in a two-step procedure. Precursor gels were made by the wet chemical malic acid method. The gels were calcined and then converted into ceramics by heat treatment at 950 °C and 1000 °C in air. X-ray diffraction showed that the compounds were phase pure. The crystal structure symmetry of the compounds was confirmed to be rhombohedral (space group R3c) for the whole investigated range of x. All compounds undergo a paramagnetic–ferromagnetic phase transition between 335 K and 225 K. The basic magnetic characteristics such as the Curie temperature \(\mathit{T}_{\mathrm{C}}\), the paramagnetic Curie temperature θ, the effective magnetic moment \(\mathit{\mu}_{\mathrm{eff}}\) and the saturated magnetization \(\mathit{\mu}_{\mathrm{s}}\) decrease with increasing Co doping. The ferromagnetic transition is accompanied by an anomaly in the electrical resistance for all compounds. The high-temperature insulator–metal transitions (\(\mathit{T}_{\mathrm{p}}\)) do not coincide with the relevant \(\mathit{T}_{\mathrm{C}}\). A large magnetoresistance peak of about 15% was observed for all compounds at \(\mathit{T}_{\mathrm{C}}\).