Correlation between structure and magnetic and magnetotransport properties of La0.7Pb0.3(Mn1-xCox)O3 (0-1≤x≤0.3) CMR manganites

Structural and magnetic properties of La0.7Pb0.3(Mn1-xCox)-O-3 (0.1 <= x <= 0.3) manganites are reported. Samples were fabricated by the sol-gel low temperature method. At room temperature, the first structural characterisation of all phases gave as a result the rhombohedral space group (R (3) over barc). All compositions show ferromagnetic behaviour and magnetoresistance. The measured low-temperature magnetic moment and the Curie temperature continuously decrease with respect to the undoped composition, as Mn ions are substituted progressively by Co. This is interpreted in terms of substitution of Mn3+ by Co3+ and the appearance of a small amount of Co4+. The measured magnetoresistance reaches 40% for the 10% Co-doped one at the corresponding Curie temperature. The resistivity behaviour of all the studied compounds is determined by the intra- and intergrain conduction mechanisms, with grain sizes in the range of 10-25 nm. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheirn, Germany, 2006)