Structural, magnetic and magnetotransport properties of La0.7Pb0.3Mn0.9TM0.1O3 (TM = Fe, Co, Ni) CMR perovskites

Neutron-diffraction. magnetic and transport measurements have been used in order to study the structural and magnetic changes of the magnetoresistive La0.7Pb0.3Mn0.9TM0.1O3 (TM = Fe, Co, Ni) perovskite-like compounds. Samples were prepared by the sol-gel low-temperature method. In all cases the exact stoichiometry is slightly different from the nominal one probably due to the presence of cation vacancies. All the phases exhibit ferromagnetic behaviour and magnetoresistance. No appreciable differences in the structure, as the TM3+ ion changes, have been observed. The magnetic moment and Curie temperature continuously decrease (with respect to the undoped composition) with the substitution of Mn atoms by Ni, Co or Fe, respectively. The magnetoresistance (MR = DeltaR/R(0)), under 0 and 6 T applied fields, has been measured reaching a magnitude of about 65% in the ease of the 10% Fe doped sample. The obtained results can be interpreted in terms of ferro- or antiferromagnetic exchange competitions between Mn3+-Mn4+ and TM3+-Mn4+ pairs.