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Abstract: The effect of Fe doping on the ferromagnetic Nd0.7Pb0.3Mn1− x Fe x O3 (, 0.025, 0.05, 0.075, 0.1) phases has been studied in order to analyze the double-exchange interaction. The structural and magnetic study has been carried out by neutron powder diffraction and susceptibility measurements between 1.7 and 300K. The substitution of Fe at the Mn site results in reductions in both the Curie temperature T c and the magnetic moment per Mn ion without appreciable differences in the crystal structures. All the compounds crystallize in space group. The thermal evolution of the lattice parameters of the Nd0.7Pb0.3Mn1− x Fe x O3 (, 0.05, 0.075) compounds shows discontinuities in volume and lattice parameters close to the magnetic transition temperature. Increasing amounts of Fe3+ reduces the double exchange interactions and no magnetic contribution for is observed. The magnetic structures of Nd0.7Pb0.3Mn1− x Fe x O3 (, 0.025, 0.05, 0.075) compounds show that the Nd and Mn ions are ferromagnetically ordered. [Copyright &y& Elsevier]

The double perovskites, Sr2FeReO6 and Sr2FeRe0.9M0.1O6 (M=Nb, Ta) have been obtained by soft synthesis methods which yield homogeneous particles of micrometric grain size. The materials have been studied by X-ray and neutron powder diffraction, scanning electron microscopy and magnetic measurements. Rietveld refinements show that the compounds adopt a tetragonal I4/mmm structure at high temperatures and monoclinic P21/n below the transition temperature. The magnetic structures were determined by neutron powder diffraction at 100 and 300 K for the Sr2FeReO6, Sr2FeRe0.9Nb0.1O6 and Sr2FeRe0.9Ta0.1O6 phases, respectively. Evidence for a ferrimagnetic coupling between the Fe3+ and Re5+ sublattices has been observed. Magnetic measurements yield magnetic moments lower than the theoretical ones being in accord with the antisite disorder of 25% in the B–B′ positions. [Copyright &y& Elsevier]