Mossbauer study for La0.7M0.3Mn1-xFexO3-y system. (M = Pb, Sr, 0.01 <= X <= 0.3)

On cooling the compounds of the form La1-xMxMnO3-y (where M is divalent cat ion) show a large decrease in resistivity associated with a paramagnetic to ferromagnetic transition. This transition is known to produce a large nega tive magnetoresistance, the so-called colossal magnetoresistance (CMR), nea r the Curie temperature, Tc. In this work the phases La0.7Sr0.3Mn1-xFexO3-y (0.01 less than or equal to x less than or equal to 0.3) have been prepared using the ceramic method, a nd have been characterised by X-ray diffraction, magnetic measurements and Mossbauer spectroscopy. The substitution of the Mn ions by Fe ions gives a large decrease of the Curie temperature of La0.7Sr0.3Mn1-xFexO3-y system. T he samples La0.7Pb0.3Mn1-xFexO3-y (0.01 less than or equal to x less than o r equal to 0.3) were synthesised by the sol-gel low temperature method. The Mossbauer spectra for all compounds exhibit a splitted peak resulting from ions Fe3+ located in the distorted octahedral site. As the content of Fe3 increased the cuadrupole splitting of Fe increased.