Magnetic and electrical behaviour of La0.67Ba0.33Mn1 − xFexO3 perovskites

(La0.67Ba0.33)Mn1 − xFexO3 manganites compounds have been prepared by doping up to 20% of Fe at the Mn site. As previously reported in the literature paramagnetic (PM) to ferromagnetic (FM) phase transition has been observed in materials with low Fe doping (≤ 10%). In our x = 0 and x = 0.05 compounds the Curie temperature (TC) is close to room temperature. Above 10% Fe amount, specimens exhibit a glass magnetic behaviour with a spin- or cluster-like freezing process that can be related to a loss of ferromagnetic double exchange interaction. Below 10% of Fe3+ doping electrical-resistivity measurement shows metal – semiconductor transition with a maximum peak of resistivity (ρmax) at a temperature TP close to TC. Above 10% of Fe3+ doping amount the materials exhibit only semiconductor behaviour. Both TC and TP decrease with doping rates with an increasing difference in temperature (TP being lower than TC). Results are consistent with a reduction of the number of available hopping sites for the Mn eg(↑) electron due to substitution of Mn3+ by Fe3+ that suppress the double exchange (DE) interactions.