Structure, magnetic and transport properties in perovskites

Structure, magnetic and transport properties of manganites have been studied. Samples with show ferromagnetic behaviour. For higher concentrations an important influence of antiferromagnetic interactions has been observed. The sample shows an antiferro-ferromagnetic transition induced by the applied field and the composition is an antiferromagnet, but ferromagnetic interactions are still present. The resistivity of the samples shows a semiconductor-metallic transition for . For x = 0.2 and 0.7 the compounds exhibit insulating behaviour down to 10 K, but a field induced transition to a metallic state is found in . The results are discussed in terms of the charge localization probably due to the covalent character of the Bi.