Structure, magnetic and transport properties in La0.7-xBixCa0.3MnO3 (0.05 less than or equal x less than or equal 0.7) perovskites

摘要

Structure, magnetic and transport properties of La0.7-xBixCa0.3MnO3 (0.05 less than or equal x less than or equal 0.7) manganites have been studied. Samples with x less than or equal 0.15 show ferromagnetic behaviour. For higher concentrations an important influence of antiferromagnetic interactions has been observed. The La0.5Bi0.2Ca0.3MnO3 sample shows an antiferro-ferromagnetic transition induced by the applied field and the Bi0.7Ca0.3MnO3 composition is an antiferromagnet, but ferromagnetic interactions are still present. The resistivity of the samples shows a semiconductor-metallic transition for x less than or equal 0.15. 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 La0.5Bi0.2Ca0.3MnO3. The results are discussed in terms of the charge localization probably due to the covalent character of the Bi.