Effect of heat treatment condition on magnetic, electrical transport and magnetoresistance properties of La0.67Sr0.33MnO3 manganite coatings

Abstract

Effects of three different heat treatment conditions (air, vacuum and nitrogen) on the structure, magnetic, electrical transport and low-field magnetoresistance behaviors of La0.67Sr0.33MnO3 manganite coatings synthesized by sol-gel and screen printing methods have been systematically investigated. The detailed crystallographic analyses revealed that the diffraction peak positions of the samples subjected to annealing in vacuum and nitrogen ambients shifted to lower-angle regions, and lattice parameters and structure distortion increased as compared with those of the sample annealed in air, which were due to the introduction of oxygen deficiency under the annealing conditions of vacuum and nitrogen. The content of oxygen deficiency of the samples could be determined by the change of lattice parameters. Furthermore, the vacuum and nitrogen annealed samples exhibited a dramatic increase in the resistivity, accompanied by the reduction in ferromagnetism, the resistivity peak temperature and the ferromagnetism transition temperature. These phenomena were attributed to the decrease of average manganese oxidation state, as a result the mobile charge carriers were reduced, the ferromagnetic coupling and the double exchange effect between manganese ions decreased while the magnetic inhomogeneity increased. In the meanwhile, magnetoresistance ratios of the oxygen-deficient samples were enhanced around the percolation threshold.