Abstract
The electrical and magnetic transport behaviour of composite samples of (1−x)La0.67Ca0.33MnO3+xFe3O4 with x = 0, 0.1%, 1% and 2% were studied in a temperature interval 10–300 K and for magnetic fields H = 0, 0.3, 0.5, 1 and 3 T. The temperature and magnetic field dependence of resistivity of composites show that the low Fe3O4 doping levels have important effects on electrical and magnetic transport behaviour of La0.67Ca0.33MnO3. Especially, compared to pure La0.67Ca0.33MnO3, a new insulator–metal (I–M) transition was observed at a lower temperature TP2 in all Fe3O4 doped La0.67Ca0.33MnO3 composites, which may result from the existence of a new phase related to Fe3O4 dopant at grain boundaries and surfaces of La0.67Ca0.33MnO3 phases. It is of interest to note that the new I–M transition temperature, TP2, is almost independent of the magnetic field. Meanwhile, an obvious magnetoresistance effect was observed between temperatures TP1 and TP2. The results were discussed by considering the results of scanning electron microscopy, x-ray diffraction, dielectric relaxation and susceptibility analysis.
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