Abstract :
The influence of Fe3O4 contents on the electrical transport properties (resistivity and ac susceptibility) of a series of composite samples of La0.67Ca0.33MnO3/Fe3O4 is studied. Results show that the Fe3O4 phase not only shifts the intrinsic insulator–metal (I–M) transition temperature TP1 to a lower temperature, but also causes a new I–M transition at a lower temperature TP2 (TP2<TP1). On the basis of an analysis by scanning electron microscopy and X-ray diffraction, we suggest that the decrease of the I–M transition temperature and the formation of the new I–M transition are caused by the segregation of a new phases related to the Fe3O4 at grain boundaries or surfaces of the La0.67Ca0.33MnO3 grains.
