The microSVUctures of a?-deposited CO-Ag nano-granular films are characterized by x-ray diffraction, transmission electron microscopy and high-resolution electron microscopy. In as-deposited films, there is a strong tendency for phase separation to occur; Co and Ag particles coexist m the films. The average size of CO grains varies with the CO concentration. Ag particles have the preferential lattice orientation (110) and Co particles have lanice orientations (110). ( 111). (LIZ), and (100) in the direction of the film surface normal. There is a tendency for two connecting grains to have two groups of parallel lauice planes.

Two sets of polycrystalline manganites with the composition Sm1/2Sr1/2MnO3 were prepared using the sol–gel (SG) and the solid-state reaction (SSR) methods. It is found that the magnetotransport properties for both sets of samples with the same composition are very strongly dependent on their preparation methods. For the SG samples, insulating behaviour at zero magnetic field over a temperature range from 70 to 300 K, and a metal–insulator transition with a huge reduction in resistance near TC ∼ 100 K under a sufficiently high magnetic field over 2 T, which lead to a maximum magnetoresistance ratio value up to 105% at 2 T and over 106% at 5 T near 65 K, were observed. However, for the samples prepared by the SSR method the resistance (R)–temperature (T) curve only showed a single insulator–metal transition. At the same time, their temperature-dependent magnetizations, M(T), are also totally different. The morphologies obtained by scanning electron microscopy demonstrate that there is a large difference in microstructure between the two sets of samples. The fine grains and a large number of grain boundaries are primary factors leading to the insulating characteristics at zero field and the unique transport properties induced by a sufficient magnetic field in the SG samples.

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