Four kinds of Fe3O4/Ag granular systems were prepared from sintered mixtures of Fe3O4 and Ag or Ag2O. Magneto-resistances (MRs) were measured at room temperature for samples with Ag volume fraction x between 0 and 0.4. Samples including relatively large Fe3O4 grains showed 1% to 1.4% room temperature MR ratios (MRR) at 1 T. On the other hand, samples including Fe3O4 nano-particles showed large negative room temperature MRR of about-4% to-5% at 1 T near the percolation threshold of xc-0.2. It was suggested that Fe3O4/Ag/Fe3O4 paths were effective for the large IMRRI by the elastic conduction of spin-polarized electrons between Fe3O4 nano-particles. Possibility of spin accumulation in small Ag particles was also shown for this system.

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