Abstract
We study the dependence of resistivity ρ on graphite volume fraction p in Fe 3O 4/C magnetic composite. The measured percolation threshold, p c was determined to be 0.212 and 0.231 at 300 and 77 K, respectively. The difference in values of p c can be attributed to the variation in the value of ρ Fe 3O 4 / ρ c. Experimental results indicate that the conductivity exhibits non-universal critical behavior. The non-universal critical exponent t is 3.88±0.20 (300 K) and 3.18±0.26 (77 K), which may be related to cavities in powder composite. Transport mechanisms were also discussed with temperature dependence of resistance and I–V characteristics. It is considered that decreasing electrical transport at 77 K leads likely to low critical exponent t in contrast to 300 K.
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