MnZn-ferrite/SiO2 particle composites are prepared by mechanical ball ing. We study the relations of effective permeability μ, specific magnetization σ and coercivity Hc with the MnZn-ferrite concentration. The results indicate that an abrupt change emerges in effective permeability when the volume percentage of MnZn-ferrite particles is near V=98%, which means that a magnetic percolation phenomenon occurs in the system. Meanwhile, it is found that the coercivity Hc exhibits an anomalous behaviour that depends strongly on the microstructure of the composite. Above the percolation threshold, the variation of coercivity can be mostly explained in terms of dipolar interaction between magnetic particles, whereas below the percolation threshold, the decrement of Hc is ascribed dominantly to increasing specific magnetization σ. At the same time, we determine the measured percolation threshold Vc=97. 9%, which can be derived from the maximum of d2μ/dV2.
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