Fe3O4/a-C/n-Si junctions were formed by sequent depositing a-C and Fe3O4 layers on Si substrates by facing-target magnetron sputtering. The junctions exhibit nonlinear and slightly asymmetric current-voltage behaviors. For the junctions with thinner a-C layers, high value of the ideality factors suggests that the current transport is primary dominated by thermionic field emission other than thermionic emission. The tunneling is found as the dominant mechanism for the junctions with thicker a-C layers. Compared to Fe3O4/n-Si junctions, the positive magnetoresistance in the Fe3O4/a-C/n-Si junctions was enhanced. Magnetoresistance is considered to originate from the interfacial scattering of carriers where the energy band of Fe3O4 is modified by the defect states. A possible mechanism for the enhancement of magnetoresistance is the heavier intermixing between Fe3O4 and a-C layer, which leads to a stronger scattering with the increase of a-C layer thickness. (c) 2011 Elsevier B.V. All rights reserved.