Room-temperature magnetoresistance effects of Ag-added Fe3O4 films with single-domain grains

Polycrystalline Agx(Fe3O4)1−x films (x=0x=0, 0.1, 0.2 and 0.3) have been prepared by the sol–gel method in combination of the spin-coating technique with a precursor solution containing polyvinyl alcohol (PVA) on fused quartz substrates. XRD analysis and SEM images indicate that the Fe3O4 grains are nearly spherical single-domain particles. The coercivities of the films are about 290 Oe for x=0.1x=0.1 and 360 Oe for x=0.3x=0.3, respectively, which are nearly the same as the magnetocrystalline anisotropic effective field HKHK of Fe3O4. At 300 K, the x=0.1x=0.1 film has a maximal magnetoresistance of −8.7% at a magnetic field of 50 kOe and −3.5% at 8.8 kOe, while the pure Fe3O4 film is only −2.2% at 8.8 kOe. This enhancement of the MR can be attributed to the contribution from the spin-dependent scattering at the Ag–Fe3O4 interfaces as well as the spin-polarized tunneling at boundaries of Fe3O4 grains of the spin-polarized electrons. In addition, different MR behaviors for Ag-added Fe3O4 bulk polycrystalline samples and polycrystalline films are discussed.