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The magnetic, structural, and transport properties of single-layer magnetite (Fe3O4) films prepared by reactive sputtering were investigated. Magnetoresistance (MR) was measured at various thicknesses and temperatures. The increase in MR with thickness is related to grain crystallinity and size, as confirmed by transmission electron microscopy. MR arises from intergranular tunneling, which is supported by the temperature dependence of resistivity (logρ∼T−1∕2). Field-dependent MR correlates with the M curve. Magnetoresistance versus magnetization curves clearly show that the MR effects come from the surface spin arrangement near the grain boundaries. The dependence of MR on the magnetic field observed in polycrystalline Fe3O4 films can be attributed to a surface magnetization near the grain boundary, which will be discussed.

Dielectric properties and microstructure of nano-MgO dispersed Ba 0.3 Sr 0.7 Ti O 3 thin films prepared by sputter deposition J. Appl. Phys. 98, 014107 (2005); 10.1063/1.1947390 Magnetoresistance of polycrystalline Fe 3 O 4 films prepared by reactive sputtering at room temperature