Abstract
A series of bulk polycrystalline Ag-added Fe 3O 4 with a nominal composition, (Fe 3O 4) 1− x Ag x ( x is molar fraction) with x=0, 0.1, 0.2, 0.3, 0.4, and 0.5 have been prepared by conventional solid-state reaction. X-ray diffraction patterns show that the pure Fe 3O 4 sample ( x=0) has a single-phase inverse spinel structure, while the Ag-added samples are two-phase composites consisting of a ferrimagnetic Fe 3O 4 phase and a non-magnetic metal Ag phase. The bright-field transmission electron microscopy images exhibit that the samples are typical granular solids with a porosity of about 22%. The addition of Ag slightly increases the average grain size of the Fe 3O 4 phase and significantly enhances the MR effect of bulk polycrystalline Fe 3O 4 samples. Of all the samples the x=0.3 sample has a maximal MR of −5.1% at 300 K in a magnetic field of 1 T, and −6.8% in 5 T, which are approximately three times greater than the corresponding MR values (−1.8% at 1 T and −2.4% at 5 T) of the Fe 3O 4 sample. This enhancement of the MR can be attributed to the combination effect from the spin-dependent scattering at the interfaces between the Fe 3O 4 grains and the Ag granules and the spin-polarized tunneling at grain boundaries of Fe 3O 4 phase of the spin-polarized electrons.
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