Abstract
Magnetotransport of Fe3O4-hexabromobenzene (C6Br6) composite has been studied. Powders of C6Br6 and Fe2O3 nanoparticles were mixed together. They were annealed in hydrogen flow. There was a phase transformation from Fe2O3 to Fe3O4 after annealing. Giant negative magnetoresistance (MR) was observed at room temperature and the MR ratio is about 13.4% in an applied field of 5 T. The maximum MR ratio is 21.5% at 130 K. The temperature dependence of the resistivity exhibits characteristics of intergranular tunneling in the samples. The enhancement of the MR ratio is attributed to the fact that the C6Br6 can act as barrier material and, more importantly, can prevent the oxidation of the surface of Fe3O4, which is believed to alter the half-metallic state at the surface.
Highlights
There has been increased interest in the half-metallic magnetiteFe3O4͒ due to its highly spin polarized naturesupposedly ϳ100%͒.1,2 In principle, a high spin polarization should result in large tunneling magnetoresistanceTMRsince the latter is proportional to the spin polarization of the tunneling electrons.3–5 Many studies have focused on the magnetoresistanceMRratio in Fe3O4 of different forms including epitaxial and polycrystalline films, powders, and tunnel junctions.6–10 In early reports, some groups have claimed a large MR response on breaking contact of two microscaled single crystals of magnetite11 and thin film structure composed of a few stacked monolayers of organically encapsulated magnetite nanocrystals.12 in most cases the MR ratio is much smaller than expected, especially at room temperature
We have previously reported that polystyrenePScoated magnetite nanoparticles exhibit drastically enhanced intergranular TMR.18
After powders were annealed at 250 ° C in pure hydrogen flow, the weight ratio of C6Br6 and iron oxide nanoparticles changed to about 1:15 owing to the sublimation of C6Br6
Summary
There has been increased interest in the half-metallic magnetiteFe3O4͒ due to its highly spin polarized naturesupposedly ϳ100%͒.1,2 In principle, a high spin polarization should result in large tunneling magnetoresistanceTMRsince the latter is proportional to the spin polarization of the tunneling electrons.3–5 Many studies have focused on the magnetoresistanceMRratio in Fe3O4 of different forms including epitaxial and polycrystalline films, powders, and tunnel junctions.6–10 In early reports, some groups have claimed a large MR response on breaking contact of two microscaled single crystals of magnetite11 and thin film structure composed of a few stacked monolayers of organically encapsulated magnetite nanocrystals.12 in most cases the MR ratio is much smaller than expected, especially at room temperature. Protection of the surfaces of Fe3O4 from oxidation by the PS coating. The investigation of the MR and spin polarization of the surface of Fe3O4 in a magnetite/organic hexabromobenzeneC6Br6͒ nanocomposite is discussed.
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