Abstract
A systematic study of oxide coated magnetic nanoparticles is carried out to understand and evaluate the effect of oxide tunnel barrier on the magnetoresistance (MR) of magnetite core-shell nanocompacts. SiO2 and ZnO coated Fe3O4 nanoparticles with a shell thickness of ∼2nm have been synthesized and characterized. Magnetic measurements on oxide coated Fe3O4 nanoparticles reveal blocking behavior and superparamagnetism below ∼200K. The magnitude of electrical resistivity at room temperature of SiO2 and ZnO coated Fe3O4 compacts is found to be two to five orders higher than that of pure nanocrystalline Fe3O4 compacts due to resulting insulating oxide layer between magnetite domains. For these nanocompacts, large low field magnetoresistances of −11.5% and −5.8% are achieved in an applied magnetic field of 1T at 100K that could have origins of spin-dependent tunnel MR across the nanometric granules of Fe3O4 safely embedded in insulating oxide matrix.
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