Tunneling magnetoresistance in sintered Fe3O4 samples diluted with Fe and α-Fe2O3

Electric transport and magnetoresistance characteristics were investigated for Fe3O4-x Fe(x=0, 10, 20 wt.%) samples and Fe3O4-alpha-Fe2O3 samples sintered at 500degreesC. For composition dependence of Fe3O4-x Fe samples, the largest room temperature MR, 3.3% at 10 kOe, was obtained from a Fe3O4-10 Fe sample. For the surface heat treatment dependence of Fe3O4 powders, the largest room temperature MR, 4% at 10 kOe, was obtained from a Fe3O4-alpha-Fe2O3 sample sintered with Fe3O4 powders heated at 200degreesC in air. It was found that these enhanced MR ratios always appear together with the appropriate excess resistance which is regarded as the tunneling barrier. These enhanced MR ratios of Fe3O4-10 Fe and Fe3O4-alpha-Fe2O3 samples can be explained by the increased interparticle contact sites and the appropriate thickness of alpha-Fe2O3, respectively.