| Magnetoresistance effects have been investigated for Fe₃O₄ samples sintered with three type Fe₃O₄ powders; commercial Fe₃O₄ powders, Fe₃O₄ powders milled in Ar and ethyl alcohol. The largest MR ratio, 8% at 10kOe, was obtained in Fe₃O₄ sample sintered with powders milled in ethyl alcohol. The enhanced MR ratio appears together with the excess resistance, which regarded as tunneling barriers, at the interface between Fe₃O₄ particles. It indicates that the enhanced MR ratio arises from the spin dependent tunneling effect and can be explained with increased interparticle contacts. On the other hand, high sensitivities of Fe₃O₄ samples at low magnetic fields were achieved by fabricating the rod and ring type hybrid structure, Fe_(19)Ni_(81)/Fe₃O₄/ Fe_(19)Ni_(81). Compared with the MR values, 4%, at 2kOe for single Fe₃O₄ sintered body, same MR values for rod and ring type hybrid structures were obtained at 120Oe and 58Oe, respectively. These high sensitivities at low magnetic fields were attributed to magnetic fields increased by high permeability of Fe_(19)Ni_(81), at the space between the Fe_(19)Ni_(81) bulks. |
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