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Electron Transport Under Magnetic Field in Insulating Hematite Composites with Spinel Ferrite

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The magnetoresistance (MR) of polycrystalline composites of ferromagnetic (FM) (M,Fe)3O4 (M=Mn, Co, Ni, and Zn) spinel ferrite and weak FM α-Fe2O3 insulator with spin canting was investigated. Sample disks were prepared by conventional solid-state sintering of α-Fe2O3, with either Mn2O3, Co3O4, NiO, or ZnO in a mixing ratio of M/Fe=x/(3−x) at 1473 K for 10 h under Ar or air atmospheres. The largest MR ratios of 2.02% at room temperature and 11.7% at 77 K were observed under a magnetic field of 0.5 T for the (Mn,Fe)3O4/α-Fe2O3 composite (x=0.25) sintered under air. The temperature dependence of the electrical resistivity showed a ln()∝T−1/2 relationship, which suggests tunneling electron conduction in the granular composite. The MR ratio changed with the magnetization of the (M,Fe)3O4 spinel ferrite, with a maximum at 2.02% where the (Mn,Fe)3O4 ferrite grains were separated with the α-Fe2O3 barrier of several micrometer thickness. The MR may be attributed to spin polarization in the ferrite grains coupled with the α-Fe2O3 insulating barrier, where its spins are slightly canting in strong anti-FM interaction.
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Document Type: Research Article

Affiliations: Graduate School of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo 060-8628, Japan

Publication date: 2011-03-01

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