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

Authors

  • Yuji Masubuchi,

    Corresponding author
    1. Graduate School of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo 060-8628, Japan
      †Author to whom correspondence should be addressed. e-mail: yuji-mas@eng.hokudai.ac.jp
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  • Makoto Minoya,

    1. Graduate School of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo 060-8628, Japan
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  • Takashi Takeda,

    1. Graduate School of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo 060-8628, Japan
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    • Present address: National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.

  • Shinichi Kikkawa

    1. Graduate School of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo 060-8628, Japan
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    • *Member, The American Ceramic Society.


  • P. A. Joy—contributing editor

†Author to whom correspondence should be addressed. e-mail: yuji-mas@eng.hokudai.ac.jp

Abstract

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(ρ)∝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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