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Electron Transport Under Magnetic Field in Insulating Hematite Composites with Spinel Ferrite
Author(s) -
Masubuchi Yuji,
Minoya Makoto,
Takeda Takashi,
Kikkawa Shinichi
Publication year - 2011
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2010.04135.x
Subject(s) - materials science , spin canting , spinel , ferrite (magnet) , beta ferrite , sintering , magnetization , electrical resistivity and conductivity , magnetoresistance , analytical chemistry (journal) , non blocking i/o , crystallite , condensed matter physics , hematite , nuclear magnetic resonance , composite material , metallurgy , magnetic field , microstructure , chemistry , austenite , biochemistry , physics , chromatography , quantum mechanics , electrical engineering , engineering , catalysis
The magnetoresistance (MR) of polycrystalline composites of ferromagnetic (FM) ( M ,Fe) 3 O 4 ( M =Mn, Co, Ni, and Zn) spinel ferrite and weak FM α‐Fe 2 O 3 insulator with spin canting was investigated. Sample disks were prepared by conventional solid‐state sintering of α‐Fe 2 O 3 , with either Mn 2 O 3 , Co 3 O 4 , 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) 3 O 4 /α‐Fe 2 O 3 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) 3 O 4 spinel ferrite, with a maximum at 2.02% where the (Mn,Fe) 3 O 4 ferrite grains were separated with the α‐Fe 2 O 3 barrier of several micrometer thickness. The MR may be attributed to spin polarization in the ferrite grains coupled with the α‐Fe 2 O 3 insulating barrier, where its spins are slightly canting in strong anti‐FM interaction.