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

Abstract

The magnetoresistance (MR) of polycrystalline composites of ferromagnetic (FM) (M,Fe) 3 O 4 (M 5 Mn, Co, Ni, and Zn) spinel ferrite and weak FM a-Fe 2 O 3 insulator with spin canting was investigated. Sample disks were prepared by conventional solid-state sintering of a-Fe 2 O 3 , with either Mn 2 O 3 , Co 3 O 4 , NiO, or ZnO in a mixing ratio of M/Fe 5 x/(3Àx) 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 /a-Fe 2 O 3 composite (x 5 0.25) sintered under air. The temperature dependence of the electrical resistivity showed a ln(q)pT À1/2 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 a-Fe 2 O 3 barrier of several micrometer thickness. The MR may be attributed to spin polarization in the ferrite grains coupled with the a-Fe 2 O 3 insulating barrier, where its spins are slightly canting in strong anti-FM interaction. P. A. Joy-contributing editor *Member, The American Ceramic Society.

Magnetoplumbite and W-type barium ferrites as magnetic mixture with hematite

“…10) The MR effect was recently found out on sintered compacts of spinel ferrite mixtures with α-Fe2O3. 11) Barium hexaferrite; BaFe12O19 (hereafter denoted as BaM) is one of the most famous ferromagnetic materials. It has magnetoplumbite-type structure with space group of P63/mmc (a = 0.589 nm and c = 2.32 nm).…”

Probing Ferrimagnetic Semiconductor with Enhanced Negative Magnetoresistance: 2D Chromium Sulfide

“…f) Summary of the figure of merit and roadmap of 2D magnetoresistive devices (detailed data are tabulated in Table S6, Supporting Information); the number denotes the references of earlier reported 2D materials. [ 1,19,37–48 ]…”