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1032-I14-40

Vertically Aligned Mn-doped Fe3O4 Nanowire Arrays: Magnetic Properties and Gas Sensing at Room Temperature Seon Oh Hwang1, Chang Hyun Kim1, Yoon Myung1, Seong-Hun Park1, Jeunghee Park1, Chang Soo Hahn2, and Jae-Young Kim3 1 Department of Materials Chemistry, Korea University, Jochiwon, 339-700, Korea, Republic of 2 Nano-Mechanical Systems Research Center, Korea Institute of Machinery and Materials, Daejeon, 305-343, Korea, Republic of 3 Pohang Accelerator Laboratory, POSTECH, Pohang, 790 - 784, Korea, Republic of ABSTRACT Vertically-aligned Mn (10%)-doped Fe3O4 (Fe2.7Mn0.3O4) nanowire arrays were produced by the reduction/substitution of pre-grown Fe2O3 nanowires. These nanowires were ferromagnetic with a Verwey temperature of 129 K. X-ray magnetic circular dichroism measurements revealed that the Mn2+ ions preferentially occupy the tetrahedral sites, substituting for the Fe3+ ions. We observed that the Mn substitution decreases the magnetization, but increases the electrical conductivity. We developed highly sensitive gas sensors using these nanowire arrays, operating at room temperature, whose sensitivity showed a correlation with their bond strength of diatomic/triatomic molecules. Based on the fact that the sensitivity was highest toward water vapor, an excellent-performance humidity sensor was fabricated. INTODUCTION Currently, interest in magnetic 1D nanostructures (e.g., nanorods, nanowires, and nanotubes) has been steadily increasing, because of their potential application in perpendicular data recording and spintronic devices.[1,2] Iron oxides possess many advantages in technological applications, due to their exclusive combination of magnetic and electrical properties. One of the most important iron oxides, magnetite (Fe3O4), is known to undergo a ferrimagnetic transition at a Curie temperature (TC) of ~850 K. It has an inverse spinel structure, symbolized as [Fe3+]A[Fe2+Fe3+]BO4, in which the A sites (tetrahedral sites) are occupied by the Fe3+ ions, and the B sites (octahedral sites) by equal numbers of Fe2+ and Fe3+ ions. The substitution of one type of iron by another transition metal ion provides a means of controlling their magnetic/electrical properties, which extend their application range.[3,4] Thus, a study of the effect of transition metal doping on the properties of the Fe3O4 nanostructures is of interest from the viewpoint of both fundamental scientific interest and its potential application to various nanodevices. In this study, we first synthesized vertically-aligned Mn (10%)-doped Fe3O4 nanowire (NW) arrays on a large area of the substrates, using the reduction/substitution reaction of pre-grown vertically-aligned αFe2O3 (hematite) NW arrays. The present work is designed to provide valuable information on how the Mn doping influences the magnetic/electrical properties of the Fe3O4 NWs using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). Based on the full characterization of electronic structures, we fabricated gas sensors using the Mn-doped Fe