Synthesis and room-temperature ferromagnetism of cobalt-doped SnO 2 nanowires
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Yongsheng Zhang Department of Mathematics and Physics, Luoyang Institute of Science and Technology, Luoyang 471023, People’s Republic of China
Lijun Li and Ziqiang Zhu Key Lab for Polar Materials and Devices of Ministry of Education and Department of Electronic Engineering, East China Normal University, Shanghai 200241, People’s Republic of China (Received 31 October 2008; accepted 1 December 2008)
We have observed ferromagnetism in dilute cobalt-doped SnO2 nanowires at room temperatures. The Co-doped SnO2 nanowires with an average diameter of 50 nm were synthesized by the thermal chemical vapor transport method. High-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy analyses demonstrate that the nanowires are single-crystal structures and Co is homogeneously doped into the SnO2 lattice. The ferromagnetic hysteresis curves and temperaturedependent magnetization measurement provide evidence for ferromagnetic properties with a Curie temperature above room temperature. Oxygen annealing has been performed to study the roles played by the oxygen vacancies in determining the ferromagnetic properties of the nanowires. I. INTRODUCTION
In recent years, great interest has been focused on the rapidly developing field of spintronics, which embodies the notion of simultaneously manipulating both charge and spin in a single semiconductor medium. The diluted magnetic semiconductors (DMS) that transforms spinfrustrated semiconductors into ferromagnets by magnetic doping have become the most promising candidates for many spintronic applications due to compatibility with present semiconductor devices.1 Since the theoretical and experimental work of Dietl et al.2 and Matsumoto et al.,3 many groups have done profound studies on roomtemperature ferromagnetism (RTFM) in various types of transition-metal (TM)-doped wide band gap semiconducting oxide materials, such as ZnO,4,5 TiO2,6,7 and SnO2.8–12 Among these oxides, SnO2 is a very interesting oxide semiconductor optical material with a wide band gap of 3.6 eV.13 Its high optical transparency and electrical conductivity make it an attractive material for a variety of applications requiring combined magnetic and optical functionality. More recently, ferromagnetism above room temperature has been reported in TM-doped SnO2. Ogale et al.8 reported a Curie temperature close to 650 K in a Sn0.95Co0.05O2-d thin-film sample with an astonishingly a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0236 J. Mater. Res., Vol. 24, No. 6, Jun 2009
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large magnetic moment reported as 7.5 mB/Co. Subsequently, high-temperature ferromagnetism was reported for Sn0.86Fe0.14O2 with a moment of 1.8 mB/Fe.9 However, to date, the research on the TM-doped SnO2 mainly pays attention to the thin films materials. As we know, few reports on the magnetic properties of TM-doped SnO2 nanowires have been reported thus far. Compared with films, one-dimensional nanowires attract much attenti
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