Template Assisted Fabrication and Magnetic Properties of Cobalt Ferrite Nanostructures
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Template Assisted Fabrication and Magnetic Properties of Cobalt Ferrite Nanostructures Jian H. Zhang, Liyin Chen and Xylona L. Williams Department of Chemistry, Xavier University of Louisiana, 1 Drexel Drive, New Orleans, LA 70125, U.S.A ABSTRACT Spinel cobalt ferrite nanotubes and nanowires of about five micrometers in length were fabricated using anodic aluminum oxide (AAO) templates of 20 – 200 nm pore diameters and sol-gel processing. A cobalt ferrite sol was prepared by mixing the acetic acid solution of cobalt (II) acetate and ethanol solution of iron (III) acetylacetonate. The templates filled with precursor were obtained after they were dipped into the sol and dried in air. The template/precursor composites were sintered in air at 500 ºC to form cobalt ferrite phase, which was verified by XRD. The morphology of the nanostructures determined by SEM revealed that the cobalt ferrite nanotubes were formed in the channels of 100 nm and 200 nm diameters in the templates, whereas the nanowires were formed in the 20 nm channels of the templates. The magnetic measurement of cobalt ferrite nanowires by a SQUID magnetometer showed that the nanowires are superparamagnetic at room temperature. The room temperature measurement of magnetization versus the applied field on the nanowire arrays in 20 nm channels of templates showed that the coercivity is 1.57 kOe and 1.47 kOe for the nanowire axis parallel and perpendicular to the applied field, respectively, indicating that the nanowire arrays are nearly magnetically isotropic. However, the coercivity of cobalt ferrite nanowires fabricated in this work is much larger than those in the similar systems reported in the literatures. INTRODUCTION In the last two decades, nanostructured spinel magnetic ferrites of the general formula, MFe2O4 where M is a divalent metal ion, have attracted extensive research due to their chemical and mechanical stability and varieties of magnetic properties. More importantly, their magnetic properties depend on the size, the shape and the cation distribution in the crystal structure, which can be altered or tailored according to the needs by many synthetic methods, in particular, low temperature chemical methods such as precipitation and sol-gel processing. Therefore, the nanostructured magnetic ferrite materials have found applications in many areas. One area that has attracted growing interest is biomedical and biological area, including magnetic resonance imaging, drug delivery and hyperthermia [1, 2]. So far most research on nanostructured ferrites has focused on the nanoparticles and thin films. Recently, template assisted fabrication of nanotubes has been of considerable interest, since the pore diameter and thickness of the template can be controlled which results in the tunable payload of the nanotubes. Moreover, the nanotubes can be differentially functionalized on their inner and outer walls [3, 4]. Among the spinel magnetic ferrites, cobalt ferrite (CoFe2O4) is of special interest since it is an only hard ferrite. It possesses high coerc
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