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Structure and Magnetic Properties of Magnetic Nanowire Arrays

Author: XuYongSheng
Tutor: WenGeHui
School: Jilin University
Course: Condensed Matter Physics
Keywords: AAO pulse electrochemical deposition nanowires shape anisotropy
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 92
Quote: 1
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Abstract


In recent years, magnetic nanowires have attracted much attention because they have potential application in high-density magnetic recording media. The expected recording density could be as high as 400 GB/in2. In this work, Fe、Co and FeCo alloy nanowires were formed in the pores of porous anodic aluminum oxide template (AAO) by pulse electrochemical deposition. Through the oxidation of FeCo nanowires arrays, cobalt ferrite nanowires were prepared. The morphology、structure and magnetic properties of the nanowires were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM).Porous anodic aluminum oxide template (AAO) was fabricated by two-step anodization. The pores of the template are orderly arranged, have a narrow size distribution, and with an average pore diameter of about 50nm. The Fe Co and FeCo alloy nanowires were formed in the pores of AAO template using pulse electrochemical deposition. The diameter of the nanowires is equal to the pore size of the template. The aspect ratio of the nanowires is over 200. The results showed that the Fe nanowires are body-centered cubic (bcc) structure, and may have a preferred growth orientation of (110). The crystal structure of Co nanowires is hexagonal close-packed (hcp) structure. FeCo alloy nanowires are body-centered cubic disordered alloy, and atomic ratio of Fe and Co is close to the molar ratio of Fe and Co in the deposition electrolyte. Fe、Co、FeCo alloy nanowire arrays show clearly magnetic anisotropy, easy magnetization direction is along nanowires’long axis direction. This is mainly due to shape anisotropy. The nanowire arrays have high remanence ratio (Mr / Ms) and coercivity (Hc) when magnetic field is parallel to the nanowires, and the remanence ratio and coercivity are small when magnetic field is perpendicular to the nanowires. The FeCo alloy nanowire arrays’remanence ratio and coercivity can be tuned by changing the Fe, Co molar ratio in the deposition electrolyte. The FeCo alloy nanowire arrays with proper proportion have larger remanence ratio (Mr / Ms) and coercivity (Hc) than Fe or Co metallic nanowire arrays when the magnetic field is parallel to nanowires’long axis.Cobalt ferrite nanowire arrays were prepared by heat treatment of FeCo alloy nanowire arrays in air. The FeCo alloy nanowires were oxidized to cobalt ferrite nanowires during heat treatment. The XRD spectra show that the cobalt ferrite nanowire arrays have spinel structure. Magnetic properties of FeCo alloy nanowires and cobalt ferrite nanowires were compared. The cobalt ferrite nanowires have a larger coercivity than the FeCo alloy nanowires, this should be due to the formation of cobalt ferrite with larger magneto crystalline anisotropy.

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