Formation and Characterization of Magnetic Multilayer Ni/Cu Nanowires
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Formation and Characterization of Magnetic Multilayer Ni/Cu Nanowires R. S. Liu1,2, S. C. Chang1, S. F. Hu2,3 and C. Y. Huang2,4 1
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan 2
Taiwan Spin Research Center, National Chung Cheng University, Chia-Yi 621, Taiwan 3 National Nano Device Laboratories, Hsinchu 300, Taiwan 4 National Taiwan Normal University, Taipei 116, Taiwan
ABSTRACT Highly ordered composite nanowires with multilayer of Ni/Cu, have been fabricated by pulsed electrodeposition into nanoporous alumina membrane. The diameter of wires can be easily controlled by pore size of alumina, ranging from 30 to 100 nm. The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer (VSM) measurements. From the result of MFM analysis, the magnetic multilayer nanowires indicate unique magnetic property. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated domain like magnet. This technique has potential for use in the measurement and application of magnetic nanodevices. INTRODUCTION Magnetic nanomaterials fabricated by various methods [1], have attracted a great deal of attention for fundamental interest and technological applications such as magnetic storage media, sensors and magnetic random access memory (MRAM). In these nanomaterials, each ferromagnetic region is single domain which the magnetic spins are aligned to one direction. Thus every ferromagnetic region represents a single domain magnet, which exhibits unique magnetic properties for further application, such as high squareness and high coercivity [2]. Among these nanomaterials, nanowires are of intense interest. Many methods for the fabrication of nanowires have been developed [3,4]. Among these methods, template synthesis was regarded as quite useful because it is extremely general with regard to the types of materials that can be prepared. Recently, considerable success in the preparation of nanowires arrays of metals, polymers, and so on. Many ferromagnetic nanowires of Fe, Co, Ni and their alloys are fabricated by this method. The shape and size of nanowires synthesized by template method can be confined with the pores of the template [5]. However, these nanowires often loss their high coercivity due to demagnetization by neighboring magnetic domains. In order to overcome this drawback, the non-magnetic layer (NM) is inserted between each ferromagnetic layer (FM), to form FM/NM/FM… periodic structure. The magnetic properties of these multilayer nanowires can be varied with the thickness of FM and NM layers [6]. In this work we report the synthesis of an array of Ni/Cu composite nanowires. The relationship between magnetic properties and layer thickness are discussed. The potential use of magnetic multilayer nanowires is also
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described. EXPERIMENTAL DETAILS
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