Magnetism in Cylindrical NiFe Nanotubes
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1258-Q09-07
Magnetism in Cylindrical NiFe Nanotubes
H.F. Liew, W.C. Junus, X.H. Wang and W.S. Lew School of Physical & Mathematical Sciences, Nanyang Technological University 21 Nanyang Link, Singapore 637371 ABSTRACT
We report the fabrication of ferromagnetic NiFe nanotubes with a wall thickness of 80 nm by electrodeposition in nanoporous templates. The structure and wall thickness of the nanotubes are controlled by the thickness of the conductive layer at the back of the templates. The NiFe nanotubes have shown soft magnetic material properties with high magnetic saturation and low coercivity. The NiFe nanotube arrays are preferentially magnetized in the perpendicular direction to the nanotubes. Micromagnetic simulation results show that a curling mode is perceived with the formation of opposite magnetic vortex states on the end of the nanotube surface during the magnetization process.
INTRODUCTION
Templated growth of magnetic nanotubes in alumina has stimulated great attentions because of their potential applications as solid state memory1-2, advanced magnetic sensors3 and biological transport carriers4. S. J. Son et.al5 claims that the hollow center of the nanotubes can be stored with biomolecules or drugs. In addition, by applying external magnetic field, the encapsulated nanotubes with magnetite layer on the inner surface can be delivery to target organs. Templated synthesis of metallic nanotube using anodic alumina oxide (AAO)6-8 is a proven method because the metal ions can be deposited in the nanoporous more efficiently. This method is simple and is able to produce large quantities of high quality nanotubes. In addition, alloy metal with different composition can be easily deposited from a single bath and is dependence on the electrical potential applied during electrodeposition. Unlike nanowire magnetism9-10, nanotube magnetism has not been fully understood. Besides experimental, the fundamental of the nanotube magnetism can be better understood by micromagnetic simulations11-13 and theoretical model14. Landeros et. al.15 and Escrig et.al.16 reported that there is a crossover between vortex and transverse modes in the magnetization process as the function of the nanotube wall thickness and radius by theoretically. In this work, we fabricated the NiFe nanotubes using electrodeposition method and the structural and magnetic properties are characterized. Micromagnetic simulations were carried out to understand the magnetization reversal behavior for single NiFe nanotube.
EXPERIMENTAL NiFe nanotubes with 80 nm inner diameter were growth by an array of pores templatedirected electrodeposition method with high filling rate and uniform growth. Commercially available anodized alumina (Anodisc from Whatman Inc) was used as template with 200 nm pore size and 60 µm thickness. One side of the template was sputtered with a seed layer of approximately 50 nm thickness copper to create conductive sidewalls. This thin layer covered only the pore walls of the template and leaving the orifices open. This leads to a pr
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