Synthesis, characterization, and magnetic properties of FeCoNi ternary alloy nanowire arrays
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Craig A. Grimesa) Department of Materials Science and Engineering, and Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, 16802 (Received 16 August 2004; accepted 28 September 2004)
FeCoNi ternary alloy nanowire arrays 32–106 nm in diameter were fabricated within nanoporous alumina membranes using 15 Vrms alternating current electrodeposition at frequencies of 50, 250, 500, 750, and 1000 Hz. The magnetic coercivity and hysteresis loop squareness-ratio (Mr/Ms) were studied as functions of electrolyte composition, nanowire diameter, and nanowire aspect ratio.
I. INTRODUCTION
Fabrication of magnetic nanowires currently is of significant interest due to their potential for use as magnetic data storage devices,1,2 as well as magnetic-field or acoustic sensors.3 In combination with a suitable template, electrodeposition is an excellent and relatively low-cost method for fabrication of magnetic nanowires. An advantage of the electrodeposition process is the relative ease with which the resulting alloy composition can be controlled, through various process parameters such as electrolyte composition, bath pH, and mode of deposition [direct current (dc), pulsed, and alternating current (ac)]. There are reports in the literature in which nanowires have been made of elemental Fe, Co, and Ni metals, and in various binary alloy combinations.4–8 For example Whitney et al.4 have fabricated Co and Ni nanowires using potentiostatic dc electrodeposition. Paulus and co-workers5 fabricated Fe, Co, and Ni nanowires using ac electrodeposition at 16 Vrms 50 Hz. Fodor et al.6 synthesized Co1−xFex nanowires using ac electrodeposition at 8 V at 60 Hz with different electrolyte concentrations used to obtain various compositions. Zhu et al.7 used constant current dc deposition to fabricate Co67Ni33 nanowires. Khan and Petriowski8 used 14 V, 60 Hz electrodeposition to fabricate Fe26Ni74 nanowires. Ternary alloys of Fe–Co–Ni have been found to possess excellent magnetically soft properties,9–11 including relatively high values of saturation magnetization and extremely low coercivities, making them ideal for
II. EXPERIMENTAL DETAILS
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0476 J. Mater. Res., Vol. 19, No. 12, Dec 2004
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applications including electromechanical devices. 9 Therefore we are motivated to fabricate and characterize the magnetic properties of Fe–Co–Ni alloy nanowire arrays; to the best of our knowledge, there are no reports in the literature on such nanowires. Fabrication of the nanowire arrays using electrodeposition requires a highly ordered template of predetermined channel length, width, and density. If material is deposited into the pores, nanowires with a diameter determined by the pore diameter can be fabricated. It is well known that anodization of aluminum in acidic electrolytes leads to a nanoporous alumina membrane,12 which serves as an excellent template for subsequent nanowire fa
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