Please cite this article in press as: A. Ramazani, et al., Fabrication of high aspect ratio Co nanowires with controlled magnetization direction using ac and pulse electrodeposition, Mater. Chem. Phys. (2008), doi:10.1016/j.matchemphys.2008.05.050 ARTICLE IN PRESS G Model MAC-12510; No. of Pages 5 Materials Chemistry and Physics xxx (2008) xxx–xxx Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Fabrication of high aspect ratio Co nanowires with controlled magnetization direction using ac and pulse electrodeposition A. Ramazani ∗ , M. Almasi Kashi, M. Alikhani, S. Erfanifam Department of Physics, University of Kashan, Ghotb Boulevard, Kashan 78317-51167, Iran article info Article history: Received 20 February 2008 Received in revised form 29 April 2008 Accepted 23 May 2008 PACS: 75.30.GW 75.60.Ej 75.75.+a Keywords: ac electrodeposition Pulse electrodepsition Porous anodic aluminum oxide abstract High aspect ratio cobalt nanowire arrays were fabricated using ac and pulse electrodeposition techniques into the porous alumina templates. The pH was adjusted to be about 4. The effects of electrodeposition time in both the ac and pulse techniques were investigated. Using ac electrodeposition technique, increasing the deposition time significantly decreased the coercivity and squareness. The coercivity and squareness of about 600Oe and 0.35 were obtained for high aspect ratio Co nanowires, respectively. In the pulse electrodeposition technique, increasing the off-time between the pulses stabilizes the microstructure thereby suppresses the reduction of the coercivity and squareness. A coercivity of about 1400 Oe was seen for high aspect ratio Co nanowires electrodeposited with 200 ms off-time and different pulse numbers. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Recently, fabrication of nanowire arrays, especially magnetic nanowire arrays, has become the subject of intensive study [1–4] due to their potential applications in the high-density magnetic storage [5]. The magnetic behaviour of such systems is mainly dependent on the shape and magnetocrystalline anisotropy along with magnetostatic interaction among magnetic wires [6,7]. The structure of magnetic nanowires can be controlled by adjusting deposition parameters [8]. It is expected that in the case of long nanowires, the preferred magnetization direction of the array is dominated by the strong nanowire shape anisotropy, and conse- quently the easy axis is expected to lie along the nanowire axis. In contrast, some experimental results have shown that the pre- ferred magnetization direction of such systems becomes transverse to the nanowire [9]. Co nanowires were much more interested by its large crystal anisotropy when it is in the hcp structure. It is shown that the electrodeposition of Co nanowires leads to a polycrystalline structure [10,11]. The effects of AAO pore diameter, current density, pH, annealing and deposition under external magnetic fields on the structure and magnetic properties of the nanowire arrays were also studied [12,13]. The effect of substrates on the microstructure and magnetic properties of electrodeposited Co nanowire arrays in ∗ Corresponding author. Tel.: +98 3615553646; fax: +98 3615552935. E-mail address: rmzn@kashanu.ac.ir (A. Ramazani). porous anodic aluminum oxide membrane was also investigated [14]. In our previous works Co nanowire arrays embedded in porous alumina were studied [15,16]. In our first work on the Co nanowires the effect of ac electrodeposition frequency and waveform on the magnetic properties and microstructures of Co nanowires were investigated [15]. Overthere, the Co nanowires with almost 2 m length were electrodeposited at the bottom of pores with 20 m length, using an electrolyte with pH of 4. The coercivity was varied from almost 1000 Oe to 2000 Oe using different conditions. In our second work on the Co nanowires [16], initially the effect of the frequency and waveform were investigated using ac electrodeposi- tion in pH of 6. High pH value and low diffusion path were seen to induce a high growth rate; therefore, frequency and waveform have not shown significant effect on the coercivity. The pulse electrode- position technique was then employed and a coercivity of 2300 Oe was obtained at optimum conditions. In this work, the ac and pulse electrodeposition method were employed to fabricate high aspect ratio Co nanowires. The aim of this research was to investigate the stability of crystal growth in both the ac and pulse techniques for short- and long- electrodeposition time. 2. Experiments The high purity aluminum foil (99.999%) was annealed at 500 ◦ C in the air for 2 h and etched in 1 M NaOH for 3 min. The sample 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.05.050