Pulse electrodeposition and electrochemical quartz crystal microbalance techniques for high perpendicular magnetic anisotropy cobalt nanowire arrays

Abstract

This research is focused on the development of pulse electrodeposition techniques to fabricate a high-density array of vertically oriented, high-magnetic anisotropy cobalt nanowires using a porous polymer film template. This type of array is a competitive candidate for future perpendicular magnetic media capable of storage densities exceeding 1Terabit∕in.2 The polymer template, derived from a self-assembling P(S-b-MMA) diblock copolymer film, provides precise control over the nanowire diameter (15nm) and interwire spacing (24nm), whereas nanowire length (typically 50to1000nm) is controlled accurately with the aid of real-time electrochemical quartz crystal monitoring. Pulse and pulse-reversed electrodeposition techniques, as compared to dc, are shown to significantly enhance the perpendicular magnetic anisotropy of the magnetic nanowire array and ultimately result in coercivity as large as 2.7kOe at 300K. Magnetic and structural characterizations suggest that these properties arise from an improved degree of magnetocrystalline anisotropy (due to c-axis oriented crystal growth and improvements in crystal quality) that strongly supplements the basic shape anisotropy of the nanowires. Low temperature magnetometry is used to investigate exchange bias effects due to the incorporation of CoO antiferromagnetic impurities during the electrodeposition process and subsequent Co oxidation in air.