Electrodeposition of Magnetic Cobalt Thin Films and Nanowires from Ethylene Glycol-Based Solutions
Authors: Panzeri Gabriele , Accogli Alessandra , Gibertini Eugenio , Cuneo Federico , Magagnin Luca 
Published: February 2020

Cobalt and cobalt alloys are known for a large variety of industrial applications especially in microelectronics because of their magnetic properties. In fact, the possibility to obtain hard magnetic Co-alloys is of a great interest for magnetic recording. Cobalt electrodeposition have been extensively studied from aqueous solutions and only in a few cases from non-aqueous ones. Since the formation of cobalt oxides/hydroxides, strongly connected to the pH variation at the working electrode surface during deposition, has to be avoided in order to obtain a good magnetic film, the employment of organic solutions may be a suitable alternative to the stardard plating bath. Nowadays, particular attention is given to deep eutectic solvents (DESs) because of their easy preparation procedure and working conditions [1, 2, 3]. In this work, we tried to simplify further this kind of solutions by studying the electrodeposition of Co from ethylene glycol solvent without the employment of any quaternary ammonium salt; it has to be noted that only a few studies on this system are reported in literature [4, 5, 6]. Electrochemical characterization was performed in terms of cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Microstructural, morphological and magnetic characterization were performed on metallic deposits, obtained by means of potentiostatic electrodepositions carried out from -0.85 V vs Pt to -0.95 V vs Pt at 70° C. The films obtained were compact and showed a high purity; no oxygen was detected by EDX analysis. X-Ray diffraction (XRD) pattern showed the material to have an hexagonal microstructure. Vibrating sample magnetometer (VSM) was used to assess the magnetic properties of the films, resulting to have soft magnetic properties (80 Oe). In addition, commercially available alumina membranes were employed for the synthesis of nanowires with enhanced magnetic properties (>200 Oe). Annealing at 600° C for 3h was carried out to promote crystal growth; microstructural and magnetic characterization were carried out before and after heat treatment, showing a slight increase in the film coercivity.

References

[1] Welton T. Room-temperature ionic liquids. Solvents for synthesis and catalysis. Chemical reviews. 1999 Aug 11;99(8):2071-84.
[2] Abbott AP, Boothby D, Capper G, Davies DL, Rasheed RK. Deep eutectic solvents formed between choline chloride and carboxylic acids: versatile alternatives to ionic liquids. Journal of the American Chemical Society. 2004 Jul 28;126(29):9142-7.
[3] Li M, Wang Z, Reddy RG. Cobalt electrodeposition using urea and choline chloride. Electrochimica Acta. 2014 Jan 23;123:325-331.
[4] Vorobyova TN, Vrublevskaya ON. Electrochemical deposition of gold–tin alloy from ethylene glycol electrolyte. Surface and Coatings Technology. 2010 Jan 15;204(8):1314-8.
[5] Nguyen HP, Wu M, Su J, Vullers RJ, Vereecken PM, Fransaer J. Electrodeposition of bismuth telluride thermoelectric films from a nonaqueous electrolyte using ethylene glycol. Electrochimica Acta. 2012 Apr 30;68:9-17.
[6] Neuróhr K, Pogány L, Tóth BG, Révész Á, Bakonyi I, Péter L. Electrodeposition of Ni from various non-aqueous media: the case of alcoholic solutions. Journal of The Electrochemical Society. 2015 Jan 1;162(7):D256-64.