Please cite this article in press as: F. Zhao, et al., Electrodeposition of Fe–Ga thin films from eutectic-based ionic liquid, Electrochim. Acta (2013), http://dx.doi.org/10.1016/j.electacta.2013.07.172 ARTICLE IN PRESS G Model EA-20965; No. of Pages 11 Electrochimica Acta xxx (2013) xxx–xxx Contents lists available at ScienceDirect Electrochimica Acta jo u r n al hom ep age: www.elsevier.com/locate/electacta Electrodeposition of Fe–Ga thin films from eutectic-based ionic liquid F. Zhao, S. Franz ∗ , A. Vicenzo 1 , M. Bestetti, F. Venturini, P.L. Cavallotti 1 Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta”, Politecnico di Milano, Via L. Mancinelli, 7, 20131 Milano, Italy a r t i c l e i n f o Article history: Received 30 March 2013 Received in revised form 24 July 2013 Accepted 24 July 2013 Available online xxx Keywords: Magnetostrictive material Fe–Ga thin film Electrodeposition Eutectic based ionic liquid Choline chloride a b s t r a c t In the present work, a novel process for Fe–Ga thin films electrodeposition is addressed and the mag- netic properties of the films are studied. The electrodeposition was carried out under ambient conditions using an ionic liquid electrolyte consisting of a mixture of choline chloride and ethylene glycol in the molar ratio 1:2, containing 0.3 M FeCl 2 and 0.1 M GaCl 3 , either in the absence or in the presence of oxalic acid at 4 or 17 mM concentration. The effect of oxalic acid on the discharge reaction of the single ionic species Fe 2+ and Ga 3+ and on their codeposition was investigated by linear sweep voltammetry, sug- gesting a specific action of oxalic acid on the cathodic reduction of Ga 3+ ionic species. Depending on deposition potential and oxalic acid concentration, alloy films with Ga content variable in the range up to about 20 at.% could be obtained. The Fe–Ga thin films showed a disordered body-cantered cubic phase (A2) with (1 1 0) preferred orientation and columnar microstructure, with a drastic change from pyramidal to granular surface morphology revealed raising the deposition potential. No superlattice reflections, indicating the formation of the D0 3 structure, were observed. A vibrating sample magnetome- ter was employed to measure hysteresis loops by applying longitudinal and transversal magnetic field on the Fe–Ga film plane. The saturation magnetization of as-deposited film reached 1.75 T for Fe 83 Ga 17 thin films, confirming that good quality films were obtained. For the same alloy composition, the coer- civity values were 67 Oe and 200 Oe, with applied field parallel and perpendicular to the film plane, respectively. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Owing to their good magnetostrictive and mechanical proper- ties, Fe–Ga alloys are considered a valid alternative to piezoelectrics or Terfenol-D for compact actuators and sensors to be operated in harsh and mechanical shock environments. Single-crystal Fe–Ga alloy with 17 at.% Ga shows a moderate magnetostriction (about 400 ppm) compared to Terfenol-D (about 2000 ppm). However, the bias field required is just about 100 Oe (10 times lower than Terfenol-D), and it can be achieved with a permanent magnet, making them suitable for compact devices. Furthermore, Fe–Ga alloys show tensile strength of about 500 MPa (20 times higher than Terfenol-D) [1] and a limited dependence of magnetostriction on the operating temperature in the range from -20 to 80 ◦ C [2]. Fe–Ga alloys with Ga content lower than 20 at.% are machinable, duc- tile, weldable and show good corrosion resistance [3]. Fe–Ga alloys show high crystalline anisotropy and the magnetoelastic behaviour changes with the crystallographic direction [4]. Textured polycrys- talline Fe–Ga alloys usually show lower magnetostriction (up to ∗ Corresponding author. Tel.: +39 0223993102. E-mail address: silvia.franz@polimi.it (S. Franz). 1 ISE member. 170 ppm) than the single crystals of similar composition, though are likely to be more commercially viable. Polycrystalline Fe–Ga films have been produced in the form of sheets, rods, ribbons and thin films. Fe–Ga thin films offer great advantages to the MEMS technology due to the possibility of downscaling without giving up robustness and sensitivity of the device. Compared to pure Fe, the addition of Ga greatly increases the magnetostriction of over 10-fold up to 400 ppm in single- crystalline alloy containing 17 at.% Ga [5]. The increase of magnetostriction over that of pure iron is attributed to the higher magnetoelastic coupling constant of the alloy due to short range ordering between Ga–Ga atoms in bcc -Fe with randomly substi- tuted Ga atoms (A2 structure) [6,7]. According to the phase diagram of the Fe–Ga binary system [8], the equilibrium solubility of Ga in -Fe is about 11 at.% at room temperature, and the solubility limit is 36 at.% at 1037 ◦ C. As much as 20 at.% Ga may be retained in metastable solid solution at room temperature [9]. At Ga content greater than 20 at.%, the bcc terminal solid solution phase evolves into ordered phases based on the B 2 , D0 3 , D0 19 and finally into the L1 2 structure at low temperature [10]. Magnetostriction in bulk Fe–Ga alloys was first discussed by Clark et al. [11] and has been studied by several groups [12–15]. Studies on bulk Fe–Ga alloys showed that in -phase Fe–Ga single crystal the maximum mag- netostriction occurs around ∼17 to 20 at.% Ga, depending on the cooling conditions, while a further increase in Ga content induces 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.07.172