Electrodeposition of Soft Magnetic Fe-Co and Fe-Co-Mn Films from Deep Eutectic Solvents

Abstract

While electrodeposited magnetic alloys have been used for decades in hard disc drives and other micro-electro-mechanical systems (MEMS), these alloys have evolved many times for improvement in magnetic properties such as low coercivity and high magnetic moment[1, 2]. Despite their wide industrial use, there is still a desire and opportunity to further improve the properties of such materials[3]. Electrodeposition has been the preferred fabrication method for such soft magnetic films due to its several advantages such as low cost, fast deposition rate, easy scaling, flexibility of substrate geometry, and simplicity of film anisotropy control[4]. In the past several years, room temperature ionic liquids, the current generation also being known as deep eutectic solvents (DES), have become an attractive alternative to traditional aqueous deposition baths. These solvents avoid the hydrogen generation that often reduces deposit quality and efficiency in aqueous baths. It therefore provides some opportunities to tune the magnetic properties of deposited materials by incorporating additional elements with more negative deposition potentials than are viable in aqueous baths, for example Mn[5]. Despite significant progress in literature on the electrodeposition of various material from DESs, their suitability for depositing magnetic films is relatively little-studied[6]. This work studies the magnetic characteristics of FeCo alloys electrodeposited from the DES formed of a 1:2 mole ratio of choline chloride and urea (ChCl-U). In addition, a tertiary FeCoMn film has been electrodeposited from ChCl-U, and its magnetic properties have been studied. Both FeCo and FeCoMn films electrodeposited from a variety of conditions have been shown by VSM measurements to be ferromagnetic, and saturation magnetization and coercivities have been extracted from hysteresis loops (Fig. 1). The incorporation of small amounts of Mn (~2%) has been predicted to slightly improve the magnetization of FeCo films, however larger amounts dilute the ferromagnetic coupling within the film. Coercivities on the order of a few hundred Oersteds are observed. The film morphology is found to be relatively smooth for thin deposits, however cauliflower-like film growth is observed after long deposition times. Films contain micro-scale cracks in most cases. The detailed results on electrodeposition, x-ray diffraction, as well as other characterizations will be discussed.