Electrodeposition of nanocrystalline Fe_XCo_1-X thin films from choline chloride-urea deep eutectic solvents

Fe_xCo_1-x thin films were electrodeposited from a choline-urea deep eutectic solvent (DES) containing Fe³⁺ and Co²⁺ ions under ambient conditions. Anomalous co-deposition was observed, with Fe preferentially depositing over Co. With higher cathodic potential, the film's morphology shifted from smooth to nodular. X-ray diffraction (XRD) analysis showed iron oxide impurities at lower overpotential and temperatures (e.g., <-0.9 V at 70 °C), while impurity-free, nanocrystalline Co₅₀Fe₅₀ films had formed at higher temperatures (e.g., 130 °C). The films exhibited a body-centered cubic (BCC) structure with (110) preferred orientation and grain sizes of 30 nm-40 nm.