Structural, optical, and magnetic tuning in Fe–Li/Cu multilayer thin films via controlled electrodeposition

This study presents the fabrication and in-depth analysis of Fe–Li multilayer thin films electrodeposited on Cu substrates, emphasizing the effect of varying Li concentrations (0.1–0.5 M) on their structural, optical, and magnetic characteristics. The multilayers were produced using a sequential electrodeposition process followed by thermal annealing at 300°C. X-ray diffraction (XRD) analysis confirmed the development of a cubic polycrystalline phase, with crystallinity improving as Li concentration increased. UV–Vis spectroscopy exhibited strong absorption within the visible region and a tunable optical band gap (1.02–1.21 eV), resulting from morphological alterations induced by Li incorporation. Scanning electron microscopy (SEM) images revealed compact, nanograined surfaces with uniform coverage across the substrate. Vibrating sample magnetometry (VSM) measurements indicated a significant dependence of magnetic behaviour on Li concentration: films with 0.1–0.3 M Li displayed ferromagnetic ordering with progressive enhancement in saturation magnetization, whereas the 0.4 M film showed magnetic suppression due to structural disorder. Interestingly, at 0.5 M Li, the films exhibited a sharp recovery in magnetization and a high squareness ratio, implying the onset of superparamagnetic-like behavior. Overall, the results demonstrate that Li incorporation effectively tunes the magneto-optical characteristics of Fe–Li/Cu multilayers, making them strong contenders for use in spintronic devices, magnetic sensors, and thin-film energy systems.