Electronic structures and optical spectroscopies of 3d-transition metals-doped melanin for spintronic devices application

[Display omitted] •Magnetic and optical spectroscopies of melanin doped by 3d-TMS are investigated.•V/Fe-melanin have a half-metallic nature, and the other TMs-melanin are insulators.•The doping effect of TMs on melanin identifies the edge change of the optical spectra.•Emergence of ferromagnetism in melanin doped by 3d-TMs is useful for spintronics. By employing spin-polarized density functional theory calculations, systematic investigations are carried out on the electronic, magnetic and optical features of melanin doped with 3d-transition metals (TMs). Our study aims to seek for a novel appealing nanomaterial that could be applied to spintronic devices. The structural models of isolated monomers of melanin and the electronic spin-polarized properties of these organic molecules doped with 3d-TMs are analyzed. According to our theoretical finding, the Ni-doped melanin has a nonmagnetic state, although a tiny magnetic moment is induced in both Cu- and Zn-doped into melanin. This can be essentially ascribed by the bonding interactions between these 3d-TMs and oxygen atom. Interestingly, the remaining frameworks of isolated monomer structures of melanin doped with 3d-TMs carry a quite significant magnetic moment. Only V- and Fe-doped into melanin are found to exhibit a half-metallic character, albeit the other TMs-melanin have a semiconducting property. For the overall systems, such as the pure melanin and its doping with 3d-TMs, we computed the optical absorption, reflectivity, and X-ray absorption near-K-edge structure spectra to identify the edge alteration of the optical spectra. This scrutiny could pave a new route to acquire the ferromagnetism in the isolated monomers of melanin doped with some selected 3d-TM species. We anticipate that these organic molecules doped with 3d-TMs could be potential candidates for energy storage, catalysts, and molecular electronic and spintronics.