Tunable Magnetic Order in Fe-Mg Codoped Montmorillonite Nanoclay Interfaced with Amino Acids

This study elucidates the sensitivity of the spin magnetic moment of the Fe-Mg codoped montmorillonite (MMT) nanoclay to its interactions with three unnatural amino acids (AAs): 5-aminovaleric acid, 2-aminopimelic acid, and DL-2-aminocaprylic acid, in the presence and absence of an aqueous environment. These AAs are known as intercalating agents for MMT clay, providing the formation of the nanoplates. Using spin-polarized density functional theory (SP-DFT), the magnetic moment and its tunability to the position of Fe and Mg impurities in the MMT nanoclay crystal lattice, along with the alignment of AA molecules on the nanoclay surface, have been investigated. There is substantial charge transfer between the AA molecule (a donor) and the MMT nanoclay (an acceptor), indicating their strong electrostatic interaction. Moreover, it is found that AA molecules stabilize Fe(II) and prevent its oxidation to Fe(III) through strong interactions with the nanoclay, highlighting the significance of clay-amino acid interactions. The calculations predict the possible transition in magnetic orders (ferromagnetic, antiferromagnetic, and ferrimagnetic) governed by interactions between the MMT nanoclay and the AA molecules in the vacuum and aqueous medium. The significant magnetic exchange coupling observed in some of the nanoclay models, in the presence of an aqueous medium, suggests a unique property of quantum ferrofluids. These findings indicate promising applications of these materials in biomedicine and bioengineering, particularly in the areas requiring an electromagnetic response, such as magnetic resonance and magneto-optical imaging, magnetic drug targeting, hyperthermia cancer treatment, magnetic separation, and magneto-mechanical sensors.