Electronic and Magnetic Properties of Lanthanide-Substituted Two-Dimensional Monolayer GdI ₃ by Strain Engineering: Insights from First-Principles Investigation

Here we demonstrate a systematic first-principles prediction of the electronic structure and magnetic properties of lanthanide (rare-earth)-substituted gadolinium iodide GdI₃ monolayers, i.e., <i>Ln</i>GdI₆ (<i>Ln</i> = La, Nd-Eu, and Tb-Yb). The <i>Ln</i>GdI₆ family with an antiferromagnetic (AFM) ground state exhibits good thermal and dynamical stability, and the relatively low cleavage energy suggests that such an iodide monolayer can feasibly be experimentally prepared. It is noteworthy that 4f-electron substitution can significantly enhance the magnetic anisotropy. In particular, five members of the <i>Ln</i>GdI₆ (<i>Ln</i> = La, Tb, Dy, Ho, and Er) family display perpendicular magnetic anisotropy character. Furthermore, the magnetic moment and band gap of four representative <i>Ln</i>GdI₆ (<i>Ln</i> = Nd, Sm, Dy, and Yb) systems can be effectively modulated by applying a wide array of biaxial strain. The SmGdI₆ system transforms into a half-semiconductor with a ferromagnetic (FM) ground state under a tensile strain of 6%, while NdGdI₆ and DyGdI₆ members exhibit magnetically stable AFM semiconductor character across the whole applied strain range. Moreover, the YbGdI₆ monolayer exhibits metallic behavior under compressive strain. This work presents a brand new mixed-lanthanide family aiming to broaden the diversity of f-electron-based two-dimensional magnets and highlights strain as a powerful tool for tuning the electronic and magnetic properties of rare-earth trihalides, which are expectantly regarded as promising candidates for high-density spintronics applications.