Exchange Engineering of a Two-Dimensional Half-Metal.

We report the emergence of two-dimensional itinerant half-metallicity in a two-atomic-layer thick iron-palladium alloy. Against the common belief that spin-orbit coupling is adverse to half-metallicity, the complex interplay between exchange and spin-orbit coupling counterintuitively enables it via electronic band hybridization. The 2D ferromagnet is engineered directly via controlled alloying and is verified experimentally via spin-resolved band structure analyses. First-principles calculations corroborate its tunability by providing a systematic bottom-up approach through stepwise ground-state construction. The appearance of hybridization points at specific k points, via interplay between exchange and spin-orbit interactions, is responsible for the emergence of half-metallicity.