Ferroelectric control of magnetic coupling in a Cr dimer adsorbed on $α$-In$_2$Se$_3$

Abstract

Ferroelectric substrates offer a route to controlling magnetic interactions in low-dimensional systems through polarization-dependent changes in local bonding and electronic structure. Here, using first-principles calculations, we investigate the adsorption of 3$d$ transition-metal atoms and dimers on monolayer $α$-In$_2$Se$_3$ and identify Cr as a stable dimer configuration on both polar surfaces. Reversing the ferroelectric polarization drives a pronounced change in its magnetic coupling: the AFM state is favored for one polarization, whereas the FM and AFM configurations become nearly degenerate for the opposite one. Analysis of the spin density, projected electronic states, and Wannier Hamiltonians reveals concomitant changes in the direct Cr-Cr hopping and in the interaction with the bridging Se atom. In particular, enhanced Cr-Se hybridization and Se spin polarization, together with a strong reduction of the direct two-center Cr-Cr hopping, point to a polarization-dependent balance between direct and substrate-mediated exchange contributions. These results show how ferroelectric polarization can tune magnetic interactions in an atomically defined 2D hybrid system.