Electric Polarization-Driven Modulation of Fe Adatoms on Ferroelectric $α$-In$_2$Se$_3$

The interplay among structural, electronic, and magnetic properties of Fe adatoms on the surface of two-dimensional ferroelectric α-In$_2$Se$_3$ is investigated using first-principles electronic structure calculations, with a focus on how these properties are modulated by the direction of the electric polarization of the substrate. We identify two competing adsorption sites for Fe adatoms, whose relative stability depends on the adatom concentration and can be reversed by switching the electric polarization of α-In$_2$Se$_3$. The calculated energy barrier for thermally activated hopping between these sites is approximately 0.4 eV, corresponding to a blocking temperature of around 100 K. The hybridization between Fe and In$_2$Se$_3$ orbitals strongly depends on the adsorption site and polarization direction, driven by variations in the local adatom geometry. As a result, the electronic configuration of adatom, magnetic moment, and magnetic anisotropy exhibit a pronounced site dependence and can be effectively modulated by switching the electric polarization of the In$_2$Se$_3$ layer. In particular, at higher adatom concentrations, an exceptionally large perpendicular magnetic anisotropy, exceeding 200 meV per Fe atom, emerges for one polarization direction, but is largely diminished when the polarization is reversed. These findings indicate that ferroelectric substrates offer a promising route for voltage-controlled tuning of magnetic adatom properties via reversible polarization switching.