Ab initio design of 2D spintronic materials: engineering magnetism and ferroelectricity through defects and doping

Two-dimensional (2D) materials and their van der Waals (vdW) heterostructures offer unprecedented opportunities for engineering magnetic and ferroelectric properties at the atomic scale. Reduced dimensionality enhances interlayer interactions, symmetry breaking, and spin-orbit coupling (SOC), making these systems promising platforms for next-generation spintronic and multiferroic devices. Achieving robust and tunable ferroic behavior in the 2D limit requires a microscopic understanding of how defects, interlayer structure, charge redistribution, and carrier doping influence magnetic and ferroelectric responses. This thesis investigates the key mechanisms governing magnetism and ferroelectricity in representative 2D materials and heterostructures, using first-principles density functional theory (DFT) calculations to examine atomic-scale effects such as Gr defects and Fe clustering in Fe/Gr/Co stacks, interlayer sliding and charge redistribution in bilayer VTe2, and spin–orbit-driven magnetic anisotropy in hole-doped monolayer VS2, thereby identifying principles for tailoring ferroic properties in ultrathin systems. In Fe/Gr/Co synthetic antiferromagnets (SAFs), graphene (Gr) vacancy defects and Fe clustering modulate the interlayer magnetic coupling. Motivated by experimental observations, DFT calculations show that these structural features weaken antiferromagnetic (AFM) superexchange and promote ferromagnetic (FM) alignment. Spectromicroscopy measurements at the Nanospectroscopy and VUV beamlines at Elettra confirm these effects, and both theory and experiment demonstrate that passivating defect sites with Ag atoms or carbon-based molecules restores AFM coupling. In metallic bilayer VTe2, sliding-induced ferroelectricity arises from charge redistribution across the vdW gap during interlayer sliding, breaking inversion symmetry. The out-of-plane (OOP) polarization depends sensitively on interlayer spacing, Te corrugation, magnetic configuration, and external perturbations such as strain, Janus substitution, and point defects, which can selectively enhance or suppress the polarization. In hole-doped monolayer VS2, the switch from in-plane (IP) to OOP magnetization is driven by larger spin–orbit–induced splittings and energy shifts that favor the perpendicular orientation. Hole doping depletes the higher-energy valence states most affected by these splittings, lowering the energy more strongly for the OOP configuration and enabling perpendicular magnetic anisotropy at realistic doping levels. This mechanism provides general strategies for tuning magnetic anisotropy in 2D semiconductors. Collectively, these studies reveal how interlayer coupling, defect chemistry, charge redistribution, and spin–orbit interactions govern ferroic responses in 2D materials. The results provide a unified microscopic framework and actionable strategies for engineering magnetic and ferroelectric functionalities in ultrathin systems, advancing the design of energy-efficient, multifunctional spintronic and multiferroic devices.