Engineering multifunctional response in monolayer Fe3O4 via Zr adsorption: from half-metallicity to enhanced piezoelectricity

• Monolayer Fe 3 O 4 and Zr-adsorbed configurations investigated via spin-polarized DFT (GGA + U). • Zr adsorption introduces Fe–O–Zr hybrid states and site-dependent electronic transitions. • Top-site Zr induces localized mid-gap states; bridge-site causes full metallic behavior. • Zr adsorption enhances optical activity and increases piezoelectric coefficients up to 195 %. • Demonstrates a tunable route to engineer multifunctional 2D Fe 3 O 4 for spintronic applications. Two-dimensional (2D) magnetic oxides are increasingly studied for their multifunctional potential in fields like spintronics, optoelectronics, and energy conversion. In this research, we conduct a detailed first-principles study of pure monolayer Fe 3 O 4 and its modification through Zr adsorption at two sites: on top of an Fe atom and at the bridge between Fe atoms. Using spin-polarized density functional theory with the GGA + U method, we examine how adsorption affects structure, electronic, magnetic, optical, elastic, and piezoelectric properties. The original monolayer shows half-metallicity, strong spin polarization, and a moderate in-plane piezoelectric effect. Zr adsorption causes local lattice distortions and orbital hybridization, resulting in intermediate electronic states, a reduced bandgap, and increased optical absorption in both spin channels. Notably, Zr at the bridge site greatly enhances dielectric response, optical conductivity, and piezoelectric coefficients, tripling e 11 compared to the pristine layer. Elastic constants indicate mechanical softening after functionalization, and energy loss spectra display shifts in plasmon resonance. These findings suggest Zr adsorption offers a controllable, non-destructive way to tune spin, charge, and lattice interactions in Fe 3 O 4 monolayers, connecting magnetic, optical, and piezoelectric functionalities within a single 2D material platform.