Ferroelectrically controlled electromagnetic and transport properties of VN2H2/Al2O3 van der Waals multiferroic heterostructures

Abstract

The vertical integration of a ferromagnetic monolayer and a ferroelectric monolayer into van der Waals heterostructures offers a promising route to achieve two-dimensional multiferroic semiconductors owing to the lack of intrinsic single-phase multiferroic materials in nature. In this study, we propose a VN₂H₂/Al₂O₃ van der Waals magnetoelectric multiferroic heterostructure and investigate its electronic, magnetic, and transport properties using density functional theory combined with the Boltzmann transport theory. The VN₂H₂ monolayer is a room-temperature ferromagnetic semiconductor with a band gap of 0.24 eV and a Curie temperature of 411 K, while the Al₂O₃ monolayer is a ferroelectric semiconductor with a polarization value of 0.11 C m⁻². In the VN₂H₂/Al₂O₃ van der Waals heterostructures, the conversion between the metal and the semiconductor can be controlled by altering the polarization of the Al₂O₃ layer. The VN₂H₂/Al₂O₃ van der Waals heterostructure retains room-temperature ferromagnetism, and the reverse of polarization is accompanied with a change in the direction of the easy magnetization axis. In addition, electrostatic doping can significantly improve the conductivity of the downward polarization state and transform the upward polarization state from a metal to a half-metal, achieving 100% spin polarization. Our results thus pave the way for achieving highly tunable electromagnetic and transport properties in van der Waals magnetoelectric heterostructures, which have potential applications in next-generation low-power logic and memory devices.