Two-dimensional multiferroicity and half-metallicity of the carrier-doped 2H-VSiN3 monolayer

Abstract

Two-dimensional (2D) multiferroics is a burgeoning field in condensed matter physics and materials science. Current investigations to achieve multiferroicity are mainly based on 2D ferromagnetic materials and their van der Waals structures. In this work, we propose a feasible route for achieving 2D multiferroicity in a nonmagnetic 2H-VSiN₃ monolayer. Owing to its intrinsic Janus structure, 2H-VSiN₃ possesses a spontaneous electric polarization of 7.98 pC m⁻¹, which is comparable to that of other well-known 2D ferroelectric materials. Remarkably, ferroelectric polarization is controllable and sign switchable when an external electric field is applied. In terms of the Stoner mechanism (N(E_F)I_S > 1), p- and d-orbital ferromagnetisms are achieved by hole and electron doping, respectively, benefiting from the peculiar sombrero-type band edge and van Hove singularity in the electronic density of states. At the mean field level, the highest Curie transition temperature is estimated to be 823 K. Furthermore, a semiconductor to half-metal transition driven by carrier doping is revealed, in which the half-metallic feature depended on the type of carrier. Owing to the breaking of the time reversal symmetry, carrier doping led to a spontaneous valley polarization of 42 meV, whose sign was switchable by changing the type of carrier. The Hamiltonian model analysis further demonstrated that valley polarization can occur only at the bottom of the conduction band. Finally, we elucidated that introducing p- and n-type dopants is a general route to achieve magnetic transition in 2D van Hove materials. Our results demonstrate the coexistence of ferroelectricity, ferromagnetism, ferrovalley, and half-metallicity in a carrier-doped nonmagnetic 2D material and provide a feasible way to achieve gating control of multiferroicity.