Ferromagnetism in a semiconducting Janus NbSe hydride monolayer

Simultaneous control of charge and spin of electrons within a two-dimensional (2D) space is ideal for nanoscale spintronic applications, but a 2D material with both intrinsic magnetism and semiconducting nature has been rare. Here, we report a first-principles design of a semiconducting tetragonal NbSeH₂ monolayer with ferromagnetic order. The monolayer is made up of metal-ligand bonds on one-surface and hydrogen bridge bonds on the other surface, which forms a built-in electric polarization that opens a bandgap of 0.94 eV in an otherwise metallic system. As such, charge doping via an applied gate voltage not only enhances ferromagnetic coupling between local moments but also turns the monolayer into a half-metal that enables completely spin-polarized current. Monte Carlo simulations estimate a Curie temperature of 101 K at a hole-carrier density of 4.70 × 10¹³ cm⁻². Moreover, the monolayer shows high thermal and dynamic stability and can be extended to a large group of transition metals and chalcogens, pointing to a new ‘family' of Janus 2D materials for versatile applications.