Janus S-XSSe: A new family of 2D polar half-metals with stacking-engineered magnetism and antiferromagnetic spin splitting

Abstract

The quest for materials uniting polarity with metallicity or half-metallicity is pivotal for next-generation multifunctional devices, yet their realization, particularly with robust magnetism, remains a formidable challenge. Here, we unveil a new family of two-dimensional (2D) Janus S-XSSe (X = Re, Os, V, Cr, Mo) monolayers with quasi-square lattice as intrinsically polar metals/half-metals, exhibiting substantial out-of-plane polarization (2.56-4.00 pC/m) and excel-lent structural stability. We demonstrate that S-VSSe, S-CrSSe, and S-MoSSe are polar half-metals, where the distinct origins of polarity (S-Se electronegativity difference) and half-metallicity (transition metal d-orbitals) enable their robust coexistence. Furthermore, we identify a viable polarization switching pathway, whose energy barrier can be effectively tuned by biaxial strain. Moreover, bilayer S-XSSe systems exhibit rich, stacking-dependent magnetism, elucidated via spin Hamiltonian analysis and interlayer electron hopping. Remarkably, an interlayer antiferromagnetic S-VSSe bilayer with parallel polar stacking develops significant spin splitting, a direct consequence of the built-in electric field breaking inversion symmetry. This discovery of a novel class of polar metals/half-metals, particularly the emergent antiferromagnetic spintronic phenomena in bilayers, paves the way for innovative spintronic and multifunctional electronic applications.