First-principles prediction of polar half-metallicity and out-of-plane piezoelectricity in two-dimensional quintuple layered cobalt selenide

Abstract

Polar half-metals, possessing both polarity and half-metallicity, may have potential as media in novel spintronic quantum devices, but they have never been reported in the two-dimensional (2D) form. By combining the particle swarm optimization with first-principles calculations, we predict a stable 2D polar half-metal, quintuple layered Co₂Se₃ monolayer. This is an XY magnet where its magnetism is governed by the interplay between super and double exchange along the Co–Se–Co motifs. Notably, 2D Co₂Se₃ also exhibits out-of-plane piezoelectricity. We have, thus, discovered a multiferroic 2D compound with robust half-metallicity, rendering it great potential in advanced multiferroic applications.