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.