Predicted novel two-dimensional ferromagnetic VO2 with high Curie temperature and ferroelasticity

Abstract

Two-dimensional (2D) multiferroic materials with high-temperature intrinsic ferromagnetism and robust ferroelasticity are highly desirable for applications in future nanoelectronics, spintronics, and mechanical devices. Using density functional theory plus an evolutionary algorithm, we have predicted a novel 2D multiferroic VO₂ monolayer that can be exfoliated from bulk VO₂ and crystallize in an experimentally accessible monoclinic system (2/m). The proposed VO₂ monolayer shows higher energy stability with respect to those previously predicted, and exhibits dynamic, thermal, mechanical and ambient stabilities. The 2D VO₂ crystal is a ferromagnetic semiconductor with an indirect band gap of 1.33 eV and an estimated Curie temperature of 635 K. The 90° superexchange interaction is responsible for the high temperature ferromagnetic (FM) order. In addition, 2D VO₂ exhibits ferroelasticity with an energy barrier of 187.3 meV per atom and a reversible strain of 18.9%, allowing the regulation of the magnetic easy axis by external strain. Our principal findings corroborate the experimental observations and we look forward to further experimental verification.