Strong spin-phonon coupling in two-dimensional monolayer VS2 and the origin of its high-temperature magnetism

Abstract

Exploring intrinsic two-dimensional (2D) ferromagnetic (FM) semiconductors with high Curie temperatures (T c) is an ongoing challenge. Herein, we found that the phonons of monolayer H-VS2 are strongly coupled to the magnetic ordering with the spin-phonon coupling constants (15.80 cm−1 for A1g and 78.72 cm−1 for E2g1 ) an order of magnitude larger than most other 2D materials, which restricts structural reconstruction of FM ground state through spin interactions. Based on anharmonic model, the variation trend of phonon energy with temperature clearly demonstrates FM ground state at room temperature. The theoretically predicted high T c of 303 K, closely in line with experimental observations, is correlated to the three lowest d-orbitals (i.e. dxy , dz2 and dx2−y2 ) split by the unique crystal field. The proximity of their energy levels facilitates efficient mutual virtual exchanges, which greatly prompts superexchange-driven FM coupling of adjacent spins, as confirmed by their orbital-resolved magnetic exchange coefficients. Our work validates the double-orbital model for the magnetic coupling mechanisms in 2D H-VS2, offers potentials to create novel high T c spintronic semiconductors and paves a way for design of complex micro/nano-magnetoelectric devices.