A first-principles study on antiferromagnetic VYNF2 with flat robust bands, valley splitting, and an out-of-plane piezoelectric response

Abstract

Antiferromagnetic materials without a stray field are highly desired for future spintronics. Based on first-principles studies, we have found that the magnetic order of the chemically modified functionalized Janus MXene VYNF₂ becomes antiferromagnetic, compared to the ferromagnetic order of the pristine MXene VYN. Chemical modification enhances not only the structural but also magnetic stability under thermal fluctuation. The asymmetric charge and chemical bonds induce an inherent field, leading to a sizable out-of-plane piezoelectric response in VYNF₂. There is valley splitting in the top valence band between the K and −K points, which is derived via perturbation theory. Strain effects on the magnetic critical temperature, band gap, and piezoelectric response are also studied for VYNF₂, indicating that the band gap is robust against strain. We suspect VYNF₂ can be designed for an antiferromagnetic spin-valley gate in nanoscale spintronics with a piezoelectric response.