Strain Controlled Magnetic and Optical Properties of Monolayer 2H-TaSe$_2$

TL;DR

This study uses first-principles calculations to explore how mechanical strain influences the magnetic and optical properties of monolayer 2H-TaSe$_2$, revealing strain-induced ferromagnetism and phonon mode modifications.

Contribution

It demonstrates the strain-dependent magnetic and optical behavior of monolayer 2H-TaSe$_2$, including the emergence of ferromagnetism and phonon mode degeneracy lifting, providing insights for nanoelectronic applications.

Findings

Ferromagnetism appears under uniaxial tensile strain.

Strain lifts Raman-active phonon degeneracy.

Magnetic order remains stable under additional z-axis compression.

Abstract

First-principles calculations are used to probe the effects of mechanical strain on the magnetic and optical properties of monolayer (ML) 2H-TaSe$_2$. A complex dependence of these physical properties on strain results in unexpected behavior, such as ferromagnetism under uniaxial, in-plane, tensile strain and a lifting of the Raman-active E' phonon degeneracy. While ferromagnetism is observed under compression along x-axis and expansion along y-axis, no magnetic order occurs when interchanging the strain direction. The calculations show that the magnetic behavior of the system depends on the exchange within the 5d orbitals of the Ta atoms. The magnetic moment per Ta atom persists even when an additional compressive strain along the z-axis is added to a biaxially-strained ML, which suggests stability of the magnetic order. Exploring the effects of this mechanical strain on the Raman-active phonon modes, we find that the E$^"$ and E' modes are red-shifted due to Ta-Se bond elongation, and that strain lifts the E' mode degeneracy, except for the symmetrical biaxial tensile case. Our results demonstrate the possibility of tuning the properties of 2D-materials for nanoelectronic applications through strain.