Electronic, magnetic and optical properties of MnPX$_3$ (X = S, Se) monolayers with and without chalcogen defects: A first-principle study

TL;DR

This study uses first-principle calculations to explore the electronic, magnetic, and optical properties of MnPX3 monolayers, revealing their stability, antiferromagnetic nature, and the effects of chalcogen vacancies on their properties.

Contribution

It provides a comprehensive first-principle analysis of MnPX3 monolayers, including stability, magnetic interactions, optical behavior, and defect effects, which were not previously detailed.

Findings

MnPX3 monolayers are stable and exfoliable from bulk.

They are Nél antiferromagnetic semiconductors with visible-range band gaps.

Chalcogen vacancies significantly alter electronic and magnetic properties.

Abstract

Based on density functional theory (DFT), we performed first-principle studies on the electronic structure, magnetic state and optical properties of two-dimensional (2D) transition-metal phosphorous trichalcogenide MnPX$_3$ (X=S and Se). The calculated interlayer cleavage energies of MnPX$_3$ monolayers indicate the energetic possibility to be exfoliated from bulk phase, with good dynamical stability confirmed by the absence of the imaginary contributions in the phonon spectra. MnPX$_3$ monolayers are both N\'eel antiferromagnetic (AFM) semiconductors with direct band gaps falling into the visible optical spectrum. Magnetic interaction parameters were extracted within the Heisenberg model to investigate the origin of the AFM state. Three in-plane magnetic exchange parameters play important role in the robust AFM configuration of Mn ions. The N\'eel temperatures ($T_\mathrm{N}$) were estimated by means of Monte Carlo simulations, obtaining the theoretical $T_\mathrm{N}$ of $103$\,K and $80$\,K for 2D MnPS$_3$ and MnPSe$_3$, respectively. With high spin state, Mn ions arranged in honeycomb lattices, the spin-degenerated band structures exhibit valley polarisation and was investigated in different biaxial in-plain strains, considering the spin-orbital coupling (SOC). 2D MnPX$_3$ monolayers show excellent performance on the optical properties, and the absorption spectra were discussed in detail to find the transition mechanism. Different amount and configuration of chalcogen vacancy were introduced into the MnPX$_3$ monolayers, and it is found that the electronic structures are heavily affected depending on the vacancy geometric structure, leading to different magnetic state and absorption spectra of defected MnPX$_3$ systems.