The coexistence of ferromagnetic (FM) state, out-of-plane piezoelectricity, and multiple channels for energy exchange in two-dimensional (2D) materials is highly advantageous for multifunctional ultrathin electronic devices. We predict the stable $\text{MoSe}X$ ($X$ = F, Cl, Br, I) semiconductor monolayers by first principles calculation. The ${\mathit{U}}_{\text{eff}}$ values of Mo atoms are obtained via linear fitting $\mathrm{GGA}+\left(\mathrm{U}\right)$ band gaps to match with HSE results. The magnetic configuration with the lowest energy is the FM state for the four monolayers. Among these monolayers, MoSeI exhibits the largest absolute value of out-of-plane piezoelectric strain coefficient ${\mathit{d}}_{31}$ (−0.55 pm/V). The absolute value is greater than those of the majority of 2D materials. Such as it is 4.2 times higher than ${\mathit{d}}_{31}$ of h-BN (0.13 pm/V) and 18.3 times higher than Janus TMD monolayers (0.03 pm/V). The ${\mathit{d}}_{31}$ of MoSeF and MoSeCl are 0.40 and 0.43 pm/V, respectively. Furthermore, there exists a positive correlation between the out-of-plane piezoelectric stress coefficient ${\mathit{e}}_{31}$ and the electronegativity difference ratio (${\mathit{r}}_{\text{ed}}$), which conforms to the electronegativity difference ratio effect. Intriguingly, MoSeF has multiple channels for energy exchange of holes and electrons in the bands due to the quasiequal extreme point defined in this work. This work presents four multifunctional monolayers that exhibit ferromagnetism, large out-of-plane piezoelectricity, and multiple energy exchange channels. It provides a possible approach for the design of multifunctional energy materials.

Close

PrevNext

View figure in article

• Dielectric properties
• Piezoelectricity
• Janus materials
• Monolayer films
• Piezoelectrics
• Semiconductor compounds
• Density functional calculations
• First-principles calculations