Large Out-of-Plane Piezoelectric Effect in Janus Ferromagnetic Semiconductor Monolayer of CrOFBr

TL;DR

This study reveals that Janus CrOFBr monolayer exhibits significant out-of-plane piezoelectricity and ferromagnetism, with strain-tunable responses surpassing many 2D materials, promising for nanoelectronics and spintronics.

Contribution

First-principles calculations demonstrate that Janus CrOFBr monolayer has intrinsic ferromagnetic semiconducting behavior with large, strain-enhanced out-of-plane piezoelectric effects, advancing 2D multifunctional material design.

Findings

Out-of-plane piezoelectric coefficients up to 1.21 and 0.63 pm/V.

Tensile strain increases piezoelectric response by 27% and 67%.

Piezoelectric response correlates with electronegativity difference.

Abstract

The exploitation of piezoelectric ferromagnetism (PFM) in two-dimensional (2D) materials with large out-of-plane piezoelectric response is motivated not only by technological applications but also scientific interest. In this study, the CrONM monolayer family (N=F, Cl; M=Br, Cl) was investigated using first-principles calculations, revealing that the Janus CrOFBr monolayer exhibits intrinsic ferromagnetic semiconductor behavior along with a significant out-of-plane piezoelectric effect. The calculated out-of-plane piezoelectric strain coefficients d$_{31}$ and d$_{32}$ are up to 1.21 and 0.63 pm/V, respectively. These values are greater than those of the majority of 2D materials. Furthermore, our findings demonstrate that applying tensile strain can enhance the out-of-plane piezoelectric response, leading to a respective 27% and 67% augmentation in the piezoelectric strain coefficients d$_{31}$ and d$_{32}$ compared to the unstrained configurations. This discovery holds great potential for propelling the field of nanoelectronics forward and facilitating the development of multifunctional semiconductor spintronic applications. Finally, by comparing d$_{31}$ and d$_{32}$ of the CrONM monolayer family (N=F, Cl; M=Br, Cl), we find that the magnitudes of d$_{31}$ and d$_{32}$ are correlated with the electronegativity difference between the M and N atoms. These findings provide valuable insights for the design of 2D piezoelectric materials with enhanced vertical piezoelectric responses.