The Piezoelectricity and Doping‐Induced Ferromagnetism of Janus XYP₂ (X/Y = Si, Ge, Sn, and Pb; X ≠ Y) Monolayers

2D materials that possess multifunctional properties are of great interest for applications in semiconducting devices. Herein, a series of novel Janus XYP 2 (X/Y = Si, Ge, Sn, and Pb; X ≠ Y) monolayers with good stability, electronic, mechanical, piezoelectric properties, as well as ferromagnetic properties are predicted based on density functional theory. They are all indirect‐bandgap semiconductors with bandgaps varying from 0.56 to 2.18 eV. The monolayers exhibit in‐plane and out‐of‐plane piezoelectricity with large piezoelectric coefficients, suggesting that they are promising piezoelectric materials for nanoelectromechanical systems. In SiGeP 2 , GeSnP 2 , and SnPbP 2 monolayers, hole doping is found to be an effective approach in inducing or tuning different ferromagnetic states resulting from electronic instability as reflected by van Hove singularity of band structures in the 2D systems. The results suggest that Janus XYP 2 monolayers can be promising 2D materials for applications in nanoelectronic, spintronic, and nanoelectromechanical devices.