Prediction of tunable room-temperature ferromagnetism, ferroelectricity, and ferroelasticity in a CrNCl monolayer

Two-dimensional (2D) multiferroic materials combining intrinsic ferroelectricity, ferromagnetism, and ferroelasticity, which promise piezomagnetoelectric effects, are highly desired for their potential applications in high-density and multi-functional spintronic devices. However, a room-temperature 2D triferroic semiconductor has never been reported. Here, on the basis of first-principle calculations, we predict that the CrNCl monolayer is a potential 2D triferroic semiconductor with ferroelectricity, ferromagnetism, and ferroelasticity coexisting and strongly coupling at room temperature. The strong d-p hybridizations between Cr and N ions give rise to Cr-N dimerizations, leading to spontaneous symmetry-breaking and an in-plane electric polarization, as well as a remarkable enhancement of ferromagnetic super-exchange interactions. Moreover, the ferroelastic transition is accompanied by a 90 degrees rotation of the in-plane electric polarization and the magnetic easy axis, suggesting a strong piezo-magnetoelectric effect. These findings provide insights into multiferroic behaviors in 2D systems and can help facilitate further advancements in spintronics.