Multiferroicity in two dimensional Co₂Cl₂ monolayer

Multiferroicity has been studied for about 70 years and resurging recently due to rapid experimental and theoretical advances. However, two-dimensional ferromagnetic-ferroelastic multiferroicity, which is crucial to magneto-elastic nanodevices, is still very rare. Here, we propose that the Co₂Cl₂ monolayer exhibits ferromagnetic-ferroelastic multiferroicity. The system has two asymmetric phases: FE-I, a metallic ferromagnetic phase, and FE-II, a semiconducting antiferromagnetic phase, which can be switched by strain. We show that Co₂Cl₂ monolayers undergo both metal-insulator and ferromagnetism-antiferromagnetism transitions due to the different crystal fields surrounding Co²⁺ ions. Interestingly, both the ferromagnetic and antiferromagnetic phases exhibit high critical temperatures, making this material promising for device applications.