External-field-induced altermagnetism in experimentally synthesized monolayer CrX3 (X=Cl, Br, and I)

Altermagnetism, which has recently attracted much attention in condensed matter physics, showcases captivating physical properties and holds great promise for applications in spintronics. Bulk altermagnets have been experimentally identified, while two-dimensional (2D) altermagnets remain experimentally unexplored. Here, we take experimentally synthesized 2D ferromagnetic CrX3 (X=Cl, Br, and I) as the parent material and achieve altermagnetism through an external field. First, we achieve the transition from ferromagnetism to antiferromagnetism through biaxial strain. Subsequently, we break the space inversion symmetry while preserving the mirror symmetry via an electric field or Janus engineering, thereby inducing altermagnetism with the symmetry of i-wave spin-splitting. The computational results suggest that CrCl3 can be readily tuned to exhibit altermagnetism through an external field in an experiment, thanks to its low strain threshold for magnetic phase transition. Our work provides experimentally viable materials and methods for realizing altermagnetism, which can advance the development of 2D altermagnetism.