Recent advances in two-dimensional Janus magnetic monolayers

Two-dimensional (2D) Janus monolayers with intrinsic magnetism have drawn increasing attention due to their broken out-of-plane symmetry and unique multifunctional properties. This review systematically surveys the current theoretical progress on magnetic Janus monolayers, focusing on their fundamental physical characteristics and emerging quantum phenomena. The review begins by introducing the basic physical properties of typical magnetic Janus systems, including their crystal structures and electronic band structures, followed by a discussion of the underlying magnetic exchange interactions governed by the Heisenberg model and the competition between direct and superexchange couplings. The critical role of magnetic anisotropy energy (MAE) in stabilizing long-range magnetic order against thermal fluctuations, as well as the effects of strain engineering on modulating exchange interactions and MAE, are then examined. Subsequently, several emergent phenomena arising from the broken inversion symmetry of Janus architectures are presented, including piezoelectricity, the quantum anomalous Hall effect (QAHE), and valley polarization. This review aims to provide a structured reference for understanding the current landscape of 2D magnetic Janus monolayers and to offer guidance for designing future spintronic, valleytronic, and topological devices.