Charge transfer governed interlayer magnetic coupling and symmetry breaking in a van der Waals magnet.

Van der Waals (vdW) magnets provide a rich landscape for innovative spintronic applications at atomic thickness. Among them, chromium sulfide bromide (CrSBr) stands out as a semiconducting antiferromagnet with the potential for magnetoelectric manipulation. However, the detection and electrical control of 2D magnetism in CrSBr are constrained by its centrosymmetric structure and in-plane antiferromagnetism. To address this challenge, we construct heterostructure devices composed of trilayer CrSBr and monolayer graphene, where interfacial charge transfer breaks the inversion symmetry of both magnetic order and crystallographic structure. The inversion symmetry breaking by charge transfer thus allows a full discrimination of the otherwise degenerate magnetic states using optical second harmonic generation, including the charge transfer induced intermediate magnetic states that consist of antiferromagnetic and ferromagnetic vdW interfaces. Furthermore, gate voltage enables the tuning of charge transfer, effectively modulating the interlayer magnetic coupling and magnetic transitions. Our findings deepen the understanding of optospintronic interaction and magnetoelectric manipulation in vdW magnets, paving the way for electrically tunable 2D spintronic devices.