Spin reorientation and controllable magnetic anisotropy in two-dimensional MnSe2/As van der Waals heterostructures.

First-principles calculations demonstrate that interfacial coupling in MnSe2/As van der Waals heterostructures induces spin reorientation, switching the easy-magnetization axis of the MnSe2 monolayer from in-plane to out-of-plane. Interlayer charge transfer generates a built-in electric field directed from the As layer toward MnSe2, which drives this spin reorientation. The magnetocrystalline anisotropy energy (MAE) is found to be broadly tunable via external electric fields, interlayer distance variation, and thickness of the As layer. Crucially, perpendicular magnetic anisotropy (PMA) enhancement is achieved via applied electric fields and reduced interlayer spacing. Atomic-resolved MAE and orbital-resolved MAE analysis combined with density of states calculations reveal that the PMA enhancement primarily originates from modified electronic states of Se-p orbitals. This work establishes a viable strategy for tailoring 2D magnetic properties and may be helpful for preparing 2D spintronic devices.