Orbital-pseudospin switching reconstructs the competing exchange network in monolayer VN

Orbital degrees of freedom provide an efficient microscopic route for controlling exchange interactions in two-dimensional magnets, but a clear structural handle for switching orbital-polarized exchange networks remains rare. Here, using first-principles calculations and Monte Carlo simulations, we identify planar rectangular monolayer VN as an itinerant ferromagnet with an out-of-plane easy axis and an equilibrium Curie temperature of about 420 K. At equilibrium, the rectangular crystal field polarizes the dxz/dyz doublet, producing a direction-resolved exchange network in which strong ferromagnetic Ja and diagonal Jab couplings coexist with an antiferromagnetic Jb channel. By tuning the lattice parameter b at fixed a, the rectangular field is continuously varied through the square geometry, driving a dxz-to-dyz orbital-pseudospin reversal. This orbital redistribution converts Jb from antiferromagnetic to ferromagnetic and reconstructs the competing exchange topology into a cooperative ferromagnetic network, raising TC to a broad plateau around 490 K, corresponding to an enhancement of about 18%. Orbital-resolved ICOHP analysis shows that the static V-N bonding and the pz-mediated π channel weaken overall under b-axis tuning, ruling out bond strengthening as the origin of the exchange enhancement. These results establish rectangular-distortion-driven orbital-pseudospin switching as a microscopic mechanism for engineering robust above-room-temperature ferromagnetism in two-dimensional metallic magnets.