Twist-tuned exchange and hysteresis in a bilayer van der Waals magnet.

Moiré superlattices in twisted bilayers enable strong reconstruction of electronic band structures, giving rise to correlated phases with high tunability. Extending this concept to van der Waals magnets, we show that twisting induces spatially varying interlayer exchange interactions that can stabilize complex magnetic responses. Here, we demonstrate robust magnetic hysteresis in bilayer CrSBr upon a twist of  ~ 3°, observed as a hysteretic evolution of exciton energies that directly track the underlying magnetic configuration in field-dependent photoluminescence measurements. An analytic two-sublattice model captures this behaviour, attributing it to a twist-induced reduction of interlayer exchange that stabilizes both parallel and antiparallel spin states over a broad field range. Spatially resolved measurements reveal local variations in hysteresis loops, consistent with position-dependent modulation of magnetic parameters. In certain regions, coherent averaging over the moiré unit cell yields an effective monodomain-like response. Our results establish twist engineering as a route to programmable magnetism in two-dimensional antiferromagnets.