Switchable Altermagnetism in a Layered van der Waals Metal-Organic Framework Driven by Spin-Crossover

Dynamical control of altermagnetism is a key requirement for translating its unique spin-dependent functionalities into practical spintronic devices, yet effective switching mechanisms remain largely unexplored. Here, we open an unprecedented, versatile, and programmable route based on spin-crossover to switch altermagnetism on demand in molecular materials. Using density functional theory calculations, we demonstrate an altermagnetic ground state in the layered van der Waals metal-organic frameworks MnX2(tdz)2 (X = Cl, Br; tdz = thiadiazole), stabilized by anisotropic interlayer exchange interactions, which gives rise to a characteristic d-wave momentum-space spin splitting and an associated spin-splitter transport response. Our findings reveal that under hydrostatic pressure, a high-spin-to-low-spin transition reconfigures the Mn d-orbital occupation, thus modifying the magnetic exchange network and stabilizing a different antiferromagnetic ground state whose symmetry suppresses the nonrelativistic spin splitting. Crucially, spin-crossover switches altermagnetism not by directly altering the electronic structure but by changing the symmetry of the magnetic ground state. These results establish molecular spin-crossover altermagnets as a platform for externally reconfigurable spintronic devices.