Reversible On/Off Switching of Altermagnetism in Two-dimensional Metal-Organic-Frameworks via Molecular Tautomerism

Abstract

Altermagnets exhibit compensated magnetic moments in real space while retaining nonrelativistic spin splitting in momentum space, offering a platform for field-robust, ultrafast spin dynamics. Yet practical routes to reversibly manipulate altermagnetic states remain limited and are dominated by structural or external-field modulation. Here, we introduce a chemical molecular-switch strategy that leverages tautomerism in organic linkers to reversibly control spin states in two-dimensional metal-organic framework (2D MOF). Using a Ni-based 2D frameworks as a representative system, we demonstrate a reversible transition between a nonmagnetic phase (Ni-L1) and an altermagnetic phase (Ni-L2) driven by solvent-assisted lactim-lactam proton transfer, with computed barriers of 0.30 eV (forward) and 0.43 eV (reverse). The altermagnetic state exhibits ligand-centered moments of ~ 0.50 µB and a characteristic spin-split electronic structure with band splitting extending across nearly the entire Brillouin zone. Symmetry analysis attributes this unusually persistent splitting to the reduced local (molecular) symmetry of the lactam linker, which removes mirror-related spin-degeneracy constraints present in higher-symmetry analogues. These results establish tautomerization as a chemically reversible handle for altermagnetic phase control in reticular materials and highlight molecular-scale symmetry as a decisive design parameter for reconfigurable altermagnetic electronics.