Chemical Engineering of Altermagnetism in Two-Dimensional Metal-Organic Frameworks

Altermagnetism represents a novel magnetic phase exhibiting nonrelativistic spin splitting without net magnetization driven by lattice symmetry. Here, we introduce a general coordination-chemistry-based strategy to realize and control altermagnetic (AM) spin splitting in two-dimensional (2D) planar tetracoordinated Cr-based metal-organic frameworks (MOFs). Using density functional theory (DFT) calculations, we demonstrate that ligand symmetry and its arrangement within the lattice can be used to lower the crystallographic symmetry of Cr-based MOFs, enabling g-wave AM spin splitting up to 65 meV. Furthermore, frontier molecular orbital engineering (FMOE) allows selective ligand spin polarization, inducing a shift to d-wave AM anisotropy in polycyclic ligand-based 2D MOFs with spin splitting up to 83.9 meV. Microscopic magnetic exchange interaction (J) analysis reveals that ligand-mediated interactions dominate over metal-metal coupling, stabilizing AM order in systems with spin-polarized ligands. Interestingly, we further confirm AM spin splitting in the spin wave spectrum, where chiral magnon splitting is observed. Finally, we show that AM spin splitting gives rise to experimentally accessible charge-to-spin conversion, emerging as a linear response in d-wave and as a symmetry-allowed nonlinear effect in g-wave 2D AM MOFs. This work establishes coordination chemistry as a powerful and versatile route to symmetry control in 2D MOFs, enabling the rational design of 2D molecular materials with tunable electronic and AM properties for next-generation spintronic devices.