Electric-Field-Switchable Altermagnetism via Ligand Rotation in a d0 Metal-Organic Framework

Abstract

Altermagnetism combines vanishing net magnetization with momentum-dependent spin splitting. While altermagnetic signatures have been identified in metal-organic frameworks (MOFs), non-invasive reversible control remains challenging. Here we report a route to electric-field-switchable altermagnetism in a flexible d0-MOF, in which polar substituents couple the external field to ligand rotation. In the planar ground state, pz orbitals mediate 180-degree ligand-metal-ligand superexchange (J2), stabilizing antiferromagnetic order. Rotating ligands out of plane activates px/py orbitals, enhances 90-degree pathways (J1), and reverses J1/J2 competition. The antiferromagnetic-to-altermagnetic crossover occurs at approx. 34 degrees, with spin splitting of 84 meV at 90 degrees. The 90-degree altermagnetic state is switched on by the electric field and switched off upon field removal, as the constrained-rotation landscape decreases monotonically back toward 0 degrees, enabling barrierless relaxation to the antiferromagnetic state and reversible on/off operation. Ab initio molecular dynamics at 300 K shows thermal fluctuations alone cannot synchronize ligand rotation. Polar substituents provide the required coupling for electric-field control; for fluorinated substituents, the critical field is approx. 0.22 V/Angstrom, comparable to field-effect devices. This work establishes ligand p orbitals, rather than transition-metal d orbitals, as the origin of altermagnetic order and shows that polar substituents enable electric-field control for organic spintronics.