Electrical control over the Fe(II) spin crossover in a single molecule: Theory and experiment

We report on theoretical and experimental work involving a particular molecular switch, an [FeII(L)₂]²⁺ complex, that utilizes a spin transition (``crossover''). The hallmark of this transition is a change of the spin of the metal ion, SFe=0 to SFe=2, at fixed oxidation state of the Fe ion. Combining density functional theory and first principles calculations, we demonstrate that within a single molecule this transition can be triggered by charging the ligands. In this process the total spin of the molecule, combining metal ion and ligands, crosses over from $S=0$ to $S=1$. Three-terminal transport through a single molecule shows indications of this transition induced by electric gating. Such an electric field control of the spin transition allows for a local, fast, and direct manipulation of molecular spins, an important prerequisite for molecular spintronics.