Atomic Scale Evidence of the Switching Mechanism in a Photomagnetic CoFe Dinuclear Prussian Blue Analogue

Molecular complexes based on Prussian Blue analogues have recently attracted considerable interest for their unique bistable properties combined to ultimately reduced dimensions. Here, we investigate the first dinuclear FeCo complex exhibiting both thermal and photomagnetic bistability in the solid state. Through an experimental and theoretical approach combining local techniques-X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and ligand field multiplet calculations-we were able to evidence the changes occurring at the atomic scale in the electronic and magnetic properties. The spectroscopic studies were able to fully support at the atomic level the following conclusions: (i) the 300 K phase and the light-induced excited state at 4 K are both built from Fe-LS(III)-Co-HS(II) paramagnetic pairs with no apparent reorganization of the local structure, (ii) the 100 K phase is composed of Fe-LS(II)-Co-LS(III) diamagnetic pairs, and (iii) the light-induced excited state is fully relaxed at an average temperature of approximate to 50 K. In the paramagnetic phase at 2 K, XAS and XMCD reveal that both Fe and Co ions exhibit a rather large orbital magnetic moment (0.65 mu(B) and 0.46 mu(B), respectively, under an external magnetic induction of 6.5 T), but it was not possible to detect a magnetic interaction between spin centers above 2 K.