Temperature-, Light-, and Soft X-ray-Induced Spin Crossover in a Single Layer of FeII-Pyrazolylborate Molecules in Direct Contact with Gold

Understanding the properties of spin-crossover molecules in direct contact with metals is crucial for their future integration in electronic and spintronic devices. By X-ray absorption spectroscopy, we investigate the properties of FeII((3,5-(CH3)2Pz)3BH)2 molecules in the form of monolayer islands on a metallic substrate, namely, Au(111). We demonstrate that the spin-crossover transition can be thermally induced from the high spin state to a mixed spin state phase containing one-third of high-spin-state and two-thirds of low-spin-state molecules in agreement with previous work by scanning tunneling microscopy. In addition, at 4.4 K, the spin crossover from the low spin state to the high spin state can also be induced by X-ray and by light excitations.