Kipgen, L.; Bernien, M.; Ossinger, S.; Nickel, F.; Britton, A.J.; Arruda, L.M.; Naggert, H.; Luo, C.; Lotze, C.; Ryll, H.; Radu, F.; Schierle, E.; Weschke, E.; Tuczek, F.; Kuch, W.: Evolution of cooperativity in the spin transition of an iron(II) complex on a graphite surface. Nature Communications 9 (2018), p. 2984/1-8
10.1038/s41467-018-05399-8
Open Accesn Version

Abstract:
Cooperative effects determine the spin-state bistability of spin-crossover molecules (SCMs). Herein, the ultimate scale limit at which cooperative spin switching becomes effective is investigated in a complex [Fe(H2B(pz)2)2(bipy)] deposited on a highly oriented pyrolytic graphite surface, using x-ray absorption spectroscopy. This system exhibits a complete thermal- and light-induced spin transition at thicknesses ranging from submonolayers to multilayers. On increasing the coverage from 0.35(4) to 10(1) monolayers, the width of the temperature-induced spin transition curve narrows significantly, evidencing the buildup of cooperative effects. While the molecules at the submonolayers exhibit an apparent anticooperative behavior, the multilayers starting from a double-layer exhibit a distinctly cooperative spin switching, with a free-molecule-like behavior indicated at around a monolayer. These observations will serve as useful guidelines in designing SCM-based devices.