Spin Excitations of High Spin Iron(II) in Metal–Organic Chains on Metal and Superconductor

Abstract Many‐body interactions in metal–organic frameworks (MOFs) are fundamental for emergent quantum physics. Unlike their solution counterpart, magnetization at surfaces in low‐dimensional analogues is strongly influenced by magnetic anisotropy (MA) induced by the substrate and still not well understood. Here, on‐surface coordination chemistry is used to synthesize on Ag(111) and superconducting Pb(111) an iron‐based spin chain by using pyrene‐4,5,9,10‐tetraone (PTO) precursors as ligands. Using low‐temperature scanning probe microscopy, their structures and low‐energy spin excitations of coordinated Fe atoms are compared with high S = 2 spin‐state. Although the chain and coordination centers are identical on both substrates, the long‐range spin–spin coupling due to a superexchange through the ligand on Ag is not experimentally observed on Pb(111). This reduction of spin‐spin interactions on Pb in tunneling spectra is ascribed to the depletion of electronic states around the Fermi level of the Pb(111) superconductor as compared to silver.