Role of the Magnetic Anisotropy in Atomic-Spin Sensing of 1D Molecular Chains

Abstract

One-dimensional metal–organic chains often possess a complex magnetic structure susceptible to modification by alteration of their chemical composition. The possibility to tune their magnetic properties provides an interesting playground to explore quasi-particle interactions in low-dimensional systems. Despite the great effort invested so far, a detailed understanding of the interactions governing the electronic and magnetic properties of the low-dimensional systems is still incomplete. One of the reasons is the limited ability to characterize their magnetic properties at the atomic scale. Here, we provide a comprehensive study of the magnetic properties of metal–organic one-dimensional (1D) coordination polymers consisting of 2,5-diamino-1,4-benzoquinonediimine ligands coordinated with Co or Cr atoms synthesized under ultrahigh-vacuum conditions on a Au(111) surface. A combination of integral X-ray spectroscopy with local-probe inelastic electron tunneling spectroscopy corroborated by multiplet analysis, density functional theory, and inelastic electron tunneling simulations enables us to obtain essential information about their magnetic structures, including the spin magnitude and orientation at the magnetic atoms, as well as the magnetic anisotropy.

Electronic band structure of 1D π–d hybridized narrow-gap metal–organic polymers

“…Such non-dispersive band character along k x implies that orbitals are localized within the Co-QDI chains and there is no interchain coupling. 19,33 This is consistent with the separated chain conformation observed in STM [Fig. 1(a)].…”

“…Moreover, with LT-STM/STS we explored the LDOS which reveals several occupied peaks in the VB region and we assigned a 1.25 eV narrow bandgap to Co-QDI, signaling the semiconducting character of the MO chains. These findings are supported by GW 0 band structure calculations showing that the observed bands emanate from the efficient hybridization of Co(3d) and molecular orbitals promoting efficient electron delocalization along the polymers, in agreement with recent GGA+U calculations 19 (Fig. S9 †).…”

“…In the energy range very close to the Fermi level, recent experiments found in Cr-QDI an underscreened Kondo effect, while for Co-QDI such a behavior was not observed. 19 The latter is caused by the presence of large magnetic anisotropy and high-spin state (S = 3/2) of the Co-QDI chains.…”

“…18 A comprehensive study of the magnetic properties of Co-QDI and Cr-QDI MO polymers was recently provided, whereby Co atoms in Co-QDI are found in a high spin S ∼ 3/2 ground state with a strong easy axis of magnetization along the in-plane direction while Cr in Cr-QDI has spin S = 2 and an easy-axis of magnetization perpendicular to the surface. 19 However, an experimental determination of their predicted weakly dispersive and dispersive bands is still pending.…”

Synthesizing Cr‐Based Two‐Dimensional Conjugated Metal‐Organic Framework Through On‐Surface Substitution Reaction

“…The high binding energy, however, hinders the reversible breaking of the bis(diimino)‐Cr coordination bonds, and hampers the error correction and crystallization of the Cr 3 (HITP) 2 framework during annealing. [ 16 ] Thus, through on‐surface coordination assembly, one can get high‐quality 1D Cr‐QDI chains and Ni 3 (HITP) 2 frameworks, [ 12a,d,15 ] but only got irregular branches when involving Cr atoms and HITP ligands (Figure 1b). Interestingly, the higher binding energy for Cr makes it energetically favorable to substitute Cr for Ni in the Ni 3 (HITP) 2 framework.…”