Electronic Structure and Magnetism of [(FePc)_nH₂Pc] Superlattices: A First-principles Study

Recent experimental work on quasi-1D [(FePc)_nH₂Pc] superlattices by Vargas et al. revealed interesting magnetic properties. In this study we applied density functional theory (DFT) with the Hubbard U correction to examine two model systems, [(FePc)_nH₂Pc] with n = 3 and 4. Since FePc systems are prone to local energy minima due to different d-orbital occupations, we used d-orbital occupation matrix control and identified a lower energy state compared to previous studies. Our calculations included spin-orbit interactions that are done self-consistently. Based on DFT total energies, we estimate the exchange coupling constants and zero-field-splitting parameters for an effective spin Hamiltonian of each superlattice. We found that an FePc molecule adjacent to an H₂Pc molecule has smaller on-site magnetic anisotropy. The exchange interaction between two FePc molecules that are separated by an H₂Pc molecule is over 600 times smaller than that between two adjacent molecules. The antisymmetric exchange or the Dzyaloshinskii–Moriya interaction is two orders smaller than the isotropic exchange interaction. Finally, we present calculated magnetization and magnetic susceptibility for both [(FePc)₃H₂Pc] and [(FePc)₄H₂Pc] superlattices. We hope to shed some light on the application of MPc systems to quantum information science. Further studies of spin dynamics are underway.