Model Hamiltonian approach to the magnetic anisotropy of iron phthalocyanine at solid surfaces

Abstract

We present a model Hamiltonian approach to evaluate the effect of adsorption on magnetic anisotropy of an iron-phthalocyanine (FePc) molecule. We describe the electronic ground state as a mixed configuration consisting of the $^{3}E$ and $^{3}B_{2}$ states under the ${C}_{4v}$ symmetry, which well reproduces the magnetic properties measured for the bulk FePc. We focus on the deformation of each $3d$ orbital and the modification of the ligand-field splitting by hybridization with the substrate electronic states. As an interesting example, we evaluate the $d$-orbital deformation in FePc on Au(111) from the density functional theory calculations, and demonstrate that the respective $d$-orbital deformation and the modification of the ligand-field splitting affect magnetic anisotropy through change of the mixed nature in the ground state. In addition, we propose that inelastic electron tunneling spectroscopy with a cryogenic scanning tunneling microscope is a promising tool to verify the mixed configuration by measuring the low-energy excited states and evolutions to external magnetic fields.