Abstract
We investigate the ground state and low-energy spin-orbital excitations of a single iron(II) phthalocyanine molecule in isolation and on an oxidized Cu(110) surface. Considering the subspace spanned by the three lowest spin-triplet states of and symmetry, we diagonalize the Hamiltonian made of the anisotropic spin-orbit interaction and the ligand field splitting , defined as the energy difference between and . We find that the ground state switches from a -like state with large orbital moment and out-of-plane easy axis for meV to a -like singlet state with in-plane easy axis for meV. The analysis of the first excited states in the two regimes explains the zero-field splitting data reported for -FePc as well as for FePc molecules adsorbed on an oxidized Cu(110) surface [N. Tsukahara et al., Phys. Rev. Lett. 102, 167203 (2009)]. Importantly, the calculated magnetic susceptibility obtained with the ab initio value meV compares remarkably well with the experimental data of -FePc in the whole available temperature range of 1–300 K.
- Received 15 July 2018
- Revised 13 September 2018
DOI:https://doi.org/10.1103/PhysRevB.98.195108
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