We calculate the angular dependence of the x-ray linear and circular dichroism at the L2,3 edges of α-Fe(II) Phthalocyanine (FePc) thin films using a ligand field model with full configuration interaction. We find the best agreement with the experimental spectra for a mixed ground state of 3Eg(a1g2eg3b2g1) and 3B2g(a1g1eg4b2g1) with the two configurations coupled by the spin-orbit interaction. The 3Eg(b) and 3B2g states have an easy axis and plane anisotropies, respectively. Our model accounts for an easy-plane magnetic anisotropy and the measured magnitudes of the in-plane orbital and spin moments. The proximity in energy of the two configurations allows a switching of the magnetic anisotropy from easy plane to easy axis with a small change in the crystal field, as recently observed for FePc adsorbed on an oxidized Cu surface. We also discuss the possibility of a quintet ground state (5A1g is 250~meV above the ground state) with planar anisotropy by manipulation of the Fe-C bond length by depositing the complex on a substrate that is subjected to a mechanical strain.
@article{arxiv.1405.4313,
title = {Mixed configuration ground state in Iron(II) Phthalocyanine},
author = {Javier Fernandez-Rodriguez and Brian Toby and Michel van Veenendaal},
journal= {arXiv preprint arXiv:1405.4313},
year = {2015}
}