Mixed configuration ground state in Iron(II) Phthalocyanine

TL;DR

This study models the magnetic anisotropy of Iron(II) Phthalocyanine, revealing a mixed ground state with tunable magnetic properties influenced by configuration interactions and external strain.

Contribution

It introduces a ligand field model with full configuration interaction to explain the mixed ground state and magnetic anisotropy in FePc, aligning with experimental spectra and suggesting controllable magnetic switching.

Findings

Mixed ground state of $^3E_{g}$ and $^3B_{2g}$ configurations.

Easy-plane magnetic anisotropy consistent with experimental data.

Potential to switch magnetic anisotropy via small crystal field changes.

Abstract

We calculate the angular dependence of the x-ray linear and circular dichroism at the $L_{2,3}$ edges of $\alpha$-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 $^3E_{g}(a_{1g}^2e_g^3b_{2g}^1)$ and $^3B_{2g}(a_{1g}^1e_g^4b_{2g}^1)$ with the two configurations coupled by the spin-orbit interaction. The $^3E_{g}(b)$ and $^3B_{2g}$ 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 ($^5A_{1g}$ 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.