Electron Spectroscopy and Density-Functional Study of "Ferric Wheel" Molecules

TL;DR

This study combines spectroscopic experiments and density-functional theory calculations to analyze the electronic and magnetic properties of ferric wheel molecules, revealing local moments, magnetic polarization, and exchange interactions.

Contribution

It provides a comprehensive first-principles analysis of ferric wheel molecules, integrating experimental spectroscopy with theoretical modeling to elucidate their electronic structure and magnetic interactions.

Findings

Fe local moments are 4 mu_B regardless of orientation

Oxygen atoms show magnetic polarization affecting spin states

Exchange parameter J is approximately -80 K

Abstract

The Li-centered "ferric wheel" molecules with six oxo-bridged iron atoms form molecular crystals. We probed their electronic structure by X-ray photoelectron (XPS) and soft X-ray emission spectroscopy (XES), having calculated in parallel the electronic structure of a single "ferric wheel" molecule from first-principles by tools of the density-functional theory, using, specifically, the Siesta method. The Fe local moments were found to be 4 mu_B, irrespective of their mutual orientation. Neighbouring atoms, primarily oxygen, exhibit a noticeable magnetic polarization, yielding effective spin S=5/2 per iron atom, that can get inverted as a "rigid" one in magnetic transitions. Corresponding energy preferences can be mapped onto the Heisenberg model with effective exchange parameter J of about -80 K.