Hund's rule Magnetism in C60 ions?

TL;DR

This study explores the magnetic properties of C60 ions, revealing that negative ions favor low spin states while positive ions exhibit high spin states due to competing interactions, with implications for fullerene-based magnetic materials.

Contribution

It provides a comprehensive analysis of Hund's rule magnetism in C60 ions by including both electron-vibration and electron-electron interactions with ab-initio parameters.

Findings

Negative C60 ions favor low-spin states.

Positive C60 ions favor high-spin states.

Hund's rule magnetism may occur in fullerene cation compounds.

Abstract

We investigate the occurrence of Hund's rule magnetism in C60(n+-) molecular ions, by computing the ground-state spin for all charge states n from -3 to +5. The two competing interactions, electron-vibration (e-v, including Jahn Teller, favoring low spin) and electron-electron (e-e, including Hund-rule exchange, favoring high spin), are accounted for based on previously computed ab-initio coupling parameters. Treating the ion coordinates as classical, we first calculate and classify the static Jahn-Teller distorted states for all n, inclusive of both e-v and e-e effects. We then correct the adiabatic result by including the zero-point energy lowering associated with softening of vibrations at the adiabatic Jahn-Teller minima. Our overall result is that while, like in previous investigations, low-spin states prevail in negative ions, Hund's rule high spin dominates all positive C60(n+) ions. This suggests also that Hund-rule magnetism could arise in fullerene cation-based solid state compounds, particularly those involving C60(2+).