Defect-induced ferromagnetism in fullerenes

TL;DR

This paper uses ab initio calculations to propose that vacancy-induced ferromagnetism in rhombohedral C60 fullerene is intrinsic, explaining experimental controversies and highlighting the role of magnetic vacancies and their interactions.

Contribution

It introduces a theoretical model showing intrinsic vacancy-induced ferromagnetism in rhombohedral C60, contrasting with cubic fullerene, and explains the fragility of ferromagnetism.

Findings

Vacancies form more easily in rhombohedral C60 than in cubic phase.

Strong ferromagnetic exchange interactions exist between vacancy-containing cages.

Fusion of magnetic vacancies into nonmagnetic bivacancies explains ferromagnetism fragility.

Abstract

Based on the ab initio electronic structure calculations the picture of ferromagnetism in polimerized C60 is proposed which seems to explain the whole set of controversial experimental data. We have demonstrated that, in contrast with cubic fullerene, in rhombohedral C60 the segregation of iron atoms is energetically unprofitable which is a strong argument in favor of intrinsic character of carbon ferromagnetism which can be caused by vacancies with unpaired magnetic electrons. It is shown that: (i) energy formation of the vacancies in the rhombohedral phase of C60 is essentially smaller than in the cubic phase, (ii) there is a strong ferromagnetic exchange interactions between carbon cages containing the vacancies, and (iii) the fusion of the magnetic vacancies into nonmagnetic bivacancy is energetically profitable. The latter can explain a fragility of the ferromagnetism.