Magnetic properties of polymerized C$_{60}$ with Fe

TL;DR

This study shows that ferromagnetism observed in polymerized C60 with Fe is due to iron carbide Fe3C formed during high-pressure, high-temperature treatment, leading to a re-evaluation of previous claims of ferromagnetic carbon.

Contribution

It demonstrates that the ferromagnetic signals in Fe-C60 samples originate from Fe3C, not from intrinsic carbon ferromagnetism, challenging prior interpretations.

Findings

Fe3C forms during high-pressure, high-temperature treatment of Fe and C60.

The magnetic properties match those of Fe3C, not ferromagnetic carbon.

Previous claims of ferromagnetic carbon are retracted based on these results.

Abstract

We provide evidence that high-pressure high-temperature (2.5 GPa and 1040 K) treatment of mixtures of iron with fullerene powders leads to the complete transformation of iron into iron carbide Fe$_3$C. The comparison of the magnetic properties (Curie temperature and magnetic moment) of the here studied samples and those for the ferromagnetic polymer Rh-C$_{60}$ indicates that the main ferromagnetic signal reported in those samples is due to Fe$_3$C and not related to the ferromagnetism of carbon as originally interpreted. Taking into account the results obtained in this study the original paper on ``Magnetic carbon" (Nature {\bf 413}, 716 (2001)) was recently retracted.