Defect-induced magnetism in graphite through neutron irradiation

TL;DR

This study demonstrates that neutron irradiation induces defect-related paramagnetism in graphite, with structural defects correlating to increased magnetic signals, but no long-range magnetic order is observed.

Contribution

It provides experimental evidence linking neutron-induced defects to magnetism in graphite and explores the role of different defect types through theoretical calculations.

Findings

Neutron irradiation increases paramagnetism in graphite.

Structural defects correlate with magnetic signal enhancement.

No magnetic order observed in bulk graphite.

Abstract

We have investigated the variation in the magnetization of highly ordered pyrolytic graphite (HOPG) after neutron irradiation, which introduces defects in the bulk sample and consequently gives rise to a large magnetic signal. We observe strong paramagnetism in HOPG, increasing with the neutron fluence. We correlate the induced paramagnetism with structural defects by comparison with density-functional theory calculations. In addition to the in-plane vacancies, the trans-planar defects also contribute to the magnetization. The lack of any magnetic order between the local moments is possibly due to the absence of hydrogen/nitrogen chemisorption, or the magnetic order cannot be established at all in the bulk form.