Direct ESR evidence for magnetic behaviour of graphene

TL;DR

This study provides experimental ESR evidence of magnetic behavior in graphene, identifying specific paramagnetic signals that suggest a C-based origin for room temperature ferromagnetism, bridging theoretical predictions with experimental data.

Contribution

First experimental ESR investigation of magnetic properties in graphene revealing specific C-related paramagnetic signals linked to ferromagnetism.

Findings

Identification of two distinct C-related ESR signals in graphene.

Association of signals with graphitic-like and free radical-like carbon.

Implication of exchange interactions between these centers for ferromagnetism.

Abstract

Recently, there have appeared theoretical works on the magnetic properties of graphene and graphene nanoribbons envisaging possible spin-based applications along with fundamental scientific insight. The theoretical efforts, however, appear not paralleled by experimental investigation to test magnetic properties. Yet, room temperature ferromagnetism (RTFM) has recently been experimentally reported in graphene (G-600) [Nano. Letters 9, 220 (2009)], the origin of which remains still unexplored. Inspired by this observation, and in attempt to trace the origin of RTFM, we here report on low temperature K-band electron spin resonance (ESR) observations on G-600. Two distinct C-related paramagnetic signals are revealed, both of a Lorentzian shape: a) a broad at g = 2.00278 which can be attributed to graphitic-like (GL) carbon; b) a narrower signal at g = 2.00288 which is associated with free radical like (FL) carbon. No other signals could be detected. We speculate that the GL ESR signal may come from the conductive {\pi}-carriers propagating in the interior of graphene sheets, while the FL ESR signal may stem from the edges of graphene sheets due to non-bonding localized electronic states. It is suggested that the long range direct/indirect exchange interaction between GL and FL C-related magnetic spin centers may lead to the reported RTFM, this pointing to C origin of the later.