Enhanced percolative spin-glass-like behavior in oxygen-rich highly oriented pyrolytic graphite with anomalous non-hexagonal superlattices and doubled electron diffraction patterns

Abstract

The recent observations of superconductive-signals in grafoil and highly-oriented-pyrolytic-graphite (HOPG) have evidenced existence of unknown-defects responsible of electron-correlation-phenomena. Existence of anomalous-super-periodicities and doubled-diffraction-patterns has been also reported. Here we present an in-depth investigation of the structural-magnetic relationship of HOPG samples with unusual oxygen rich characteristics. By employing high-resolution-transmission-electron-microscopy (HRTEM) and selective-area-electron-diffraction (SAED) we demonstrate the appearance of non-hexagonal and hexagonal Moiré super-periodicities, with anomalous doubled electron diffraction patterns, in μm-thin lamellae exfoliated from HOPG. The hexagonal Moiré superlattices (D ~ 5.0 nm corresponding to θrot ~ 2.8o) highlight the presence of rotational misorientations between the graphitic layers and complex interfaces. Further, graphene oxide phases in direct interfacial contact with the graphitic layers were identified. Raman-spectroscopy evidenced D, D’ and G-bands compatible with the presence of sp3- and vacancy-rich configurations in proximity of the HOPG edges. Superconducting-quantum-interference-device (SQUID) revealed an enhanced spin-glass-like ferromagnetic behaviour. This observation was further confirmed by additional magnetometry measurements performed on graphite oxide. A diamagnetic background was found in all the analysed samples, while no superconductive signals were detected.

Keywords

• HOPG
• Exfoliation
• Non hexagonal superlattice
• Hexagonal superlattice
• Ferromagnetism
• Spin-glass-like behaviour