Ferromagnetic correlation in hydrogen doped highly oriented pyrolytic graphite

The significant diamagnetism of pyrolytic graphite (PyG) allows it to be passively levitated above permanent magnet arrays and translated in the plane of these arrays via optical irradiation, which promotes applications in frictionless milli-scale robotics. Previous explanations for the translation effect have cited photothermal heating of levitated PyG and the thermal dependence of PyG’s magnetic susceptibility, as observed through measurements of samples at uniform temperatures. In this article, we offer a revision to the theory of photothermal actuation of levitated PyG. Through experiments and simulations, we demonstrate that the gradient of PyG’s diamagnetism with temperature—as measured for samples at uniform temperatures—is insufficient to explain the magnitude of forces required by the optically induced translation phenomenon. We hypothesize that the contrast in diamagnetism of PyG samples under asymmetric photothermal heating is at least an order of magnitude greater than that expected from measurements where the sample temperature is uniformly varied. We propose that the origin of the enhanced diamagnetic contrast under asymmetric optical irradiation is a photothermoelectric effect, which impacts the concentration of electrons in diamagnetically significant orbital states in graphite. To support this hypothesis, we take qualitative measurements, demonstrating the n-type thermoelectricity of PyG samples under optical irradiation while also characterizing the graphitic material with scanning electron microscopy/energy dispersive x-ray spectroscopy. We highlight the new understanding of the origin of the photothermal actuation through experiments using PyG samples with modified geometries that exhibit a pronounced preference in the axis of translation.

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Magnetic moment manipulation in hydrogen-peroxide-doped grafoil, pyrolytic graphite and Fe₃C-filled multiwall carbon nanotubes

Fayazi

Gao

et al. 2020

Nano Ex.

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Observation of granular superconductivity and percolative ferromagnetism in hydrogen/oxygen doped graphite materials has motivated recent research because of the unexplored scenarios in the field of magnetic-devices and spintronics. Here we report a novel investigation of the effects of hydrogen-peroxide-doping on the magnetic properties of grafoil, highly oriented pyrolytic graphite (HOPG) and carbon nanotube (CNT) samples characterized by specific defective characteristics. ZFC and FC magnetic curves acquired on the undoped boundary-defect-rich grafoil samples from 2 K to 300 K, revealed a spin-glass-like behaviour, with magnetic irreversibilities indicating the existence of percolative ferromagnetism. An enhancement in such effect was found in the post-doped samples below ∼70 K, together with a magnetic transition. This was evidenced further by ESR, with the appearance of a broad differential absorption peak at 77 K for g ∼ 3.54, compatible with antiferromagnetic ordering in presence of ferromagnetic multilayers. An analogous enhancement of ferromagnetic signals was found on sp3-defect-rich HOPG, with the appearance of localized ESR differential absorption features at g factors of ∼ 2.14, ∼2.08, ∼2.02, ∼ 1.91 and ∼ 1.86 at 77 K. Instead, comparisons performed in vacancy-rich doped CNTs revealed a significantly different trend, with an anomalous demagnetization of both the vacancy-rich graphitic CNT layers and encapsulated Fe3C nanowires. These observations seem to highlight a possible role of specific defects towards modifications of magnetic correlation in presence of hydrogen/oxygen species.

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Ferromagnetic correlation in hydrogen doped highly oriented pyrolytic graphite

Cited by 3 publications

References 33 publications

Evidence of ferromagnetic behaviour in carbon nanospheres synthesised by the chemical vapour deposition technique

Evidence of ferromagnetic behaviour in carbon nanospheres synthesised by the chemical vapour deposition technique

Photothermal actuation of levitated pyrolytic graphite revised

Magnetic moment manipulation in hydrogen-peroxide-doped grafoil, pyrolytic graphite and Fe₃C-filled multiwall carbon nanotubes

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Ferromagnetic correlation in hydrogen doped highly oriented pyrolytic graphite

Cited by 3 publications

References 33 publications

Evidence of ferromagnetic behaviour in carbon nanospheres synthesised by the chemical vapour deposition technique

Evidence of ferromagnetic behaviour in carbon nanospheres synthesised by the chemical vapour deposition technique

Photothermal actuation of levitated pyrolytic graphite revised

Magnetic moment manipulation in hydrogen-peroxide-doped grafoil, pyrolytic graphite and Fe3C-filled multiwall carbon nanotubes

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Product

Resources

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Magnetic moment manipulation in hydrogen-peroxide-doped grafoil, pyrolytic graphite and Fe₃C-filled multiwall carbon nanotubes