Abstract
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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