Abstract
Presence of high temperature superconductivity in highly-oriented-pyrolytic-graphite (HOPG) and water-doped-graphite has recently attracted important attention. In the latter, analogy with red-wine-doped FeTe1−x Sx superconductors has been proposed. We report a novel T-XRD investigation of red-wine-doped-HOPG at the magic angle (average θmisfit between the layers ∼0.8° as revealed by TEM and Moiré pattern analyses) from 77 K to 673 K. Anomalous T-induced depletion in the intensity of the 004 HOPG-reflection from 77 K to 348 K is demonstrated. Similar depletion features could be also found in comparative measurements performed in water doped HOPG samples. Significant deviation from the linear c-axis expansion predicted by the α-factor is shown together with a depletion in the graphitic c-axis shift-values for wine doped samples. EPR analyses are also provided and reveal a transition at 77 K implying possible presence of a change in the magnetic ordering (i.e. ferromagnetism) at low temperature. VSM analyses supported further the T-XRD results, by revealing presence of magnetic transition at approx. 350 K together with unusual superconductive-like hysteretic features at 250 K and 300 K which are not compatible with ferromagnetism.
Published Version
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