Unusual Magnetic Properties and Superconductivity in Sulfur-Doped Amorphous Carbon Powder

An amorphous carbon (a-C) powder obtained by decomposition of sucrose was mixed with sulfur and synthesized at 400 ∘C. Magnetic measurements reveal that the products obtained are inhomogeneous. Some parts show traces of superconductivity at T C=17 and 42 K. Other parts show unusual magnetic features. (i) Pronounced irreversible peaks around 50 K appear in the first zero-field-cooled (ZFC) sweep only. (ii) Unexpectedly, these peaks are totally suppressed in the second ZFC runs performed a few minutes later. Around the peak position, the field-cooled (FC) curves cross the ZFC plots, such that ZFC>FC. The two peculiar magnetic observations are connected to each other and are also ascribed to the a-C powder taken from commercial sources. The possibility that impurities cause these magnetic phenomena is excluded.