Giant Moment Enhancement of Magnetic Nanoparticles Embedded in Multi-Walled Carbon Nanotubes: Consistent with Ultrahigh Temperature Superconductivity

Abstract

There are reports of intrinsic weak ferromagnetism in graphite and carbon-based materials well above room temperature Cervenka et al. (2009); Esquinazi et al. (2003); Kopelevich et al. (2000); Mendoza et al. (1999); Moehlecke et al. (2002); Mombru et al. (2005), as well as a theoretical prediction of a ferromagnetic instability in graphene sheets Bas & Jafari (2002). On the other hand, Dzwilewski et al. Talyzin et al. (2007) show that the observed high-temperature ferromagnetism in rhombohedral C60 Makarova et al. (2001) is not intrinsic but caused by contamination of magnetic impurities. In addition to the observation of unusual high-temperature ferromagnetism in the carbon-based materials, there was a report of extra magnetic moment induced in graphite due to a large magnetic proximity effect between graphite and magnetic nanoparticles Coey et al. (2002). Similarly, high-temperature magnetic data of multi-walled carbon nanotube (MWCNT) mat samples embedded with Fe and Fe3O4 nanoparticles Zhao et al. (2008) indicated that the room-temperature saturation magnetizations of the magnetic nanoparticles embedded in the MWCNTs are enhanced by a factor of about 3 as compared with what they would be expected to have for free magnetic nanoparticles. Recently, the study has been extended to nickel nanoparticles embedded in MWCNTs Wang et al. (2010) and shown a similar enhancement factor. More intriguringly, there were reports of ultrahigh temperature superconducting behaviors in carbon films Antonowicz (1974); Lebedev (2004), carbon nanotubes Zhao & Wang (2001); Zhao (2004; 2006), graphite Kopelevich et al. (2000), and graphite-sulfur composites Da Silva et al. (2001); Moehlecke et al (2004). Highly oriented pyrolithic graphite (HOPG) was shown to display either a partial superconducting or a ferromagnetic-like response to an applied magnetic field up to 400 K Kopelevich et al. (2000). The existence of ultrahigh temperature superconductivity in the carbon-based materials is not accidental. The unique electronic structures of the carbon-based materials make them 16