Giant Enhancement and Anomalous Thermal Hysteresisof Saturation Moment in Magnetic Nanoparticles Embedded in MultiwalledCarbon Nanotubes.

We report high-energy synchrotronX-ray diffraction spectrum andhigh-temperature magnetic data for multiwalled carbon nanotubes (MWCNTs)embedded with Fe and Fe3O4nanoparticles. Weunambiguously show that the saturation moments of the embedded Feand Fe3O4nanoparticles are enhanced by a factorof about 3.0 compared with what would be expected if they would beunembedded. More intriguingly the enhanced moments were completelylost when the sample was heated up to 1120 K, and the lost momentswere completely recovered through two more thermal cycles below 1020K. These novel results cannot be explained by the magnetism of theFe and Fe3O4impurity phases, the magnetic proximityeffect between magnetic nanoparticles and carbon, and the ballistictransport of MWCNTs. [ABSTRACT FROM AUTHOR]