Abstract:

The electronic properties of boron-doped multiwall carbon nanotubes (MWNTs) have been studied using static magnetization and electron spin resonance. A relatively strong ferromagnetic signal has been identified in the dc magnetization response that shows the occurrence of ferromagnetism, coexisting with the orbital and spin magnetism of the conduction electrons. The small diamagnetic susceptibility and the weak temperature variation of the g factor, which is observed in the narrow conduction-electron spin resonance (CESR), indicate a Fermi level shift of ∼0.2eV, according to the quasi-two-dimensional graphite band model. The temperature dependence of the spin susceptibility reveals considerable enhancement compared to undoped MWNTs and the presence of thermally activated behavior, complying with an increased density of states and the formation of localized impurity states close to the Fermi level. Line-shape analysis of the CESR spectra in terms of two separate spin systems implies enhanced doping inhomogeneity. © 2005 The American Physical Society.

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