The understanding and control of the magnetic properties of carbon-based materials is of fundamental relevance in applications in nano- and biosciences. Ring currents do play a basic role in those systems. In particular the inner cavities of nanotubes offer an ideal environment to investigate the magnetism of synthetic materials at the nanoscale. Here, by means of 13C high resolution NMR of encapsulated molecules in peapod hybrid materials, we report the largest diamagnetic shifts (down to -68.3 ppm) ever observed in carbon allotropes, which is connected to the enhancement of the aromaticity of the nanotube envelope upon doping. This diamagnetic shift can be externally controlled by in situ modifications such as doping or electrostatic charging. Moreover, defects such as C-vacancies, pentagons, and chemical functionalization of the outer nanotube quench this diamagnetic effect and restore NMR signatures to slightly paramagnetic shifts compared to nonencapsulated molecules. The magnetic interactions reported here are robust phenomena independent of temperature and proportional to the applied magnetic field. The magnitude, tunability, and stability of the magnetic effects make the peapod nanomaterials potentially valuable for nanomagnetic shielding in nanoelectronics and nanobiomedical engineering.
Bibliographical noteFunding Information:
This work was supported by the Centre National de la Recherche Scientifique and the Region Languedoc-Roussillon, the Office of Basic Energy Sciences, Materials Sciences and Engineering Division, the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, via the sp2-bonded nanostructures program and the Molecular Foundry, the Wenner-Gren Foundations, and Vetenskapsrådet, the Spanish MEC (Grant No. FIS2007-65702-C02-01), Grupos Consolidados UPV/EHU of the Basque Country Government (Grant No. IT-319-07), and European Community e-I3 ETSF project. Y.K. and E.A.-H. contributed equally to this work.
ASJC Scopus subject areas
- General Physics and Astronomy
- Physical and Theoretical Chemistry