  The electron-electron interaction in carbon nanostructures was studied. A new
method which allows to determine the electron-electron interaction constant
$\lambda_c$ from the analysis of quantum correction to the magnetic
susceptibility and the magnetoresistance was developed. Three types of carbon
materials: arc-produced multiwalled carbon nanotubes (arc-MWNTs), CVD-produced
catalytic multiwalled carbon nanotubes (c-MWNTs) and pyrolytic carbon were used
for investigation. We found that $\lambda_c$=0.2 for arc-MWNTs (before and
after bromination treatment); $\lambda_c$ = 0.1 for pyrolytic graphite;
$\lambda_c >$ 0 for c-MWNTs. We conclude that the curvature of graphene layers
in carbon nanostructures leads to the increase of the electron-electron
interaction constant $\lambda_c$.
