Nonlinear field-dependent susceptibilities of C 60 and carbon nanotubes

Abstract

We have found strongly nonlinear, field-dependent magnetic susceptibilities in a range of carbon-based materials such as C60, carbon nanotubes, diamond and graphite. This nonlinear behaviour is prominent at low fields and it vanishes at relatively high fields. We have interpreted this phenomenon in terms of the field dependence of the spectral energy separations of the van Vleck paramagnetic term of the susceptibility. Our results should have significant bearing on the interpretation of the magnetic properties of this class of materials.