  The orbital diamagnetic susceptibility is calculated in monolayer and bilayer
graphenes with band gap as well as in three-dimensional Dirac systems. It is
demonstrated that the pseudo-spin degree of freedom such as valleys produces
paramagnetic susceptibility in an equal manner as the real spin dominating over
the Landau diamagnetism. The pseudo-spin paramagnetism explains the origin of a
singular diamagnetism which is present only in the band-gap region and
disappears rapidly inside the conduction and valence bands.
