  The energy and persistent current spectra for a relativistic fermion on a
ring is studied in details. The nonlinear nature of persistent current in
relativistic regime and its dependence on particle mass and ring radius are
analysed thoroughly. For a particular ring radius we find the existence of a
critical mass at which the single ring current doesn't depend on the flux. In
lower mass regime the total current spectrum shows plateaus at different height
which appears periodically. The susceptibility as well shows periodic nature
with amplitude depending on particle mass. As we move from higher mass to lower
mass regime, we find that the system turns into paramagnetic from diamagnetic.
We also show that same behaviour is observed if one vary the radius of the ring
for a fixed particle mass. Hence the larger ring will be diamagnetic while the
smaller one will be paramagnetic. Finally we propose an experiment to verify
our findings.
