  Recently, there have appeared theoretical works on the magnetic properties of
graphene and graphene nanoribbons envisaging possible spin-based applications
along with fundamental scientific insight. The theoretical efforts, however,
appear not paralleled by experimental investigation to test magnetic
properties. Yet, room temperature ferromagnetism (RTFM) has recently been
experimentally reported in graphene (G-600) [Nano. Letters 9, 220 (2009)], the
origin of which remains still unexplored. Inspired by this observation, and in
attempt to trace the origin of RTFM, we here report on low temperature K-band
electron spin resonance (ESR) observations on G-600. Two distinct C-related
paramagnetic signals are revealed, both of a Lorentzian shape: a) a broad at g
= 2.00278 which can be attributed to graphitic-like (GL) carbon; b) a narrower
signal at g = 2.00288 which is associated with free radical like (FL) carbon.
No other signals could be detected. We speculate that the GL ESR signal may
come from the conductive {\pi}-carriers propagating in the interior of graphene
sheets, while the FL ESR signal may stem from the edges of graphene sheets due
to non-bonding localized electronic states. It is suggested that the long range
direct/indirect exchange interaction between GL and FL C-related magnetic spin
centers may lead to the reported RTFM, this pointing to C origin of the later.
