  A lot of efforts have been devoted to understanding the origin and effects of
magnetic moments induced in graphene with carbon atom vacancy, or light adatoms
like hydrogen or fluorine. At the meantime, the large negative
magnetoresistance (MR) widely observed in these systems is not well understood,
nor had it been associated with the presence of magnetic moments. In this
paper, we study the systematic evolution of the large negative MR of in-situ
hydrogenated graphene in ultra-high vacuum (UHV) environment. We find for most
combination of electron density ($n_e$) and hydrogen density ($n_H$), MR at
different temperature can be scaled to $\alpha=(\mu_BB)/[k_B(T-T^*)]$, where
$T^*$ is the Curie-Weiss temperature. The sign of $T^*$ indicates the existence
of tunable ferromagnetic-like ($T^* >0$) and anti-ferromagnetic-like ($T^* <0$)
coupling in hydrogenated graphene. However, the lack of hysteresis of MR or
anomalous Hall effect below $|T^*|$ points to the fact that long-range magnetic
order did not emerge, which we attribute to the competition of different
magnetic orders and disordered arrangement of magnetic moments on graphene. We
also find that localized impurity states introduced by H adatoms could modify
the capacitance of hydrogenated graphene. This work provides a new way to
extract information from large negative MR behavior and can be a key to help
understanding interactions of magnetic moments in graphene.
