  We calculate the spin transport of hydrogenated graphene using the
Landauer-B\"uttiker formalism with a spin-dependent tight-binding Hamiltonian.
The advantages of using this method is that it simultaneously gives information
on sheet resistance and localization length as well as spin relaxation length.
Furthermore, the Landauer-B\"uttiker formula can be computed very efficiently
using the recursive Green's function technique. Previous theoretical results on
spin relaxation time in hydrogenated graphene have not been in agreement with
experiments. Here, we study magnetic defects in graphene with randomly aligned
magnetic moments, where interference between spin-channels is explicitly
included. We show that the spin relaxation length and sheet resistance scale
nearly linearly with the impurity concentration. Moreover, the spin relaxation
mechanism in hydrogenated graphene is Markovian only near the charge neutrality
point or in the highly dilute impurity limit.
